android - 尝试在android中使用异步从url下载文件时处理异常

Question

我正在使用 AsyncTask 从 Android 中的 URL 下载文件。这是在后台下载文件的类:

//-----------------------------ASYNC DOWNLOADER--------------------------------
    /**
     * Background Async Task to download file
     * */
    class DownloadFileFromURL extends AsyncTask<String, String, String> {

        /**
         * Before starting background thread
         * Show Progress Bar Dialog
         * */
        @SuppressWarnings("deprecation")
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            showDialog(progress_bar_type);
        }

        //TODO Zustzinfos für alle Methoden hinzufügen
        /**
         * This method is called for executing the background task in the AsyncTask.
         * For this tutorial we are only sleeping the thread for the number of 
         * seconds passed as parameter of the function.
         * 
         * @param numSeconds: life of the task
         * @return the result of the background task
         */
        @Override
        protected String doInBackground(String... f_url) {
            int count;
            try {
                URL url = new URL(f_url[0]);
                URLConnection conection = url.openConnection();
                conection.connect();
                // getting file length
                int lenghtOfFile = conection.getContentLength();     
                // input stream to read file - with 8k buffer
                InputStream input = new BufferedInputStream(url.openStream(), 8192);     
                // Output stream to write file
                OutputStream output = new FileOutputStream("/sdcard/"+Name+".xml");

                byte data[] = new byte[1024];    
                long total = 0;  
                while ((count = input.read(data)) != -1) {
                    total += count;
                    // publishing the progress....
                    // After this onProgressUpdate will be called
                    publishProgress(""+(int)((total*100)/lenghtOfFile));

                    // writing data to file
                    output.write(data, 0, count);
                }
                // flushing output
                output.flush();  
                // closing streams
                output.close();
                input.close();

            } catch (Exception e) {
                Log.e("ASYNC",e.getMessage());
            }
            return null;
        }    
        /**
         * Updating progress bar
         * */
        protected void onProgressUpdate(String... progress) {
            // setting progress percentage
            pDialog.setProgress(Integer.parseInt(progress[0]));
       }     
        /**
        * After completing background task
        * Dismiss the progress dialog
        * **/
        @SuppressWarnings("deprecation")
        @Override
        protected void onPostExecute(String error) {
            // dismiss the dialog after the file was downloaded
            dismissDialog(progress_bar_type);
            String xmlPath = Environment.getExternalStorageDirectory().toString() + "/"+Name+".xml";
            Log.d("XMLDOWNLOADPATH", xmlPath);
            Log.d("DOWNLOADXML","End Download XML file");
        }

    }

我希望能够在我的主要 Activity 中识别(异步类是主要 Activity 的内部类)是否存在异常并在对话框或 toast 中显示错误消息。

我尝试将值从 doInBackground() 返回到 onPostExecute() 并将此字符串写入全局字符串变量，如下所示:

protected String doInBackground(String... f_url) {
String error = null;
try {
}
catch(Exception e){
error = e.toString();
}
return error;

@Override
protected void onPostExecute(String error) {
globalStringvariable = error;
}

但这不能正常工作，对话框并不总是显示异常消息。这是解决我的问题的最佳方法吗？

Answer 1

e.getMessage();

这就是您要找的。另请注意，如果您得到 null，可能是因为您将 Exception 作为通用捕获，您应该始终 try catch 特定的 Exception为了取回消息。