Download Android Widgets and Event Handling

ELET4133: Embedded Systems
Topic 9
Widget Event Handling
Originals of Slides and Source Code for Examples:
http://www.coreservlets.com/android-tutorial/
Agenda
• Develop an App to change the colors of the
main screen (a TextView)
• Will use three approaches
– Use a separate Listener class
– Use a named inner class
– Use an anonymous inner class (AIC)
• All approaches work well with multiple controls
– Use the same event handler
– But pass parameters (like the color) into it
9/27/2013
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2
The App
• The App will appear as shown in the emulator
Buttons
Vertical
Linear
Layout
Buttons3 Radio
Button Group
Text Area
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3
The App
• The App will
– Change the color of the TextView area when a Button or
a RadioButton is pressed.
– Different colors depending on which pressed.
• Approach
– Use an external class that implements
View.OnClickListener
– Import android.view.View.OnClickListener
• use “implements OnClickListener”
• A “Listener” is a class that waits for an event to occur
– When the event occurs it causes this class to execute
9/27/2013
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4
The Advantages/Disadvantages
• The advantages and disadvantages to this
approach
– Advantages
• You can pass arguments to change behavior
• Separate classes generally promote loose coupling
– So, if event handler can be applied to different controls, it
can be change independently from rest of app.
– Disadvantages
• If you want to call the code in main Activity, you
need a reference
– Even then, that code in the main Activity must be public
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5
Start with the Layout:
activity_main.xml file
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6
res/layout/activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/button1"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#ff0000"
android:text="@string/red_prompt"/>
<Button
android:id="@+id/button2"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#0000ff"
android:text="@string/blue_prompt"/>
<Button
android:id="@+id/button3"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#ffff00"
android:text="@string/yellow_prompt"/>
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The first part of
activity_main.xml:
Starts the LinearLayout
7
res/layout/activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/button1"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#ff0000"
android:text="@string/red_prompt"/>
<Button
android:id="@+id/button2"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#0000ff"
android:text="@string/blue_prompt"/>
<Button
android:id="@+id/button3"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#ffff00"
android:text="@string/yellow_prompt"/>
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The first part of
activity_main.xml:
Starts the LinearLayout
Defines the 3 buttons
8
res/layout/activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/button1"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#ff0000"
android:text="@string/red_prompt"/>
<Button
android:id="@+id/button2"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#0000ff"
android:text="@string/blue_prompt"/>
<Button
android:id="@+id/button3"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:textColor="#ffff00"
android:text="@string/yellow_prompt"/>
9/27/2013
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The first part of
activity_main.xml:
Starts the LinearLayout
Defines the 3 buttons
Radio Button and the
Radio Group come next
9
res/layout/activity_main.xml
<RadioGroup
android:gravity="center_horizontal"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:orientation="horizontal">
<RadioButton
android:id="@+id/radio_button1"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/red_prompt"/>
<RadioButton
android:id="@+id/radio_button2"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/blue_prompt"/>
<RadioButton
android:id="@+id/radio_button3"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/yellow_prompt"/>
</RadioGroup>
<TextView
android:id="@+id/color_region"
android:layout_height="match_parent"
android:layout_width="match_parent"/>
</LinearLayout>
9/27/2013
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The RadioGroup: must
use the “group” object
so that only one button
can be selected at a time
10
res/layout/activity_main.xml
<RadioGroup
android:gravity="center_horizontal"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:orientation="horizontal">
<RadioButton
