Question

private class DownloadLargeFileTask extends AsyncTask<Void, Void, Void> 
{
    private final ProgressDialog dialog;

    public DownloadLargeFileTask(ProgressDialog dialog) {
         this.dialog = dialog;
    }

    protected void onPreExecute() {
        dialog.show();
    }


    protected void onPostExecute(Void unused) {
        dialog.dismiss();
    }

    @Override
    protected Void doInBackground(Void... arg0) {
        download();
        return null;
    }
}

private void download ()
{
    try 
    {
        long startTime = System.currentTimeMillis();

        URL u = new URL("http://mds.podfm.ru/188/download/040_Sergejj_Palijj_-_Karantin_CHast_2.mp3");
        HttpURLConnection c = (HttpURLConnection) u.openConnection();

        c.setRequestMethod("GET");
        c.setDoOutput(true);
        c.connect();
        FileOutputStream f = new FileOutputStream(new File("/sdcard/","my.mp3"));

        InputStream in = c.getInputStream();

        byte[] buffer = new byte[1024];
        int len1 = 0;
        int downloadedSize = 0;
        while ( (len1 = in.read(buffer)) != -1 ) 
        {
          f.write(buffer,0, len1);
          downloadedSize += len1; 
          ReturnDownloadedBytes(downloadedSize);
        }
        f.close();
        Log.d("ImageManager", "download ready in" + ((System.currentTimeMillis() - startTime) / 1000) + " sec");
    }
    catch (IOException e)
    {
        Log.d("ImageManager", "Error" + ((System.currentTimeMillis()) / 1000) + e + " sec");
    }
}

private void ReturnDownloadedBytes(int size)
{
    text.setText(String.valueOf(size));

}

错误说：只有创建视图层次结构的原始线程才能触及其视图。我认为这意味着我从一个therad创建textview并尝试从另一个（AsyncTask）访问但是如何获得它？感谢

修改
这是所有代码。但是，即使我发送publishProgress(downloadedSize) int value = 10，它也会以text.setText(String.valueOf(progress));不同的值来监听输出，例如[Ljava.lang.float;@43ed62f78

public class list extends Activity {

private TextView text;



@Override
public void onCreate(Bundle icicle)
{
    super.onCreate(icicle);
    setContentView(R.layout.main);

    text = (TextView)findViewById(R.id.result);
}

public void selfDestruct(View view) {

    ProgressDialog dialog = new ProgressDialog(this);
    dialog.setMessage("????????. ?????...");
    new DownloadLargeFileTask(dialog).execute();

}


private class DownloadLargeFileTask extends AsyncTask<Void, Integer, Void> 
{
    private final ProgressDialog dialog;

    public DownloadLargeFileTask(ProgressDialog dialog) {
         this.dialog = dialog;
    }

    protected void onPreExecute() {
        dialog.show();
    }


    protected void onPostExecute(Void unused) {
        dialog.dismiss();
    }

    protected void onProgressUpdate(Integer...progress) {

        text.setText(String.valueOf(progress));

    }

    @Override
    protected Void doInBackground(Void... arg0) {
        try 
        {
            long startTime = System.currentTimeMillis();

            URL u = new URL("http://mds.podfm.ru/188/download/040_Sergejj_Palijj_-_Karantin_CHast_2.mp3");
            HttpURLConnection c = (HttpURLConnection) u.openConnection();

            c.setRequestMethod("GET");
            c.setDoOutput(true);
            c.connect();
            FileOutputStream f = new FileOutputStream(new File("/sdcard/","my.mp3"));

            InputStream in = c.getInputStream();

            byte[] buffer = new byte[1024];
            int len1 = 0;
            int downloadedSize = 10;
            while ( (len1 = in.read(buffer)) != -1 ) 
            {
              f.write(buffer,0, len1);
              //downloadedSize += len1; 
              **publishProgress(downloadedSize);**
            }
            f.close();
            Log.d("ImageManager", "download ready in" + ((System.currentTimeMillis() - startTime) / 1000) + " sec");
        }
        catch (IOException e)
        {
            Log.d("ImageManager", "Error" + ((System.currentTimeMillis()) / 1000) + e + " sec");
        }
        return null;
    }
}

Answer 1

您可以通过将进度发布到UI线程来更改UI。从doInBackground调用publishProgress。这将在AsyncTask中调用onProgressUpdate，您可以在其中更新UI。

您必须在AsyncTask中定义onProgressUpdate。 http://developer.android.com/reference/android/os/AsyncTask.html#onProgressUpdate(Progress ...）

Answer 2

您对错误的评估是正确的。我假设text是TextView中定义的Activity对象，因此它是在UI线程中创建的。在doInBackground()内运行的代码在单独的线程中运行。只有UI线程可以对UI元素执行更新，因此当您尝试调用setText时，您会收到您报告的错误消息。

Abhinav在如何解决问题方面也是正确的，因为AsyncTask有一个方法可以调用以从后台线程向UI线程发送更新：publishProgress，它调用{{1} }}

将此方法添加到onProgressUpdate()：

AsyncTask

并更改@Override protected void onProgressUpdate(Integer... integer){ text.setText(integer[0].toString()); }中的while循环：

download()

试图下载文件大小，但收到错误

2 个答案: