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Download Lecture 19 Introduction to Android User Interface (UI) By Shinping R. Wang
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Lecture 19 Introduction to Android User Interface (UI) By Shinping R. Wang CSIE Dept. of Da‐yeh University Note A “what is” introduction Avoids covering too much detail. Reference The following discussion is excerpted from 1. Android Developer: http://developer.android.com/guide/topics/ui/index.html 2. Android Resources: http://developer.android.com/resources/samples/ApiDemos/ src/com/example/android/apis/app/index.html#Activity View & ViewGroup View class/object Is a data structure whose properties defined layout and contents of a specific rectangular area in the screen. handles its own measurement, layout, drawing, focus change, scrolling, and key/gesture interactions of the user to itself. View & ViewGroup ViewGroup class serves as the base for subclasses called "layouts“ kinds of layout: Linear, Tabular, Relative, and etc… View Hierarchy A UI is a tree like hierarchy of Views View objects are leaves in the tree, ViewGroup objects are branches in the tree For Example http://developer.android.com/images/viewgroup.png Android design methodology Logic and UI are designed separately, Logic – using Java UI - using xml View Hierarchy setContentView() In order to attach the view hierarchy tree to the screen for rendering, your Activity(logic) must call the setContentView() method and pass a reference to the root node object. http://developer.android.com/images/viewgroup.png View Hierarchy The Android system receives this reference and uses it to invalidate, measure, and draw the tree. View Hierarchy The root node of the hierarchy requests that its child nodes draw themselves — in turn, each view group node is responsible for calling upon each of its own child views to draw themselves. Layout <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:id="@+id/text" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello, I am a TextView" /> <Button android:id="@+id/button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello, I am a Button" /> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" : </LinearLayout> </LinearLayout> Layout Pre-defined view groups offered by Android (called layouts) include LinearLayout, RelativeLayout, TableLayout, GridLayout and others. Widgets A widget Is a View object that serves as an interface for interaction with the user. Can be pre-built buttons, checkboxes, text-entry fields, date picker, and more. See http://developer.android.com/reference/android/widget/packagesummary.html Input Events There are two ways to sense and respond to user input events, Overriding defined event callback methods of class View a.k.a. Event Handlers scheme User defined callback methods using listener which is more commonly use a.k.a. Event listeners scheme. Input Events (Event Handler) Overriding defined event callback methods of class View Adapted when you've implemented your own View class and want to listen for specific events that occur within it. For example onKeyDown(int, KeyEvent) - Called when a new key event occurs. onKeyUp(int, KeyEvent) - Called when a key up event occurs. onTrackballEvent(MotionEvent) - Called when a trackball motion event occurs. onTouchEvent(MotionEvent) - Called when a touch screen motion event occurs. onFocusChanged(boolean, int, Rect) - Called when the view gains or loses focus. Input Events Event Listeners User defined callback methods using listener which is more commonly use. Implementing the pre-defined interface, Defined the corresponding callback methods, Register the callback methods to the interface. Input Events Event Listeners In a view object, you need to do one of two things: Define an event listener and register it with the View. On<something>Listener and the corresponding callback method On<something>() Input Events Event Listeners For example: The interface the registration the call back method View.OnClickListener setOnClickListener() onClick() View.OnTouchListener setOnTouchListener() onTouch() View.OnKeyListener setOnKeyListener() onKey() Advanced Topics Adapters AdapterView object is an implementation of ViewGroup that determines its child views based on a given Adapter object. Adapter acts like a courier between your data source (perhaps an array of external strings) and the AdapterView Building layouts with an adapter Adapter and AdapterView Adapter binds data to its layout where layout is a subclass of the class AdapterView. Building layouts with an adapter Adapter and AdapterView You use different Adapter for different AdapterView For example, an ArrayAdapter[T] for Spinner Advanced Topics Styles and Themes Style is a set of one or more formatting attributes that you can apply as a unit to individual elements in your layout. theme is a set of one or more formatting attributes that you can apply as a unit to all activities in an application, or just a single activity.
