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[英]AsyncTask throwing Error “Caused by java.lang.ClassCastException: java.lang.Object[] cannot be cast to java.lang.Void[]” on doinbackground()
[英]Object[] cannot be cast to Void[] in AsyncTask
我在扩展asynctask中遇到此错误,但我确实确定Object []是Void []。
这是我自定义的AsyncTask:
public abstract class RepeatableAsyncTask<A, B, C> extends AsyncTask<A, B, C> {
private static final String TAG = "RepeatableAsyncTask";
public static final int DEFAULT_MAX_RETRY = 5;
private int mMaxRetries = DEFAULT_MAX_RETRY;
private Exception mException = null;
/**
* Default constructor
*/
public RepeatableAsyncTask() {
super();
}
/**
* Constructs an AsyncTask that will repeate itself for max Retries
* @param retries Max Retries.
*/
public RepeatableAsyncTask(int retries) {
super();
mMaxRetries = retries;
}
/**
* Will be repeated for max retries while the result is null or an exception is thrown.
* @param inputs Same as AsyncTask's
* @return Same as AsyncTask's
*/
protected abstract C repeatInBackground(A...inputs);
@Override
protected final C doInBackground(A...inputs) {
int tries = 0;
C result = null;
/* This is the main loop, repeatInBackground will be repeated until result will not be null */
while(tries++ < mMaxRetries && result == null) {
try {
result = repeatInBackground(inputs);
} catch (Exception exception) {
/* You might want to log the exception everytime, do it here. */
mException = exception;
}
}
return result;
}
/**
* Like onPostExecute but will return an eventual Exception
* @param c Result same as AsyncTask
* @param exception Exception thrown in the loop, even if the result is not null.
*/
protected abstract void onPostExecute(C c, Exception exception);
@Override
protected final void onPostExecute(C c) {
super.onPostExecute(c);
onPostExecute(c, mException);
}
这是产生问题的子类:
public class ListPalinasAsynkTask extends RepeatableAsyncTask<Void, Void, List<Palina>>{
private static final String TAG = "ListPalinasAsynkTask";
private static final boolean D = SystemConstants.ACTIVE_DEBUG;
private ApiRequest.ListPalinasCallback mCallback;
public ListPalinasAsynkTask(ApiRequest.ListPalinasCallback callback) {
if(D) Log.d(TAG, "Called: ListPalinasAsynkTask([callback])");
mCallback = callback;
}
@Override
protected List<Palina> repeatInBackground(Void... voids) {
/* Here i send request to get palinas */
return Api.getPalinasNearMe();
}
@Override
protected void onPostExecute(List<Palina> palinas, Exception exception) {
if(exception != null)
Logging.e(TAG, "Received exception in Asynk Task", exception);
if(palinas != null)
mCallback.result(palinas);
else
mCallback.result(new ArrayList<Palina>());
}
}
最后,这是错误:
E/ListPalinasAsynkTask﹕ Received exception in Asynk Task
java.lang.ClassCastException: java.lang.Object[] cannot be cast to java.lang.Void[]
at ListPalinasAsynkTask.repeatInBackground(ListPalinasAsynkTask.java:19)
at RepeatableAsyncTask.doInBackground(RepeatableAsyncTask.java:43)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
我无法解释此异常,因为我将Void作为参数! 那不应该是一个对象。 你有解决方案吗?
编辑 :ListPalinasAsyncTask.java:19是指:
public class ListPalinasAsynkTask extends RepeatableAsyncTask<Void, Void, List<Palina>> {
RepeatableAsyncTask.java:43:
result = repeatInBackground(inputs);
编辑2:
我这样调用执行:
AsyncTask mAsyncTask = new ListPalinasAsynkTask(callback);
....
mAsyncTask.execute();
找到解决方案:
问题是这样的:
AsyncTask mAsyncTask = new ListPalinasAsynkTask(callback);
....
mAsyncTask.execute();
我正在使用通用的AsyncTask调用execute,该类将通过Void作为参数,并且永远不会在ListPalinasAsynkTask上调用.execute(),而是将调用ListPalinasAsynkTask.execute(Void)。 那给出了错误。
解决方案:
像这样:
public abstract class VoidRepeatableAsyncTask<T> extends RepeatableAsyncTask<Void, Void, T> {
public void execute() {
super.execute();
}
}
然后,您可以轻松地使用如下代码来调用execute:
VoidRepeatableAsyncTask mAsyncTask = new ListPalinasAsynkTask(callback);
....
mAsyncTask.execute();
这将调用AsyncTask的无参数execute方法。
我解决此问题的另一种方法是即使在不使用参数的情况下,也可以在参数中传递Object
。
new AsyncTask<Object, Void, MergeAdapter>()
和覆盖:
@Override
protected ReturnClass doInBackground(Object... params) {
//...
}
如果您想将不同类型的AsyncTasks传递给方法,则上述情况适用(以我为例),当然您并不关心参数。
我认为解决方案要简单得多。 只需以这种方式创建子类对象:
AsyncTask<Void, Void, List<Palina> mAsyncTask = new ListPalinasAsynkTask(callback);
....
mAsyncTask.execute();
尝试使用:
result = repeatInBackground((Void) inputs);
代替
result = repeatInBackground(inputs);
如果发生此问题,则您可能已经创建了派生类对象并添加了其基类变量(AsyncTask)。 因此发生此错误。
AsyncTask mAsyncTask = new ListPalinasAsynkTask(callback);
当您喜欢这样的“执行未检查的调用。参数...”时,棉绒也会发出警告。
解决方案是ListPalinasAsynkTask mAsyncTask = new ListPalinasAsynkTask(callback); 然后调用执行。 会很好的
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