Android笔记二十四.Android基于回调的事件处理机制

package com.example.android_event2;
import android.content.Context;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.widget.Button;
import android.widget.Toast;
public class MyButton extends Button
{
 //构造方法
 public MyButton(Context context, AttributeSet attrs) {
  super(context, attrs);
 }
 //回调方法
 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
   super.onKeyDown(keyCode, event);
   Toast.makeText(getContext(),"您按下了数字："+keyCode,Toast.LENGTH_SHORT).show();
   return true;	//返回true,表明该事件不会向外扩散
 }
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
   <!--方法一：在XML布局文件中创建组件-->
    <com.example.android_event2.MyButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="回调测试" />
</LinearLayout>
(3)MainActivity.java：主Activity
package com.example.android_event2;
import android.app.Activity;
import android.os.Bundle;
public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //方法二：Java代码中配置自定义组件
    }
}

package com.example.android_event2;
import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnKeyListener;
import android.widget.Button;
public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //采用监听模式
        Button myButton = (Button)findViewById(R.id.btn);
        myButton.setOnKeyListener(new OnKeyListener(){
   public boolean onKey(View v, int keyCode, KeyEvent event) {
    System.out.println("组件所绑定的事件监听器被触发");
    return false;
   }
         
        });
    }
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
       super.onKeyDown(keyCode, event);
       System.out.println("该组件所在的Activity的回调方法onKeyDown被调用");
       return false;	//返回true,表明该事件不会向外扩散
    }
}

package com.example.android_event2;
import android.content.Context;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.widget.Button;
public class MyButton extends Button
{
 //构造方法
 public MyButton(Context context, AttributeSet attrs) {
  super(context, attrs);
 }
 //回调方法
 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
   super.onKeyDown(keyCode, event);
   System.out.println("自定义组件中的回调方法onKeyDown被调用");
   return false;	//返回true,表明该事件不会向外扩散
 }
}

package com.example.android_event2;
import android.content.Context;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.widget.Button;
public class MyButton extends Button
{
 //构造方法
 public MyButton(Context context, AttributeSet attrs) {
  super(context, attrs);
 }
 //回调方法
 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
   super.onKeyDown(keyCode, event);
   System.out.println("自定义组件中的回调方法onKeyDown被调用");
   return false;	//返回true,表明该事件不会向外扩散
 }
}

package com.example.android_event3;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends Activity {
 private EditText text;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        text = (EditText)findViewById(R.id.result);
    }
    //将clickHandler方法直接绑定到标签
    public void clickHandler(View source)
    {
     text.setText("中华人民共和国万岁！");
    }
}

<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:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:text="单击我"
     android:onClick="clickHandler"/>
 <EditText
     android:id="@+id/result"
     android:inputType="none"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"/>
</LinearLayout>