Question

我在doInBackground()的{{1}}方法中获取了图片的缩略图。如果我使用AsyncTask取消AsyncTask，则运行AsyncTask时会遇到问题。我在logcat中遇到一个奇怪的异常。该应用程序未终止，但logcat显示异常消息。

我的doInBackground（）如下所示

cancel()

getImageThumbnail方法

protected Bitmap doInBackground(String... params) {
        Bitmap bitmap = null;
        String path = params[0];
        bitmap = getImageThumbnail(MainActivity.this,path);
        //Some cache mechanism
        return bitmap;
    }

如果异步任务处于runnign状态，如果我调用public static Bitmap getImageThumbnail(Context context,String path) { ContentResolver cr = context.getContentResolver(); Cursor ca = cr.query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, new String[]{MediaStore.MediaColumns._ID}, MediaStore.MediaColumns.DATA + "=?", new String[]{path}, null); if (ca != null && ca.moveToFirst()) { int id = ca.getInt(ca.getColumnIndex(MediaStore.MediaColumns._ID)); ca.close(); //At this line I am getting exception Bitmap thumbnail = MediaStore.Images.Thumbnails.getThumbnail(cr, id, MediaStore.Images.Thumbnails.MICRO_KIND, null); return thumbnail; } return ((BitmapDrawable) context.getResources().getDrawable(R.drawable.dummy)).getBitmap(); }我在logcat中收到以下消息

asyncTask.cancel(true)

如何避免该异常??

Answer 1

在创建位图缩略图之前，您正在关闭光标，将getImageThumbnail方法更改为如下所示：

public static Bitmap getImageThumbnail(Context context,String path) {
            ContentResolver cr = context.getContentResolver();
            Cursor ca = null;
            ca = cr.query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, new String[]{MediaStore.MediaColumns._ID}, MediaStore.MediaColumns.DATA + "=?", new String[]{path}, null);
            if (ca != null && ca.moveToFirst()) {
                int id = ca.getInt(ca.getColumnIndex(MediaStore.MediaColumns._ID));

                //At this line I am getting exception
                Bitmap thumbnail = MediaStore.Images.Thumbnails.getThumbnail(cr, id, MediaStore.Images.Thumbnails.MICRO_KIND, null);
                ca.close();
                return thumbnail;
            }
            return ((BitmapDrawable) context.getResources().getDrawable(R.drawable.dummy)).getBitmap();
        }

Answer 2

使用asyncTask.cancel(false)取消异步任务。然后，在isCancelled()中致电getImageThumbnail()之前，请先检查doInBackground()。

您的doInBackground()现在将成为：

protected Bitmap doInBackground(String... params) {
    Bitmap bitmap = null;
    String path = params[0];
    if(!isCancelled()) {
        bitmap = getImageThumbnail(MainActivity.this,path);
        //Some cache mechanism
    }
    return bitmap;
}

在isCancelled()中执行任何操作之前，您还应该先检查postExecute()。

在AsyncTask中获取图像缩略图的例外情况

2 个答案: