Android 程式开发：（九）用户界面 —— 9.3 注册事件监听器

当用户与视图views进行交互的时候，views也会触发事件。举个例子，当用户点击了一个按钮，你需要为这个事件服务，只有这样，才能去执行某些适当的行为。如果想这么做的话，你就需要为视图views注册监听。

使用上一节中的例子，在activity中有两个Button。我们可以使用一个匿名的类，为按钮设置点击事件。

[java]
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);

        //---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;
    }

}
如果你点击了OK按钮或Cancel按钮，对应的消息就会出现在屏幕上，这也就说明了，适当的事件被出发了。

除了定义一个匿名类，也可以定一个匿名内部类去处理事件。下面的例子展示如何处理EditText的onFocusChange()方法。

[java]
//---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) {

补充：移动开发 , Android ,