java - 使用线程时 ImageView 不显示图像

Question

我使用此代码来显示图像，因为我在没有线程的情况下运行它它工作正常，但使用线程我只是获得 ImageView ，其中没有任何图片。对我来说，在程序的这一部分使用线程很重要，因为它非常慢:(这是我的代码:

        @Override
        public View getView(final int position,  View convertView, ViewGroup parent) {
            Log.e("sara" , "this part takes time");


            LayoutInflater inflater = getLayoutInflater();

            convertView = getLayoutInflater().inflate(R.layout.gallery_gridsq, parent, false);
            iv = (ImageView) convertView.findViewById(R.id.icon);
          final File file = new File(Uri.parse(getItem(position).toString()).getPath());
            //File file = new File("/text.jpg");

            Runnable runnable = new Runnable() {
                @Override
                public void run() {

                    Bitmap bmp = null;
                    BitmapFactory.Options options = new BitmapFactory.Options();
            options.inJustDecodeBounds = true;
            try {
                BitmapFactory.decodeStream(new FileInputStream(file), null, options);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }

            options.inJustDecodeBounds = false;
            options.inSampleSize = 2;
            try {
                bmp = BitmapFactory.decodeStream(new FileInputStream(file), null, options);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }

        iv.setImageBitmap(bmp);

                }
            };
            new Thread(runnable).start();
            return convertView;
        }
    }

Answer 1

使用AsyncTask。

文档:https://developer.android.com/reference/android/os/AsyncTask.html

AsyncTask enables proper and easy use of the UI thread. This class allows you to perform background operations and publish results on the UI thread without having to manipulate threads and/or handlers.

在doInBackground()中执行繁重的操作，并在onPostExecute()中将图像设置为imageView。