現在來分析分析下Android View的點擊方法onclick（）;我們知道onclick()是一個回調方法，當用戶點擊View就執行這個方法，我們用Button來舉例好了
//這個是View的一個回調接口
/**
* Interface definition for a callback to be invoked when a view is clicked.
*/
public interface OnClickListener {
/**
* Called when a view has been clicked.
*
* @param v The view that was clicked.
*/
void onClick(View v);
}
package com.example.demoactivity;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
/**
* 這個就相當於Class A
* @author xiaanming
* 實現了 OnClickListener接口---->背景一
*/
public class MainActivity extends Activity implements OnClickListener{
/**
* Class A 包含Class B的引用----->背景二
*/
private Button button;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button)findViewById(R.id.button1);
/**
* Class A 調用View的方法,而Button extends View----->A類調用B類的某個方法 C
*/
button.setOnClickListener(this);
}
/**
* 用戶點擊Button時調用的回調函數，你可以做你要做的事
* 這里我做的是用Toast提示OnClick
*/
@Override
public void onClick(View v) {
Toast.makeText(getApplication(), "OnClick", Toast.LENGTH_LONG).show();
}
}
下面是View類的setOnClickListener方法，就相當於B類咯，只把關鍵代碼貼出來
/**
* 這個View就相當於B類
* @author xiaanming
*
*/
public class View implements Drawable.Callback, KeyEvent.Callback, AccessibilityEventSource {
/**
* Listener used to dispatch click events.
* This field should be made private, so it is hidden from the SDK.
* {@hide}
*/
protected OnClickListener mOnClickListener;
/**
* setOnClickListener()的參數是OnClickListener接口------>背景三
* Register a callback to be invoked when this view is clicked. If this view is not
* clickable, it becomes clickable.
*
* @param l The callback that will run
*
* @see #setClickable(boolean)
*/
public void setOnClickListener(OnClickListener l) {
if (!isClickable()) {
setClickable(true);
}
mOnClickListener = l;
}
/**
* Call this view's OnClickListener, if it is defined.
*
* @return True there was an assigned OnClickListener that was called, false
* otherwise is returned.
*/
public boolean performClick() {
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
if (mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
//這個不就是相當於B類調用A類的某個方法D，這個D就是所謂的回調方法咯
mOnClickListener.onClick(this);
return true;
}
return false;
}
}
這個例子就是Android典型的回調機制，看完這個你是不是更進一步的理解了回調機制呢？ 線程run()也是一個回調方法，當執行Thread的start（）方法就會回調這個run()方法，還有處理消息都比較經典等等