Android打开图像到图库 - 没有缩略图消息

Question

如果我使用以下代码保存图像，然后手动打开我的图库，图像显示正常。如果我尝试以编程方式打开图库，我会从图库中收到一条消息，说“没有缩略图”。

//save bitmap--------------------------------------------------
                File myDir=new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)+"");
                myDir.mkdirs();
                Random generator = new Random();
                int n = 10000;
                n = generator.nextInt(n);
                String fname = "Image-"+ n +".jpg";
                File file = new File (myDir, fname);
                if (file.exists ()) file.delete ();
                try {
                    FileOutputStream out = new FileOutputStream(file);
                    bitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);
                    out.flush();
                    out.close();

                } catch (Exception e) {
                    e.printStackTrace();
                }
                //media scan--------------------------------------------------
                Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
                File f = new File(myDir.getAbsolutePath());
                Uri contentUri = Uri.fromFile(f);
                mediaScanIntent.setData(contentUri);
                this.getApplicationContext().sendBroadcast(mediaScanIntent);

                //view in gallery (here is where my gallery gives "No Thumbnail" message)----
                Intent viewIntent = new Intent();
                viewIntent.setAction(Intent.ACTION_VIEW);
                viewIntent.setDataAndType(Uri.parse(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)+""),"image/*");
                startActivity(viewIntent);