Android 中的接口回调

  版本:1.0
  日期:2014.3.25
  版权:© 2014 kince 转载注明出处


  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。
  






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Android 中的接口回调

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