接口回调机制详解-优快云博客

在java组件编程时(如Android编程)时会十分频繁的使用到接口回调，以前我都没有发现，只是照着书上写的做。最常见的就是View.setonClickListener(new View.onClickListener())这样的语句了。因为最近看得代码也渐渐多起来了，所以很自然的就发现这个问题了，然后还好现在Android中的sdk源码都是可以直接查看的，现在我明白了。

感觉接口回调也是一种多态的表现，过程就像View类中实现了onClickListener接口，即实现了onClickListener中的onClick方法。不过这个onClick方法只是一个空方法，我们使用一个继承自View的组件，如Button时，在为其注册onClickListener事件的过程中定义了具体的onClick实现方法。

其实对于接口回调的思考是源自opensudoku代码，下面是其中的代码片段：

Java代码

private static class FolderListViewBinder implements ViewBinder {
private Context mContext;
private FolderDetailLoader mDetailLoader;
public FolderListViewBinder(Context context) {
mContext = context;
mDetailLoader = new FolderDetailLoader(context);
}
@Override
public boolean setViewValue(View view, Cursor c, int columnIndex) {
switch (view.getId()) {
case R.id.name:
((TextView)view).setText(c.getString(columnIndex));
break;
case R.id.detail:
final long folderID = c.getLong(columnIndex);
final TextView detailView = (TextView)view;
detailView.setText(mContext.getString(R.string.loading));
mDetailLoader.loadDetailAsync(folderID, new FolderDetailCallback() {
@Override
public void onLoaded(FolderInfo folderInfo) {
if (folderInfo != null)
detailView.setText(folderInfo.getDetail(mContext));
}
});
}
return true;
}
public void destroy() {
mDetailLoader.destroy();
}
}

private static class FolderListViewBinder implements ViewBinder {
		private Context mContext;
		private FolderDetailLoader mDetailLoader;
		
		
		public FolderListViewBinder(Context context) {
			mContext = context;
			mDetailLoader = new FolderDetailLoader(context);
		}
		
		@Override
		public boolean setViewValue(View view, Cursor c, int columnIndex) {

			switch (view.getId()) {
			case R.id.name:
				((TextView)view).setText(c.getString(columnIndex));
				break;
			case R.id.detail:
				final long folderID = c.getLong(columnIndex);
				final TextView detailView = (TextView)view;
				detailView.setText(mContext.getString(R.string.loading));
				mDetailLoader.loadDetailAsync(folderID, new FolderDetailCallback() {
					@Override
					public void onLoaded(FolderInfo folderInfo) {
						if (folderInfo != null)
							detailView.setText(folderInfo.getDetail(mContext));
					}
				});
			}
			
			return true;
		}
		
		public void destroy() {
			mDetailLoader.destroy();
		}
	}

上面的是程序主界面中listview的viewbinder类的定义，可以看到语句mDetailLoader.loadDetailAsy...这条语句，它就相当于View.setonClickListener()一样，只是没有那么直观罢了。

Java代码

public void loadDetailAsync(long folderID, FolderDetailCallback loadedCallback) {
final long folderIDFinal = folderID;
final FolderDetailCallback loadedCallbackFinal = loadedCallback;
mLoaderService.execute(new Runnable() {
@Override
public void run() {
try {
final FolderInfo folderInfo = mDatabase.getFolderInfoFull(folderIDFinal);
mGuiHandler.post(new Runnable() {
@Override
public void run() {
loadedCallbackFinal.onLoaded(folderInfo);
}
});
} catch (Exception e) {
// this is some unimportant background stuff, do not fail
Log.e(TAG, "Error occured while loading full folder info.", e);
}
}
});

	public void loadDetailAsync(long folderID, FolderDetailCallback loadedCallback) {
		final long folderIDFinal = folderID;
		final FolderDetailCallback loadedCallbackFinal = loadedCallback;
		mLoaderService.execute(new Runnable() {
			@Override
			public void run() {
				try {
				final FolderInfo folderInfo = mDatabase.getFolderInfoFull(folderIDFinal);
				
				mGuiHandler.post(new Runnable() {
					@Override
					public void run() {
						loadedCallbackFinal.onLoaded(folderInfo);
					}
				});
				} catch (Exception e) {
					// this is some unimportant background stuff, do not fail
					Log.e(TAG, "Error occured while loading full folder info.", e);
				}
			}
		});

上面是一个实现类似Handler的方法，不过它用了ExecutorService,可以看见参数是FolderDetailCallBack接口，而方法的实现则是调用了接口中定义的空方法，该空方法就是我们在setOnClickListener中实现的onCLick方法。可能上面的描述不是很清楚，我这里写了一个简单的例子

先定义一个接口：

Java代码

public interface MyInterface {
void call(int i);
}

public interface MyInterface {

	void call(int i);
}

再定义一个实现该接口空方法的类A：

Java代码

public class A {
public A() {
}
public void make(MyInterface myInterface) {
int i = 2;
System.out.println("接口回调前的i:" + i);
myInterface.call(i); //调用回调方法
}
}

public class A {
	
	public A() {
		
	}
	public void make(MyInterface myInterface) {
		int i = 2;
		System.out.println("接口回调前的i:" + i);
		myInterface.call(i); //调用回调方法
	}
}

最后是一个测试类：

Java代码

public class B {
public static void main(String[] args){
A a = new A();
a.make(new MyInterface() {
@Override
public void call(int i) {
i = i + 1;
System.out.println("接口回调后的i:" + i);
}
});
}
}

public class B {

	public static void main(String[] args){
		A a = new A();
		a.make(new MyInterface() {
			
			@Override
			public void call(int i) {
				i = i + 1;
				System.out.println("接口回调后的i:" + i);
			}
		});
	}
}

输出：

接口回调前的i:2
接口回调后的i:3

好了，，写的不好>.<，努力努力！以后会慢慢好的。