对Android中的AsyncTask进行函数化的封装，简洁调用
为了使UI在数据获取时不僵死，数据获取需要在新开Worker线程中进行，然后将返回结果在UI线程中进行读取并渲染页面。面对这种异步处理，到底如何写才简洁，先后面临过三种实现方式。
首先是最原始的Java方式，new 一个Thread出来，将处理Runnable进去执行，执行完之后通过handler post到ui线程去更新界面。然后发现1.5后有了AsyncTask，非常好用，以后的项目中全部改成衍生出一个AsyncTask的子类，类中自然定义了运行前方法、运行中方法和运行后在ui中运行的方法。目前我做的项目中对AsyncTask做了封装，把它从原本的子类编写的过程，改成了函数调用方式，这就是目前正使用的第三种方法。
一个Android应用中，Activity通常可以建立以上层次关系。然后，在BaseActivity中对AsyncTask进行了封装，形成doAsync方法。方法体内创建一个新的AsyncTask并执行，由于AsyncTask是泛型参数，doAsync方法中传入的接口的参数也对应使用了泛型。至此，一个典型的异步调用的案例如下：
this.doAsync(new Callable() {
// 希望异步加载的数据
public String call() throws Exception {
String resu = NetworkTool.httpGetURL(
"http://www.baidu.com", "GBK");
return resu;
}
}, new Callback() {
// 当加载完成后回调，在UI线程中的操作
public void onCallback(final String resu) {
if (null != resu) {
tv_text1.setText(getRT().text1 + resu);
} else {
Tools.ShowNetErr(HomeActivity.this);
}
}
});
这样，就从本来继承AsyncTask创建一个子类，然后初始化，然后运行的开发过程转变为了函数调用的过程。可以看到，调用可是简洁了很多!
为了实现它，我们附上BaseActivity中如下封装代码，需要说明的是这不是我的原创，我借鉴于Andengine引擎的实现代码进行的修改。
附源码：
public class ActivityUtils {
public static void doAsync(final Context pContext, final int pTitleResID, final int pMessageResID, final Callable pCallable, final Callback pCallback) {
ActivityUtils.doAsync(pContext, pTitleResID, pMessageResID, pCallable, pCallback, null, false);
}
public static void doAsync(final Context pContext, final CharSequence pTitle, final CharSequence pMessage, final Callable pCallable, final Callback pCallback) {
ActivityUtils.doAsync(pContext, pTitle, pMessage, pCallable, pCallback, null, false);
}
public static void doAsync(final Context pContext, final int pTitleResID, final int pMessageResID, final Callable pCallable, final Callback pCallback, final boolean pCancelable) {
ActivityUtils.doAsync(pContext, pTitleResID, pMessageResID, pCallable, pCallback, null, pCancelable);
}
public static void doAsync(final Context pContext, final CharSequence pTitle, final CharSequence pMessage, final Callable pCallable, final Callback pCallback, final boolean pCancelable) {
ActivityUtils.doAsync(pContext, pTitle, pMessage, pCallable, pCallback, null, pCancelable);
}
public static void doAsync(final Context pContext, final int pTitleResID, final int pMessageResID, final Callable pCallable, final Callback pCallback, final Callback pExceptionCallback) {
ActivityUtils.doAsync(pContext, pTitleResID, pMessageResID, pCallable, pCallback, pExceptionCallback, false);
}
public static void doAsync(final Context pContext, final CharSequence pTitle, final CharSequence pMessage, final Callable pCallable, final Callback pCallback, final Callback pExceptionCallback) {
ActivityUtils.doAsync(pContext, pTitle, pMessage, pCallable, pCallback, pExceptionCallback, false);
}
public static void doAsync(final Context pContext, final int pTitleResID, final int pMessageResID, final Callable pCallable, final Callback pCallback, final Callback pExceptionCallback, final boolean pCancelable) {
ActivityUtils.doAsync(pContext, pContext.getString(pTitleResID), pContext.getString(pMessageResID), pCallable, pCallback, pExceptionCallback, pCancelable);
}
public static void doAsync(final Context pContext, final CharSequence pTitle, final CharSequence pMessage, final Callable pCallable, final Callback pCallback, final Callback pExceptionCallback, final boolean pCancelable) {
new AsyncTask() {
private ProgressDialog mPD;
private Exception mException = null;
@Override
public void onPreExecute() {
this.mPD = ProgressDialog.show(pContext, pTitle, pMessage, true, pCancelable);
if(pCancelable) {
this.mPD.setOnCancelListener(new OnCancelListener() {
@Override
public void onCancel(final DialogInterface pDialogInterface) {
