捕获AsyncTask的异常.需要思考

Question

我想捕获doInBackground中的线程异常并在onPostExcecute中打印错误消息.问题是我在onPostExecute中没有Throwable对象.如何捕获异常在非UI线程,并打印在UI线程的错误信息？

public class TestTask extends AsyncTask<Void, Void, List<String>> {

    @Override
    protected List<String> doInBackground(final Void... params) {
        try {
            ...
            return listOfString;
        } catch(SomeCustomException e) {
            ...
            return null;
        }       
    }

    @Override
    protected void onPostExecute(final List<String> result) {
        if(result == null) {
            // print the error of the Throwable "e".
            // The problem is I don't have the Throwable object here! So I can't check the type of exception.
        }

    }
}

Arun回答后更新:

这是我的AsyncTask包装类.它打算在doInBackground中处理Exception,但我找不到一个好的解决方案来做到这一点.

public abstract class AbstractWorkerTask<Params, Progress, Result>
extends AsyncTask<Params, Progress, Result>
implements Workable {
    protected OnPreExecuteListener onPreExecuteListener;
    protected OnPostExecuteListener<Result> onPostExecuteListener;
    protected ExceptionHappenedListener exceptionHappendedListener;
    private boolean working;

    @Override
    protected void onPreExecute() {
        if (onPreExecuteListener != null) {
            onPreExecuteListener.onPreExecute();
        }
        working = true;
    }

    @Override
    protected void onPostExecute(final Result result) {
        working = false;
        if(/* .........*/ ) {
            exceptionHappendedListener.exceptionHappended(e);
        }
        if (onPostExecuteListener != null) {
            onPostExecuteListener.onPostExecute(result);
        }
    }

    @Override
    public boolean isWorking() {
        return working;
    }

    public void setOnPreExecuteListener(final OnPreExecuteListener onPreExecuteListener) {
        this.onPreExecuteListener = onPreExecuteListener;
    }

    public void setOnPostExecuteListener(final OnPostExecuteListener<Result> onPostExecuteListener) {
        this.onPostExecuteListener = onPostExecuteListener;
    }

    public void setExceptionHappendedListener(final ExceptionHappenedListener exceptionHappendedListener) {
        this.exceptionHappendedListener = exceptionHappendedListener;
    }

    public interface OnPreExecuteListener {
        void onPreExecute();
    }

    public interface OnPostExecuteListener<Result> {
        void onPostExecute(final Result result);
    }

    public interface ExceptionHappenedListener {
        void exceptionHappended(Exception e);
    }
}

Answer 1

更改doInBackground()to 的返回类型Object以及在收到结果时onPostExecute(Object result)使用instanceOf运算符来检查返回的结果是否为a Exception或List<String>.

编辑

由于结果可以是Exception,也可以是正确的List,您可以使用以下命令:

protected void onPostExecute(final Object result) {
    working = false;
    if(result instanceof SomeCustomException) {
        exceptionHappendedListener.exceptionHappended(result);
    }
    else{
        if (onPostExecuteListener != null) {
            onPostExecuteListener.onPostExecute(result);
        }
    }
}

同时更改以下声明:

public abstract class AbstractWorkerTask<Params, Progress, Object> extends AsyncTask<Params, Progress, Object>