Android 程式开发：（十一）监听UI事件 —— 11.1重写Activity中的方法

 

用户可以使用两种级别与你的UI进行交互，一种是activity级别，另一种是view级别。在activity级别，Activity类暴露了一些你可以重写的方法。有一些常用的方法，你可以在你的Activity中进行重写：

• onKeyDown
• onKeyUp
• onMenuItemSelected
• onMenuOpened
  

下面的例子重写了一些在activity中的方法，通过这个例子展示用户如何与众多的activity进行交互。

1、创建一个工程：UIActivity。

2、main.xml中的代码。

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1. <?xmlversion="1.0"encoding="utf-8"?> 
2. <LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android" 
3.     android:layout_width="fill_parent" 
4.     android:layout_height="fill_parent" 
5.     android:orientation="vertical"> 
6.  
7.     <TextView 
8.         android:layout_width="214dp" 
9.         android:layout_height="wrap_content" 
10.         android:text="Your Name" 
11.         /> 
12.     <EditText 
13.         android:id="@+id/txt1" 
14.         android:layout_width="214dp" 
15.         android:layout_height="wrap_content" 
16.         /> 
17.     <Button 
18.         android:id="@+id/btn1" 
19.         android:layout_width="106dp" 
20.         android:layout_height="wrap_content" 
21.         android:text="OK" 
22.         /> 
23.     <Button 
24.         android:id="@+id/btn2" 
25.         android:layout_width="106dp" 
26.         android:layout_height="wrap_content" 
27.         android:text="Cancel" 
28.         /> 
29.  
30. </LinearLayout> 

<?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:layout_width="214dp" android:layout_height="wrap_content" android:text="Your Name" /> <EditText android:id="@+id/txt1" android:layout_width="214dp" android:layout_height="wrap_content" /> <Button android:id="@+id/btn1" android:layout_width="106dp" android:layout_height="wrap_content" android:text="OK" /> <Button android:id="@+id/btn2" android:layout_width="106dp" android:layout_height="wrap_content" android:text="Cancel" /></LinearLayout>3、UIActivityActivity.java中的代码。

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1. package net.learn2develop.UIActivity; 
2.  
3. import android.app.Activity; 
4. import android.os.Bundle; 
5. import android.view.KeyEvent; 
6. import android.view.View; 
7. import android.view.View.OnClickListener; 
8. import android.widget.Button; 
9. import android.widget.EditText; 
10. import android.widget.Toast; 
11.  
12. public class UIActivityActivityextends Activity { 
13.     /** Called when the activity is first created. */ 
14.     @Override 
15.     public void onCreate(Bundle savedInstanceState) { 
16.         super.onCreate(savedInstanceState); 
17.         setContentView(R.layout.main); 
18.        
19.     } 
20.      
21.     @Override 
22.     public boolean onKeyDown(int keyCode, KeyEvent event) 
23.     { 
24.         switch (keyCode) 
25.         { 
26.             case KeyEvent.KEYCODE_DPAD_CENTER: 
27.                 Toast.makeText(getBaseContext(), 
28.                         "Center was clicked", 
29.                         Toast.LENGTH_LONG).show(); 
30.                 break;                 
31.             case KeyEvent.KEYCODE_DPAD_LEFT: 
32.                 Toast.makeText(getBaseContext(), 
33.                         "Left arrow was clicked", 
34.                         Toast.LENGTH_LONG).show(); 
35.                 break;                 
36.             case KeyEvent.KEYCODE_DPAD_RIGHT: 
37.                 Toast.makeText(getBaseContext(), 
38.                         "Right arrow was clicked", 
39.                         Toast.LENGTH_LONG).show(); 
40.                 break;                 
41.             case KeyEvent.KEYCODE_DPAD_UP: 
42.                 Toast.makeText(getBaseContext(), 
43.                         "Up arrow was clicked", 
44.                         Toast.LENGTH_LONG).show(); 
45.                 break; 
46.             case KeyEvent.KEYCODE_DPAD_DOWN: 
47.                 Toast.makeText(getBaseContext(), 
48.                         "Down arrow was clicked", 
49.                         Toast.LENGTH_LONG).show(); 
50.                 break;                 
51.         } 
52.         return false; 
53.     } 
54.  
55. } 

package net.learn2develop.UIActivity;import android.app.Activity;import android.os.Bundle;import android.view.KeyEvent;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;public class UIActivityActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { switch (keyCode) { case KeyEvent.KEYCODE_DPAD_CENTER: Toast.makeText(getBaseContext(), "Center was clicked", Toast.LENGTH_LONG).show(); break; case KeyEvent.KEYCODE_DPAD_LEFT: Toast.makeText(getBaseContext(), "Left arrow was clicked", Toast.LENGTH_LONG).show(); break; case KeyEvent.KEYCODE_DPAD_RIGHT: Toast.makeText(getBaseContext(), "Right arrow was clicked", Toast.LENGTH_LONG).show(); break; case KeyEvent.KEYCODE_DPAD_UP: Toast.makeText(getBaseContext(), "Up arrow was clicked", Toast.LENGTH_LONG).show(); break; case KeyEvent.KEYCODE_DPAD_DOWN: Toast.makeText(getBaseContext(), "Down arrow was clicked", Toast.LENGTH_LONG).show(); break; } return false; }}4、按F11调试。

5、当这个activity被加载，在EditText中输入一些文字。然后，点击方向键中的向下的按钮。观察屏幕上的信息。