android:id="@+id/radio_button1"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/red_prompt"/>
<RadioButton
android:id="@+id/radio_button2"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/blue_prompt"/>
<RadioButton
android:id="@+id/radio_button3"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/yellow_prompt"/>
</RadioGroup>
<TextView
android:id="@+id/color_region"
android:layout_height="match_parent"
android:layout_width="match_parent"/>
</LinearLayout>
9/27/2013
http://www.coreservlets.com
The RadioGroup: must
use the “group” object
so that only one button
can be selected at a time
Then, each of the 3 radio
buttons are declared
11
res/layout/activity_main.xml
<RadioGroup
android:gravity="center_horizontal"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:orientation="horizontal">
<RadioButton
android:id="@+id/radio_button1"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/red_prompt"/>
<RadioButton
android:id="@+id/radio_button2"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/blue_prompt"/>
<RadioButton
android:id="@+id/radio_button3"
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:text="@string/yellow_prompt"/>
</RadioGroup>
<TextView
android:id="@+id/color_region"
android:layout_height="match_parent"
android:layout_width="match_parent"/>
</LinearLayout>
9/27/2013
http://www.coreservlets.com
The RadioGroup: must
use the “group” object
so that only one button
can be selected at a time
Then, each of the 3 radio
buttons are declared
Finally, the text view is
declared and then the
layout is complete
12
res/layout/activity_main.xml
• The App’s appearance
• No functionality yet
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13
res/layout/strings.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">Event Handling Example</string>
<string name="red_prompt">Red</string>
<string name="blue_prompt">Blue</string>
<string name="yellow_prompt">Yellow</string>
</resources>
The title of the App
It can easily be changed
just by editing this file
and then saving it
The text on each of the 3 buttons
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14
gen/packageName/R.java
• The main java file (Events1Example.java) will
use this file to find the IDs for each of the
objects
• This file is
automatically
generated by
Eclipse
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15
The Main Activity Class:
Events1Example.java
Has a separate Event Handler Class:
ColorSetter.java
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gen/packageName/Events1Example.java
The first part of Events1Example.java :
It extends Activity (makes
this a subclass of Activity so
@Override
that it inherits all of the
public void onCreate(Bundle savedInstanceState) {
Activity Class’s functionality)
super.onCreate(savedInstanceState);
public class Events1Example extends Activity {
private View mColorRegion;
setContentView(R.layout.main);
mColorRegion = findViewById(R.id.color_region);
Button b1 = (Button)findViewById(R.id.button1);
Button b2 = (Button)findViewById(R.id.button2);
Button b3 = (Button)findViewById(R.id.button3);
RadioButton r1 =
(RadioButton)findViewById(R.id.radio_button1);
RadioButton r2 =
(RadioButton)findViewById(R.id.radio_button2);
RadioButton r3 =
(RadioButton)findViewById(R.id.radio_button3
9/27/2013
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17
gen/packageName/Events1Example.java
The first part of Events1Example.java :
It extends Activity (makes
this a subclass of Activity so
@Override
that it inherits all of the
public void onCreate(Bundle savedInstanceState) {
Activity Class’s functionality)
super.onCreate(savedInstanceState);
public class Events1Example extends Activity {
private View mColorRegion;
setContentView(R.layout.main);
mColorRegion = findViewById(R.id.color_region);
Button b1 = (Button)findViewById(R.id.button1);
Button b2 = (Button)findViewById(R.id.button2);
Button b3 = (Button)findViewById(R.id.button3);
RadioButton r1 =
(RadioButton)findViewById(R.id.radio_button1);
RadioButton r2 =
(RadioButton)findViewById(R.id.radio_button2);
RadioButton r3 =
(RadioButton)findViewById(R.id.radio_button3
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It contains the onCreate ()
method required in the main
java class
http://www.coreservlets.com
18
gen/packageName/Events1Example.java
The first part of Events1Example.java :
public class Events1Example extends Activity {
private View mColorRegion;
It declares the content view
and color region (note that
it looks for the IDs in R.java)
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mColorRegion = findViewById(R.id.color_region);
Button b1 = (Button)findViewById(R.id.button1);
Button b2 = (Button)findViewById(R.id.button2);
