Question

我正在创建一个正在下载文件的应用，然后将其加载到imageview但我收到此错误

    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageBitmap(android.graphics.Bitmap)' on a null object reference

这是我的下载代码

   class DownloadFileFromURL extends AsyncTask<String, String, String> {


        // Show Progress bar before downloading Music
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Shows Progress Bar Dialog and then call doInBackground method
            showDialog(progress_bar_type);
        }

        // Download File from Internet
        @Override
        protected String doInBackground(String... f_url) {
            int count;
            try {
                URL url = new URL(f_url[0]);
                URLConnection conection = url.openConnection();
                conection.connect();
                // Get Music file length
                int lenghtOfFile = conection.getContentLength();
                // input stream to read file - with 8k buffer
                InputStream input = new BufferedInputStream(url.openStream(),10*1024);
                // Output stream to write file in SD card
                int imageNr = sharedPreferences.getInt("ImageNr", 1);
                OutputStream output = new FileOutputStream(getApplicationInfo().dataDir+"/files/"+imageNr+".jpg");

                byte data[] = new byte[1024];
                long total = 0;
                while ((count = input.read(data)) != -1) {
                    output.write(data, 0, count);
                    total += count;
                    // Publish the progress which triggers onProgressUpdate method
                    publishProgress("" + (total));

                    // Write data to file

                }
                // Flush output
                output.flush();
                // Close streams
                output.close();
                input.close();
            } catch (Exception e) {
                Log.e("Error: ", e.getMessage());
            }
            return null;
        }
        // While Downloading Music File
        protected void onProgressUpdate(String... progress) {
            // Set progress percentage
            prgDialog.setProgress(Integer.parseInt(progress[0]));
        }

        // Once File is downloaded
        @Override
        protected void onPostExecute(String file_url) {
            // Dismiss the dialog after the Music file was downloaded
            dismissDialog(progress_bar_type);

            int imageNr = sharedPreferences.getInt("ImageNr", 1);
            File imgFile = new File(getApplicationInfo().dataDir+"/files/"+imageNr+".jpg");
            imageNr++;
            SharedPreferences.Editor editorsave = sharedPreferences.edit();
            editorsave.putInt("ImageNr", imageNr);
            editorsave.apply();

            if(imgFile.exists()){
                Toast.makeText(getApplicationContext(), "Bild laddad!", Toast.LENGTH_LONG).show();

                Bitmap myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());

                imageView.setImageBitmap(myBitmap);

            }else{
                Toast.makeText(getApplicationContext(), "Bild ej hittad!", Toast.LENGTH_LONG).show();
            }
            // Do stuff here

        }
    }

是的，它使用了一些弃用的代码，但这在我的其他应用程序中对我有用，虽然我没有在那个中使用位图，但是AsyncTask有效。

Answer 1

您的imageView为空

远离异常本身

if(imgFile.exists() && imageView != null) {
....

检查您的imageView参考分配。似乎没有正确分配imageView引用，因此返回null

imageview

1 个答案: