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我正在尝试完成我的 DownloadFile 类，它是 AsyncTask 的子类。所以这是类的代码：

private class DownloadFile extends AsyncTask<String, Integer, String>
{
    @Override
    protected String doInBackground(String... sUrl)
    {
        try
        {
            URL url = new URL(sUrl[0]);
            URLConnection urlc = url.openConnection();
            urlc.connect();
            int fileLength = urlc.getContentLength();
            InputStream is = new BufferedInputStream(url.openStream());
            OutputStream os = new FileOutputStream(Environment.getDataDirectory().getAbsolutePath().concat("data/com.markosoft.maturko/databases/proba.mp3"));
            byte Data[] = new byte[1024];
            long total = 0;
            int count;
            while((count=is.read(Data))!=-1)
            {
                total+=count;
                publishProgress((int)total * 100 / fileLength);
                os.write(Data,0,count);
            }
            os.flush();
            os.close();
            is.close();
        }
        catch(Exception e)
        {

        }
        return null;
    }
    @Override
    protected void onProgressUpdate(Integer... progress)
    {
        dl.setProgress(progress[0]);
    }
    @Override
    protected void onPostExecute(String unused)
    {
        dl.dismiss();
        Toast.makeText(getActivity(), "Podaci uspešno preuzeti", Toast.LENGTH_SHORT).show();
    }
}

我收到 NullPointerException 错误和“线程退出未捕获的异常”错误。当我添加显示下载已完成的 Toast 调用时发生此错误，但据我所知 onPostExecute 是在 UI 线程上执行的，所以我没有看到问题。让我烦恼的另一件事是下载没有完成，或者根本没有开始。当我调用调用 DownloadFile.execute(link) 函数的函数时，onPostExecute 函数会立即激活...感谢您的帮助

编辑：dl 是在调用 dlf.execute(link) 之前初始化的 ProgressDialog，因此这不应该是 NullPointerException 的原因...编辑：这是请求的 LogCat 日志：

03-22 19:56:51.119: W/dalvikvm(546): threadid=1: thread exiting with uncaught exception (group=0x409961f8)
03-22 19:56:51.140: E/AndroidRuntime(546): FATAL EXCEPTION: main
03-22 19:56:51.140: E/AndroidRuntime(546): java.lang.NullPointerException
03-22 19:56:51.140: E/AndroidRuntime(546):  at android.widget.Toast.<init>(Toast.java:92)
03-22 19:56:51.140: E/AndroidRuntime(546):  at android.widget.Toast.makeText(Toast.java:233)
03-22 19:56:51.140: E/AndroidRuntime(546):  at com.markosoft.maturko.Upit$DownloadFile.onPostExecute(Upit.java:68)
03-22 19:56:51.140: E/AndroidRuntime(546):  at com.markosoft.maturko.Upit$DownloadFile.onPostExecute(Upit.java:1)
03-22 19:56:51.140: E/AndroidRuntime(546):  at android.os.AsyncTask.finish(AsyncTask.java:602)
03-22 19:56:51.140: E/AndroidRuntime(546):  at android.os.AsyncTask.access$600(AsyncTask.java:156)
03-22 19:56:51.140: E/AndroidRuntime(546):  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:615)
03-22 19:56:51.140: E/AndroidRuntime(546):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-22 19:56:51.140: E/AndroidRuntime(546):  at android.os.Looper.loop(Looper.java:137)
03-22 19:56:51.140: E/AndroidRuntime(546):  at android.app.ActivityThread.main(ActivityThread.java:4340)
03-22 19:56:51.140: E/AndroidRuntime(546):  at java.lang.reflect.Method.invokeNative(Native Method)
03-22 19:56:51.140: E/AndroidRuntime(546):  at java.lang.reflect.Method.invoke(Method.java:511)
03-22 19:56:51.140: E/AndroidRuntime(546):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-22 19:56:51.140: E/AndroidRuntime(546):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-22 19:56:51.140: E/AndroidRuntime(546):  at dalvik.system.NativeStart.main(Native Method)

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4

2 回答 2

3

http://developer.android.com/reference/android/os/AsyncTask.html. Look at the topic under heading The 4 steps.

You are getting NullPointerException for the Toast. If you calling asynctask from say MainActivity then

Try

  Toast.makeText(MainActivity.this, "Podaci uspešno preuzeti", Toast.LENGTH_SHORT).show();

Your should pass activity context,your text and duration as parameters to makeText.

                                   OR

As suggested by Eng.Fouad your dl is null.

于 2013-03-22T18:52:56.543 回答
1

我怀疑这是因为dlis null，所以在第一次调用时onProgressUpdate()， aNullPointerException被 in 中的 catch-bock 抛出并捕获doInBackground()。

接下来，onPostExecute()被调用并NullPointerException再次抛出，但这一次它被传播到应用程序的 android 主启动器。

于 2013-03-22T18:47:23.643 回答