Android 中的接口回调

http://blog.csdn.net/wangjinyu501/article/details/22052187

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：

[html] view
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//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：

[html] view
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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：

[html] view
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/**

*

*/

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：

[html] view
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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：

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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。