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);
}
}