Android 中的接口回调

  在Android中到处可见接口回调机制,尤其是UI事件处理方面。举一个最常见的例子button点击事件,button有一个点击方法onClick(),我们知道onclick()是一个回调方法,当用户点击button就执行这个方法。在源码中是这样定义的:

//这个是View的一个回调接口  
/**  
* 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);  
}  

 下面看一个简单的例子:

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;  
  
public class MainActivity extends Activity implements OnClickListener{  
  
     private Button button;  
  
     @Override  
     public void onCreate(Bundle savedInstanceState) {  
          super.onCreate(savedInstanceState);  
          setContentView(R.layout.activity_main);  
          button = (Button)findViewById(R.id.button1);  
            
          
          button.setOnClickListener(this);  
     }  
  
     @Override  
     public void onClick(View v) {  
          Toast.makeText(getApplication(), "OnClick", Toast.LENGTH_LONG).show();  
     }  
  
}  
    这就是一个很典型的例子,当然也可以这样写:  
import android.app.Activity;  
import android.os.Bundle;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Button;  
  
public class SSSS extends Activity {  
  
     private Button button;  
     private OnClickListener clickListener = new OnClickListener() {  
  
          @Override  
          public void onClick(View v) {  
               // TODO Auto-generated method stub  
  
          }  
     };  
  
     @Override  
     protected void onCreate(Bundle savedInstanceState) {  
          // TODO Auto-generated method stub  
          super.onCreate(savedInstanceState);  
          button = (Button)findViewById(R.id.button1);  
          button.setOnClickListener(clickListener);    
     }  
  
}  

下面是View类的setOnClickListener方法,把和回调相关代码贴出来。什么贴它呢,因为Button继承于TextView,而TextView继承于View,在View里面处理的回调:

/**  
*  
*/  
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;  
     
    /**  
     *  
     * 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);  
             
            mOnClickListener.onClick(this);  
            return true;  
        }  
  
        return false;  
    }  
}  
那现在一起来总结一下基本的回调是如何实现的,首先创建一个接口,这个接口用于你在某个情景下执行相应的操作。接着创建一个功能类,比如这个类可以显示一个对话框、可以滑动菜单、可以下载数据等等。然后,在这个类里面声明回调接口的对象,之后在这个类里面创建在某个情景下需要执行的方法,而且在这个方法里面为声明的接口对象赋值。最后在其他的类中使用这个功能类就可以了。所以说,最少也是需要三个类共同来完成这个回调机制。
    这下大家应该就比较明白了,那我们就自己按照这个方式和流程完成一个这样的例子。以Dialog为例,一般我们在开发时候,经常会用到Dialog。比如一个弹出框,里面有确认和取消。通常情况下,我们可能会这样写:
final Dialog dialog = new Dialog(this, R.style.MyDialogStyle);  
         dialog.setContentView(R.layout.dialog_exit_train);  
         dialog.show();  
         ImageButton ib_affirm = (ImageButton) dialog  
                   .findViewById(R.id.dialog_exit_ib_affirm);  
         ImageButton ib_cancel = (ImageButton) dialog  
                   .findViewById(R.id.dialog_exit_ib_cancel);  
  
         ib_affirm.setOnClickListener(new View.OnClickListener() {  
  
              @Override  
              public void onClick(View v) {  
  
                   saveUserData();  
                   dialog.dismiss();  
                   TestActivity.this.finish();  
              }  
         });  
  
         ib_cancel.setOnClickListener(new View.OnClickListener() {  
  
              @Override  
              public void onClick(View v) {  
  
                   dialog.dismiss();  
              }  
         });  

也就是得到点击对象之后再去调用onClick(),这样有一个缺点就是你每次都要写,不利于重复使用。那我们就可以对此进行一个封装,看代码:

import android.app.Dialog;  
import android.content.Context;  
import android.os.Bundle;  
import android.text.TextPaint;  
import android.view.View;  
import android.view.Window;  
import android.view.WindowManager;  
import android.widget.Button;  
import android.widget.TextView;  
  
import com.fanfou.app.opensource.R;  
  
/**  
*   
*  
*/  
public class AlertInfoDialog extends Dialog implements View.OnClickListener {  
    //创建接口  
    public static interface OnOKClickListener {  
        public void onOKClick();  
    }  
  
    private final Context mContext;  
    private TextView mTitleView;  
    private TextView mTextView;  
  
    private Button mButtonOk;  
    private CharSequence mTitle;  
  
    private CharSequence mText;  
    //生命接口对象  
    private OnOKClickListener mClickListener;  
  
    public AlertInfoDialog(final Context context, final String title,  
            final String text) {  
        super(context, R.style.Dialog);  
        this.mContext = context;  
        this.mTitle = title;  
        this.mText = text;  
    }  
  
    private void init() {  
        setContentView(R.layout.dialog_alert);  
  
        this.mTitleView = (TextView) findViewById(R.id.title);  
        final TextPaint tp = this.mTitleView.getPaint();  
        tp.setFakeBoldText(true);  
        this.mTitleView.setText(this.mTitle);  
  
        this.mTextView = (TextView) findViewById(R.id.text);  
        this.mTextView.setText(this.mText);  
  
        this.mButtonOk = (Button) findViewById(R.id.button_ok);  
        this.mButtonOk.setOnClickListener(this);  
  
    }  
  
    @Override  
    public void onClick(final View v) {  
        final int id = v.getId();  
        switch (id) {  
        case R.id.button_ok:  
            cancel();//调用  
            if (this.mClickListener != null) {  
                this.mClickListener.onOKClick();  
            }  
            break;  
        default:  
            break;  
        }  
    }  
  
    @Override  
    protected void onCreate(final Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setBlurEffect();  
        init();  
    }  
  
    protected void setBlurEffect() {  
        final Window window = getWindow();  
        final WindowManager.LayoutParams lp = window.getAttributes();  
        // lp.alpha=0.8f;  
        lp.dimAmount = 0.6f;  
        window.setAttributes(lp);  
        window.addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);  
        // window.addFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND);  
    }  
  
    public void setMessage(final CharSequence message) {  
        this.mText = message;  
        this.mTextView.setText(this.mText);  
    }  
  
    public void setMessage(final int resId) {  
        this.mText = this.mContext.getResources().getText(resId);  
        this.mTextView.setText(this.mText);  
    }  
    //设置监听器 也就是实例化接口  
    public void setOnClickListener(final OnOKClickListener clickListener) {  
        this.mClickListener = clickListener;  
    }  
  
    @Override  
    public void setTitle(final CharSequence title) {  
        this.mTitle = title;  
        this.mTitleView.setText(this.mTitle);  
    }  
  
    @Override  
    public void setTitle(final int resId) {  
        this.mTitle = this.mContext.getResources().getText(resId);  
        this.mTitleView.setText(this.mTitle);  
    }  
  
}  

  方式和上面介绍的一样,感兴趣的朋友可以自己去实现其他效果的。