Button b3 = (Button)findViewById(R.id.button3);
RadioButton r1 =
(RadioButton)findViewById(R.id.radio_button1);
RadioButton r2 =
(RadioButton)findViewById(R.id.radio_button2);
RadioButton r3 =
(RadioButton)findViewById(R.id.radio_button3
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19
gen/packageName/Events1Example.java
The first part of Events1Example.java :
public class Events1Example extends Activity {
private View mColorRegion;
It declares the content view
and color region (note that
it looks for the IDs in R.java)
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mColorRegion = findViewById(R.id.color_region);
Button b1 = (Button)findViewById(R.id.button1);
Button b2 = (Button)findViewById(R.id.button2);
Button b3 = (Button)findViewById(R.id.button3);
RadioButton r1 =
(RadioButton)findViewById(R.id.radio_button1);
RadioButton r2 =
(RadioButton)findViewById(R.id.radio_button2);
RadioButton r3 =
(RadioButton)findViewById(R.id.radio_button3
It finds the IDs for
the 3 buttons and
The 3 radio buttons
9/27/2013
It finds their IDs by referencing
the R.java file
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20
gen/packageName/Events1Example.java
The second part of Events1Example.java :
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED, this));
ColorSetter(Color.BLUE, this));
ColorSetter(Color.YELLOW, this));
ColorSetter(Color.RED, this));
ColorSetter(Color.BLUE, this));
ColorSetter(Color.YELLOW, this));
}
public void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
Assigns a class as the event
handler for each of the Buttons
and RadioButtons.
}
9/27/2013
http://www.coreservlets.com
21
gen/packageName/Events1Example.java
The second part of Events1Example.java :
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED, this));
ColorSetter(Color.BLUE, this));
ColorSetter(Color.YELLOW, this));
ColorSetter(Color.RED, this));
ColorSetter(Color.BLUE, this));
ColorSetter(Color.YELLOW, this));
}
public void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
}
You can pass arguments to the event handler (the colors)
so that the same event handler class can have different
behaviors for different controls (buttons and radioButtons)
9/27/2013
http://www.coreservlets.com
22
gen/packageName/Events1Example.java
The second part of Events1Example.java :
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED, this));
ColorSetter(Color.BLUE, this));
ColorSetter(Color.YELLOW, this));
ColorSetter(Color.RED, this));
ColorSetter(Color.BLUE, this));
ColorSetter(Color.YELLOW, this));
}
public void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
You have to pass a reference to the
main Activity (“this” above) so that
the event handler can call back to
code in that Activity.
}
9/27/2013
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23
gen/packageName/ColorSetter.java
The Event Handler Class:
public class ColorSetter implements OnClickListener {
private int regionColor;
private Events1Example mainActivity;
public ColorSetter(int regionColor,
Events1Example mainActivity) {
this.regionColor = regionColor;
this.mainActivity = mainActivity;
}
Event handler must
store a reference to
the main Activity so
that it can call back
to it.
@Override
public void onClick(View v) {
mainActivity.setRegionColor(regionColor);
}
}
9/27/2013
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24
gen/packageName/ColorSetter.java
The Event Handler Class:
public class ColorSetter implements OnClickListener {
private int regionColor;
private Events1Example mainActivity;
public ColorSetter(int regionColor,
Events1Example mainActivity) {
this.regionColor = regionColor;
this.mainActivity = mainActivity;
}
Event handler must
store a reference to
the main Activity so
that it can call back
to it.
@Override
public void onClick(View v) {
mainActivity.setRegionColor(regionColor);
}
}
Another option in this particular case would be to pass the TextView to
the event handler, but passing the main Activity is a more general solution.
9/27/2013
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25
Results on the Emulator
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26
The Main Activity Class Using a
Named Inner Class for Event
Handling
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The App
• Goal
– Change color of a TextView when Button or RadioButton
is pressed. Different colors depending on which pressed.
• Same App as previous example
• Approach
– Use an inner class that implements View.OnClickListener
• Advantages
– You can pass arguments to change behavior
– Event handler methods can access private data of
Activity. No reference is needed to call to Activity.