pExceptionCallback.onCallback(new CancelledException());
pDialogInterface.dismiss();
}
});
}
super.onPreExecute();
}
@Override
public T doInBackground(final Void... params) {
try {
return pCallable.call();
} catch (final Exception e) {
this.mException = e;
}
return null;
}
@Override
public void onPostExecute(final T result) {
try {
this.mPD.dismiss();
} catch (final Exception e) {
Log.e("Error", e.toString());
}
if(this.isCancelled()) {
this.mException = new CancelledException();
}
if(this.mException == null) {
pCallback.onCallback(result);
} else {
if(pExceptionCallback == null) {
if (this.mException != null)
Log.e("Error", this.mException.toString());
} else {
pExceptionCallback.onCallback(this.mException);
}
}
super.onPostExecute(result);
}
}.execute((Void[]) null);
}
public static void doProgressAsync(final Context pContext, final int pTitleResID, final ProgressCallablepCallable, final Callback pCallback) {
ActivityUtils.doProgressAsync(pContext, pTitleResID, pCallable, pCallback, null);
}
public static void doProgressAsync(final Context pContext, final int pTitleResID, final ProgressCallablepCallable, final Callback pCallback, final Callback pExceptionCallback) {
new AsyncTask() {
private ProgressDialog mPD;
private Exception mException = null;
@Override
public void onPreExecute() {
this.mPD = new ProgressDialog(pContext);
this.mPD.setTitle(pTitleResID);
this.mPD.setIcon(android.R.drawable.ic_menu_save);
this.mPD.setIndeterminate(false);
this.mPD.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
this.mPD.show();
super.onPreExecute();
}
@Override
public T doInBackground(final Void... params) {
try {
return pCallable.call(new IProgressListener() {
@Override
public void onProgressChanged(final int pProgress) {
onProgressUpdate(pProgress);
}
});
} catch (final Exception e) {
this.mException = e;
}
return null;
}
@Override
public void onProgressUpdate(final Integer... values) {
this.mPD.setProgress(values[0]);
}
@Override
public void onPostExecute(final T result) {
try {
this.mPD.dismiss();
} catch (final Exception e) {
Log.e("Error", e.getLocalizedMessage());
/* Nothing. */
}
if(this.isCancelled()) {
this.mException = new CancelledException();
}
if(this.mException == null) {
pCallback.onCallback(result);
} else {
if(pExceptionCallback == null) {
Log.e("Error", this.mException.getLocalizedMessage());
} else {
pExceptionCallback.onCallback(this.mException);
}
}
super.onPostExecute(result);
}
}.execute((Void[]) null);
}
public static void doAsync(final Context pContext, final int pTitleResID, final int pMessageResID, final AsyncCallable pAsyncCallable, final Callback pCallback, final Callback pExceptionCallback) {
final ProgressDialog pd = ProgressDialog.show(pContext, pContext.getString(pTitleResID), pContext.getString(pMessageResID));
pAsyncCallable.call(new Callback() {
@Override
public void onCallback(final T result) {
try {
pd.dismiss();
} catch (final Exception e) {
Log.e("Error", e.getLocalizedMessage());
/* Nothing. */
}
pCallback.onCallback(result);
}
}, pExceptionCallback);
}
public static class CancelledException extends Exception {
private static final long serialVersionUID = -78123211381435595L;
}
}
public interface AsyncCallable {
// ===========================================================
// Final Fields
// ===========================================================
// ===========================================================
// Methods
// ===========================================================
/**
* Computes a result asynchronously, return values and exceptions are to be handled through the callbacks.
* This method is expected to return almost immediately, after starting a {@link Thread} or similar.
