AsyncTask 未调用 onProgressUpdate、onPostExecute

Question

我试图了解 AsyncTask 在 Android 上的使用，为此我开发了这个简单的代码。

令人惊讶的是，doInbackground 被正确调用了，我看到了日志，但没有调用其他两种方法。

我错过了什么吗？

  public class DownloadFilesTask extends AsyncTask<Void, Void, Void> {

        protected Void doInBackground(Void... params) {
            try {
                Log.i("Thread","1");
                Thread.sleep(1000);
                Log.i("Thread","2");
                Thread.sleep(1000);
                Log.i("Thread","3");
                Thread.sleep(1000);
                Log.i("Thread","4");
                Thread.sleep(1000);
                Log.i("Thread","5");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return null;
        }

        protected void onProgressUpdate(Void... progress) {
            Log.i("Thread","onProgress");
        }

        protected void onPostExecute(Void... result) {
            Log.i("Thread","onPosts");
        }
    }

[编辑]

除了onProgressUpdate之外，这段代码一切正常

public class DownloadFilesTask extends AsyncTask<Void, Integer, String> {

public String doInBackground(Void... params) {
    try {
        int i = 0;
        Log.i("Thread","1");
        Thread.sleep(1000);
        publishProgress(i++);
        Log.i("Thread","2");
        Thread.sleep(1000);
        publishProgress(i++);
        Log.i("Thread","3");
        Thread.sleep(1000);
        Log.i("Thread","4");
        Thread.sleep(1000);
        Log.i("Thread","5");
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    return "done";
}

public void onProgressUpdate(int progress) {
    Log.i("Thread","onProgress " + progress);
}

public void onPostExecute(String result) {
    Log.i("Thread","onPosts " + result);
}

在这里你可以看到我的 LogCat 的截图：

Answer 1

方法签名错误。它应该看起来像：

protected void onPostExecute(Void result) {
    Log.i("Thread","onPosts");
}

另外，我建议您使用@Override 注释。这样，如果您尝试覆盖错误的方法，您将收到编译时错误。

编辑： 您发布的 onProgressUpdate 的签名是错误的。应该是：

protected void onProgressUpdate(Integer... progress){}

Answer 2

AsyncTask 具有 onProgressUpdate(Void...) 方法，例如，您可以调用每次迭代或每次在 doInBackground() 期间通过调用 publishProgress() 完成进度时。

更多详情请参考docs

所以它应该看起来像这样：

public class DownloadFilesTask extends AsyncTask<Void, Integer, String> {

    protected String doInBackground(Void... params) {
        try {
            int i = 0;
            Log.i("Thread","1");
            Thread.sleep(1000);
            publishProgress(i++);
            Log.i("Thread","2");
            Thread.sleep(1000);
            publishProgress(i++);
            Log.i("Thread","3");
            Thread.sleep(1000);
            Log.i("Thread","4");
            Thread.sleep(1000);
            Log.i("Thread","5");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "done";
    }

    protected void onProgressUpdate(int progress) {
        Log.i("Thread","onProgress " + progress);
    }

    private void onPostExecute(String result) {
        Log.i("Thread","onPosts " + result);
    }
}