使用asynctask从内容提供商加载图像位图

我一直试图通过MediaStore内容提供商查询SD卡上的所有图像，并在GridView上显示它们的缩略图。使用asynctask从内容提供商加载图像位图

但是，如果我加载主线程上的图像的缩略图，滚动得慢得令人难以置信...

所以我试图加载通过asynctasks位图：滚动性能变得更好，但现在的电网项目保持重装他们的缩略图，直到它得到正确的位图...

这里是我的AsyncTask，它加载位图：

package x.y; 

import java.lang.ref.WeakReference; 

import android.content.ContentResolver; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory.Options; 
import android.os.AsyncTask; 
import android.provider.MediaStore; 
import android.widget.ImageView; 

public class ImageThumbnailLoader extends AsyncTask<Long, Void, Bitmap> { 

    private final Options mOptions; 

    private WeakReference<ImageView> mImageViewWeakReference; 
    private ContentResolver mContentResolver; 

     public ImageThumbnailLoader(ImageView imageView, 
       ContentResolver cr) { 
     mContentResolver = cr; 
     mImageViewWeakReference = new WeakReference<ImageView>(imageView); 
     mOptions = new Options(); 
     mOptions.inSampleSize = 4; 
    } 



    @Override 
    protected Bitmap doInBackground(Long... params) { 
     Bitmap result; 
      result = MediaStore.Images.Thumbnails.getThumbnail(
        mContentResolver, params[0], 
        MediaStore.Images.Thumbnails.MINI_KIND, mOptions); 
     return result; 
    } 

    @Override 
    protected void onPostExecute(Bitmap result) { 
     super.onPostExecute(result); 
      if (mImageViewWeakReference != null 
        && mImageViewWeakReference.get() != null) 
       mImageViewWeakReference.get().setImageBitmap(result); 
    } 

}

这里是我的自定义光标适配器：

package x.y; 

import android.content.Context; 
import android.database.Cursor; 
import android.graphics.BitmapFactory.Options; 
import android.provider.MediaStore; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.CursorAdapter; 
import android.widget.ImageView; 

public class MediaCursorAdapter extends CursorAdapter { 

    private LayoutInflater mInflater; 
    private final static int mColumnID = 0; 
    private Options mOptions; 

    public MediaCursorAdapter(Context context, Cursor c) { 
     super(context, c); 

     mInflater = LayoutInflater.from(context); 
     mOptions = new Options(); 
     mOptions.inSampleSize = 4; 
    } 

    @Override 
    public void bindView(View view, Context context, Cursor cursor) { 

     ViewHolder holder = (ViewHolder) view.getTag(); 
     ImageThumbnailLoader imageLoader = new ImageThumbnailLoader(holder.thumbImg, 
       context.getContentResolver()); 
     imageLoader.execute(cursor.getLong(mColumnID)); 
//  holder.thumbImg.setImageBitmap(MediaStore.Images.Thumbnails.getThumbnail(
//     context.getContentResolver(), cursor.getLong(mColumnID), 
//     MediaStore.Images.Thumbnails.MINI_KIND, mOptions)); 
     Log.i("Prototype", "bindView : " + cursor.getPosition()); 
    } 

    @Override 
    public View newView(Context context, Cursor cursor, ViewGroup parent) { 
     Log.i("Prototype", "newView : " + cursor.getPosition()); 
     View view = mInflater.inflate(R.layout.grid_item, null); 
     ViewHolder holder = new ViewHolder(view); 
     view.setTag(holder); 
     return view; 
    } 


    private static class ViewHolder { 
     ImageView thumbImg, dragImg; 

     ViewHolder(View base) { 
      thumbImg = (ImageView) base.findViewById(R.id.thumbImage); 
      dragImg = (ImageView) base.findViewById(R.id.dragImage); 
     } 
    } 

}

我查询光标与此代码，并将其发送到适配器：

query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, new String[] { MediaStore.Images.Media._ID, 
      MediaStore.Images.Media.DATA }, null, null, 
    MediaStore.Images.Media._ID);

貌似在我的定义光标适配器bindview（）被调用往往比它应该是...任何人都知道我怎样才能让我的GridView的图像停止重新加载，同时保持滚动性能？

在此先感谢。

来源

2012-03-07 ImNotAnUser

问题解决了，必须检查异步任务开始时的图像是否与onPostExecute（）结束时的图像相同。

新bindView：

@Override 
    public void bindView(View view, Context context, Cursor cursor) { 

     ViewHolder holder = (ViewHolder) view.getTag(); 
     holder.thumbImg.setId(cursor.getPosition()); 
     ImageThumbnailLoader imageLoader = new ImageThumbnailLoader(holder.thumbImg, 
      context.getContentResolver()); 
     imageLoader.execute(cursor.getLong(mColumnID)); 
    Log.i("Prototype", "bindView : " + cursor.getPosition()); 
    }

新的异步：

public class ImageThumbnailLoader extends AsyncTask<Long, Void, Bitmap> { 

    private final Options mOptions; 

    private WeakReference<ImageView> mImageViewWeakReference; 
    private ContentResolver mContentResolver; 
    private int mPosition; 


     public ImageThumbnailLoader(ImageView imageView, 
      ContentResolver cr) { 
     mContentResolver = cr; 
     mImageViewWeakReference = new WeakReference<ImageView>(imageView); 
     mOptions = new Options(); 
     mOptions.inSampleSize = 4; 
     mPosition = imageView.getId(); 
    } 



    @Override 
    protected Bitmap doInBackground(Long... params) { 
     Bitmap result; 
      result = MediaStore.Images.Thumbnails.getThumbnail(
       mContentResolver, params[0], 
       MediaStore.Images.Thumbnails.MINI_KIND, mOptions); 
     return result; 
    } 

    @Override 
    protected void onPostExecute(Bitmap result) { 
     super.onPostExecute(result); 
      if (mImageViewWeakReference != null 
        && mImageViewWeakReference.get() != null 
         && mPosition == mImageViewWeakReference.get().getId()) 
       mImageViewWeakReference.get().setImageBitmap(result); 
    } 

}

来源

2012-03-09 17:03:25 ImNotAnUser

使用asynctask从内容提供商加载图像位图

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