*
* @return computed result
* @throws Exception if unable to compute a result
*/
public void call(final Callback pCallback, final Callback pExceptionCallback);
}
public interface Callback {
// ===========================================================
// Final Fields
// ===========================================================
// ===========================================================
// Methods
// ===========================================================
/**
* 当加载完成后回调，加载完毕的事后处理
*/
public void onCallback(final T pCallbackValue);
}
public interface IProgressListener {
// ===========================================================
// Constants
// ===========================================================
// ===========================================================
// Methods
// ===========================================================
/**
* @param pProgress between 0 and 100.
*/
public void onProgressChanged(final int pProgress);
}
public interface IProgressListener {
// ===========================================================
// Constants
// ===========================================================
// ===========================================================
// Methods
// ===========================================================
/**
* @param pProgress between 0 and 100.
*/
public void onProgressChanged(final int pProgress);
}
public class BaseActivity extends Activity {
/**
*
* @param 模板参数，操作时要返回的内容
* @param pCallable 需要异步调用的操作
* @param pCallback 回调
*/
protected void doAsync(final Callable pCallable, final Callback pCallback) {
ActivityUtils.doAsync(this, null, "内容读取中，请稍等...", pCallable, pCallback, null, false);
}
protected void doAsync(final CharSequence pTitle, final CharSequence pMessage, final CallablepCallable, final Callback pCallback) {
ActivityUtils.doAsync(this, pTitle, pMessage, pCallable, pCallback, null, false);
}
/**
* Performs a task in the background, showing a {@link ProgressDialog},
* while the {@link Callable} is being processed.
*
* @param
* @param pTitleResID
* @param pMessageResID
* @param pErrorMessageResID
* @param pCallable
* @param pCallback
*/
protected void doAsync(final int pTitleResID, final int pMessageResID, final Callable pCallable, final Callback pCallback) {
this.doAsync(pTitleResID, pMessageResID, pCallable, pCallback, null);
}
/**
* Performs a task in the background, showing a indeterminate {@link ProgressDialog},
* while the {@link Callable} is being processed.
*
* @param
* @param pTitleResID
* @param pMessageResID
* @param pErrorMessageResID
* @param pCallable
* @param pCallback
* @param pExceptionCallback
*/
protected void doAsync(final int pTitleResID, final int pMessageResID, final Callable pCallable, final Callback pCallback, final Callback pExceptionCallback) {
ActivityUtils.doAsync(this, pTitleResID, pMessageResID, pCallable, pCallback, pExceptionCallback);
}
/**
* Performs a task in the background, showing a {@link ProgressDialog} with an ProgressBar,
* while the {@link AsyncCallable} is being processed.
*
* @param
* @param pTitleResID
* @param pMessageResID
* @param pErrorMessageResID
* @param pAsyncCallable
* @param pCallback
*/
protected void doProgressAsync(final int pTitleResID, final ProgressCallable pCallable, final CallbackpCallback) {
this.doProgressAsync(pTitleResID, pCallable, pCallback, null);
}
/**
* Performs a task in the background, showing a {@link ProgressDialog} with a ProgressBar,
* while the {@link AsyncCallable} is being processed.
*
* @param
* @param pTitleResID
* @param pMessageResID
* @param pErrorMessageResID
* @param pAsyncCallable
* @param pCallback
* @param pExceptionCallback
*/
protected void doProgressAsync(final int pTitleResID, final ProgressCallable pCallable, final CallbackpCallback, final Callback pExceptionCallback) {
ActivityUtils.doProgressAsync(this, pTitleResID, pCallable, pCallback, pExceptionCallback);
}
/**
* Performs a task in the background, showing an indeterminate {@link ProgressDialog},
* while the {@link AsyncCallable} is being processed.
*
* @param
* @param pTitleResID
* @param pMessageResID
* @param pErrorMessageResID
* @param pAsyncCallable
* @param pCallback
* @param pExceptionCallback
*/
protected void doAsync(final int pTitleResID, final int pMessageResID, final AsyncCallable pAsyncCallable, final Callback pCallback, final Callback pExceptionCallback) {
ActivityUtils.doAsync(this, pTitleResID, pMessageResID, pAsyncCallable, pCallback, pExceptionCallback);
}
}