• Disadvantages
– Since Listener class is in same file as Activity, it is more
tightly coupled, and cannot be changed independently
9/27/2013
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28
XML Files:
Same as Previous Example
• res/layout/main.xml
– Defines vertical LinearLayout that contains 3
Buttons, a horizontal RadioGroup (with 3
RadioButtons), and a TextView.
– The Buttons, RadioButtons, and TextView have
IDs so that they can be referred to in the Java
code
• res/values/strings.xml
– Defines the app name and the labels of the
Buttons and RadioButtons
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Main Activity Class
public class Events2Example extends Activity {
private View mColorRegion;
Except for the class name, this
top part of the Activity is
exactly the same as the
previous example.
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mColorRegion = findViewById(R.id.color_region);
Button b1 = (Button)findViewById(R.id.button1);
Button b2 = (Button)findViewById(R.id.button2);
Button b3 = (Button)findViewById(R.id.button3);
RadioButton r1 =
(RadioButton)findViewById(R.id.radio_button1);
RadioButton r2 =
(RadioButton)findViewById(R.id.radio_button2);
RadioButton r3 =
(RadioButton)findViewById(R.id.radio_button3);
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Main Activity Class
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
}
private void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
9/27/2013
http://www.coreservlets.com
Assigns an inner class as
the event handler for
each of the Buttons and
RadioButtons.
31
Main Activity Class
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
}
private void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
Assigns an inner class as
the event handler for
each of the Buttons and
RadioButtons.
As with the previous example, you can
pass arguments to the event handler
(the colors) so that the same event
handler class can have different
behaviors for different controls
9/27/2013
http://www.coreservlets.com
32
Main Activity Class
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
}
private void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
As with the previous example, you can
pass arguments to the event handler
(the colors) so that the same event
handler class can have different
behaviors for different controls
9/27/2013
http://www.coreservlets.com
Assigns an inner class as
the event handler for
each of the Buttons and
RadioButtons.
Since the event handler is in
the same class, you do not
have to supply a reference to
the main Activity class.
33
Main Activity Class
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
}
private void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
Note no closing brace. This
class is not finished yet
(continued on next slide)
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Since this method will only
be called by the method in
inner event handler class, it
is allowed to be private.
34
Main Activity Class
private class ColorSetter implements OnClickListener {
private int regionColor;
public ColorSetter(int regionColor) {
this.regionColor = regionColor;
}
@Override
public void onClick(View v) {
setRegionColor(regionColor);
}
}
}
Event handler can directly
call methods in the main
activity, even if the method
is private.
Closes the class
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35
Results on the Emulator
Results are the same as
the previous example
9/27/2013
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36
The Main Activity Class Using an
Anonymous Inner Class (AIC) for
Event Handling
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Main Activity Class
public class Events2Example extends Activity {
private View mColorRegion;
Except for the class name, this
top part of the Activity is
exactly the same as the
previous example.
