Android開發入門（九）用戶界面 9.3 注冊事件監聽器

當用戶與視圖views進行交互的時候，views也會觸發事件。舉個例子，當用戶點擊了一個按鈕，你需要為 這個事件服務，只有這樣，才能去執行某些適當的行為。如果想這麼做的話，你就需要為視圖views注冊監聽 。

使用上一節中的例子，在activity中有兩個Button。我們可以使用一個匿名的類，為按鈕設置點擊 事件。

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);    
               
        //---the two buttons are wired to the same event handler---    
        Button btn1 = (Button)findViewById(R.id.btn1);    
        btn1.setOnClickListener(btnListener);    
               
        Button btn2 = (Button)findViewById(R.id.btn2);    
        btn2.setOnClickListener(btnListener);    
    }    
           
    //---create an anonymous class to act as a button click listener---    
    private OnClickListener btnListener = new OnClickListener()    
    {    
        public void onClick(View v)    
        {    
            Toast.makeText(getBaseContext(),    
                    ((Button) v).getText() + " was clicked",    
                    Toast.LENGTH_LONG).show();    
        }    
    };    
           
    @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;    
    }    
       
}

如果你點擊了OK按鈕或Cancel按鈕，對應的消息就會出現在屏幕上，這也就說明了，適當的事件 被出發了。

除了定義一個匿名類，也可以定一個匿名內部類去處理事件。下面的例子展示如何 處理EditText的onFocusChange()方法。

//---create an anonymous inner class to act as an 

onfocus listener---    
EditText txt1 = (EditText)findViewById(R.id.txt1);    
txt1.setOnFocusChangeListener(new View.OnFocusChangeListener()    
{    
    @Override 
    public void onFocusChange(View v, boolean hasFocus) {    
        Toast.makeText(getBaseContext(),    
            ((EditText) v).getId() + " has focus - " + hasFocus,    
            Toast.LENGTH_LONG).show();    
    }    
});