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mColorRegion = findViewById(R.id.color_region);
Button b1 = (Button)findViewById(R.id.button1);
Button b2 = (Button)findViewById(R.id.button2);
Button b3 = (Button)findViewById(R.id.button3);
RadioButton r1 =
(RadioButton)findViewById(R.id.radio_button1);
RadioButton r2 =
(RadioButton)findViewById(R.id.radio_button2);
RadioButton r3 =
(RadioButton)findViewById(R.id.radio_button3);
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Original Main Activity Class
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
}
private void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
9/27/2013
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In the original Main Activity
Class, we called an event
handler inner class (an
onClickListener) for each
button and passed data into
it
39
Original Main Activity Class
b1.setOnClickListener(new
b2.setOnClickListener(new
b3.setOnClickListener(new
r1.setOnClickListener(new
r2.setOnClickListener(new
r3.setOnClickListener(new
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
ColorSetter(Color.RED));
ColorSetter(Color.BLUE));
ColorSetter(Color.YELLOW));
}
private void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
In the original Main Activity
Class, we called an event
handler inner class (an
onClickListener) for each
button and passed data into
it
Then, the event handler
called this method to change
the color of the view area
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40
NEW Main Activity Class
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
The part in RED is the new
public void onClick(View v) {
setRegionColor(Color.RED);
part: the anonymous inner
}
class
});
b2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.BLUE);
}
});
b3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.YELLOW);
}
});
9/27/2013
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41
Comparying Separate Classes and AICs
private class ColorSetter implements OnClickListener {
private int regionColor;
This is an example of an
@Override
public void onClick(View v) {
Event Handling Class declaration
setRegionColor(regionColor);
}
}
b1.set.OnClickListener(EventHandlingClass);
b1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.RED);
}
});
9/27/2013
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42
Comparying Separate Classes and AICs
private class ColorSetter implements OnClickListener {
private int regionColor;
This is an example of an
@Override
public void onClick(View v) {
Event Handling Class declaration
setRegionColor(regionColor);
}
This an example of assigning the
}
b1.set.OnClickListener(EventHandlingClass);
Event Handling Class to a button
b1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.RED);
}
});
9/27/2013
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43
Comparying Separate Classes and AICs
private class ColorSetter implements OnClickListener {
private int regionColor;
@Override
public void onClick(View v) {
setRegionColor(regionColor);
Between the parentheses is the
}
Event Handling Class followed by
}
b1.set.OnClickListener(EventHandlingClass);
a semicolon specifying the end
of the statement
b1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.RED);
}
});
9/27/2013
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44
Comparying Separate Classes and AICs
private class ColorSetter implements OnClickListener {
private int regionColor;
@Override
public void onClick(View v) {
setRegionColor(regionColor);
Then, the implementation of the
}
class is between the braces
}
b1.set.OnClickListener(EventHandlingClass);
b1.setOnClickListener (new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.RED);
}
});
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Comparying Separate Classes and AICs
private class ColorSetter implements OnClickListener {
private int regionColor;
@Override
public void onClick(View v) {
setRegionColor(regionColor);
The implementation of the
}
onClick () method is between
}
these braces
b1.set.OnClickListener(EventHandlingClass);
b1.setOnClickListener (new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.RED);
}
});
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Comparying Separate Classes and AICs
private class ColorSetter implements OnClickListener {
private int regionColor;
@Override
public void onClick(View v) {
setRegionColor(regionColor);
The statements of the onClick
}
method are the same (if you
}
b1.set.OnClickListener(EventHandlingClass);
()
replaced the variable regionColor)
with a constant color definition
b1.setOnClickListener (new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.RED);
}
});
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Back to the New Main Activity Class
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
So, the part in RED is the
public void onClick(View v) {
setRegionColor(Color.RED);
anonymous inner class
}
});
b2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.BLUE);
}
});
b3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.YELLOW);
}
});
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NEW Main Activity Class
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
The part in RED is the
public void onClick(View v) {
setRegionColor(Color.RED);
anonymous inner class
}
});
b2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.BLUE);
Each AIC is identical except
}
for the color passed to the
});
b3.setOnClickListener(new OnClickListener() {method setRegionColor()
@Override
public void onClick(View v) {
setRegionColor(Color.YELLOW);
}
});
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NEW Main Activity Class
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
The anonymous inner class
public void onClick(View v) {
setRegionColor(Color.RED);
is declared here.
}
});
b2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.BLUE);
}
});
b3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.YELLOW);
}
});
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NEW Main Activity Class
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
The anonymous inner class
public void onClick(View v) {
setRegionColor(Color.RED);
is declared here.
}
});
We’ve called a new
b2.setOnClickListener(new OnClickListener() {
onClickListener, but didn’t
@Override
public void onClick(View v) {
name it.
setRegionColor(Color.BLUE);
}
});
b3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.YELLOW);
}
});
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NEW Main Activity Class
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
The anonymous inner class
public void onClick(View v) {
setRegionColor(Color.RED);
is declared here.
}
});
We’ve called a new
b2.setOnClickListener(new OnClickListener() {
onClickListener, but didn’t
@Override
public void onClick(View v) {
name it.
setRegionColor(Color.BLUE);
}
But, we did declare how to
});
b3.setOnClickListener(new OnClickListener() {
handle the event for that
@Override
Button
public void onClick(View v) {
setRegionColor(Color.YELLOW);
}
});
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NEW Main Activity Class
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
The anonymous inner class
public void onClick(View v) {
setRegionColor(Color.RED);
is declared here.
}
});
We’ve called a new
b2.setOnClickListener(new OnClickListener() {
onClickListener, but didn’t
@Override
public void onClick(View v) {
name it.
setRegionColor(Color.BLUE);
}
But, we did declare how to
});
b3.setOnClickListener(new OnClickListener() {
handle the event for that
@Override
Button
public void onClick(View v) {
setRegionColor(Color.YELLOW);
And it is right here:
}
});
Obviously associated with
the button
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NEW Main Activity Class
Uses an Anonymous Inner Class for each button
r1.setOnClickListener(new OnClickListener() {
@Override
The radio buttons use the
public void onClick(View v) {
setRegionColor(Color.RED);
same AIC (except for color)
}
});
r2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.BLUE);
Each calls the method
}
setRegionColor()
});
r3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.YELLOW);
}
});
}
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This is the setRegionColor() method
/** Sets the color of the color region. */
private void setRegionColor(int color) {
mColorRegion.setBackgroundColor(color);
}
}
This worked exactly the same
as the two previous approaches
• In this case, the AICs were redundant since
each button was supposed to do the same
thing.
• Each AIC called the setRegionColor() method
• Why not just put this inside each of the
AICs?
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Advantages and Disadvantages
• There are some disadvantages:
– Each AIC was exactly the same except for the color
• So there was a lot of redundancy
• It may need more memory than is available
– Possible but unlikely
– Parameters can not be passed to the AICs
– The android:onClick attribute cannot be used in XML file
(not that that is so important)
• Advantages:
– The event handler is at the same place as the button (in
the code)
– Easy to see that the two are associated
– You don’t have to search through code for the handler
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Results on the Emulator
Results are the same as
the previous examples
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One more change: delete the
setRegionColor() method
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Remove the setRegionColor() method
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
Each AIC calls the
public void onClick(View v) {
setRegionColor(Color.RED);
setRegionColor() method
}
change the color of the
});
text view
b2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.BLUE);
}
});
b3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setRegionColor(Color.YELLOW);
}
});
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to
59
Remove the setRegionColor() method
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mColorRegion.setBackgroundColor(Color.RED);
}
});
b2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mColorRegion.setBackgroundColor(Color.BLUE);
}
});
b3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mColorRegion.setBackgroundColor(Color.YELLOW);
}
});
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Each AIC calls the
setRegionColor() method to
change the color of the
text view
But, why not change the
color here instead of calling
a separate method
60
Remove the setRegionColor() method
Uses an Anonymous Inner Class for each button
b1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mColorRegion.setBackgroundColor(Color.RED);
}
});
b2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mColorRegion.setBackgroundColor(Color.BLUE);
}
});
b3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mColorRegion.setBackgroundColor(Color.YELLOW);
}
});
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http://www.coreservlets.com
Each AIC calls the
setRegionColor() method to
change the color of the
text view
But, why not change the
color here instead of calling
a separate method
So each of the AICs was
changed and the
setRegionColor() method
was deleted
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Results on the Emulator
And, of course, the results
are the same as the
previous examples
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Summary
• Developed an App to change the colors of the
main screen (a TextView)
• Used three approaches
– The first used a separate Listener class
– The second used a named inner class
– The third used an anonymous inner class
• All approaches worked well with multiple
controls
– Using the same event handler
– But passing parameters (like the color) into it
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Summary (continued)
• I prefer the Anonymous Inner Class method,
when it can be used
– It is obviously the event handler for the button
where it is declared
– It is easy to find if code needs to be changed
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