使用asyncTask在android中的列表视图中加载图像

我目前正在使用asynctask加载图像。我参考了一个示例类。但是，该位图结果为空。为什么是这样，我该如何解决这个问题？谢谢。代码如下所示。使用asyncTask在android中的列表视图中加载图像

package com.example.json; 

import java.io.File; 

import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.os.AsyncTask; 
import android.os.Environment; 
import android.util.Log; 
import android.view.View; 
import android.widget.ImageView; 

class ImgAdapter extends AsyncTask<Object, Void, Bitmap> { 

    private ImageView imv; 
    private String path; 

    public ImgAdapter(ImageView imv) { 
     this.imv = imv; 
     this.path = imv.getTag().toString(); 
    } 

    @Override 
    protected Bitmap doInBackground(Object... params) { 
     Bitmap bitmap = null; 
     File file = new File(Environment.getExternalStorageDirectory() 
       .getAbsolutePath() + path); 

     if (file.exists()) { 
      bitmap = BitmapFactory.decodeFile(file.getAbsolutePath()); 
     } 

     return bitmap; 
    } 

    @Override 
    protected void onPostExecute(Bitmap result) { 
     if (!imv.getTag().toString().equals(path)) { 
      /* 
      * The path is not same. This means that this image view is handled 
      * by some other async task. We don't do anything and return. 
      */ 
      return; 
     } 

     if (result != null && imv != null) { 
      Log.i("test","success"); 
      imv.setVisibility(View.VISIBLE); 
      imv.setImageBitmap(result); 
     } else { 
      Log.i("test","result=" + String.valueOf(result == null)); //result is null here 
      Log.i("test","imv=" + String.valueOf(imv == null)); 
      Log.i("test","fail"); 
      imv.setVisibility(View.GONE); 
     } 
    } 
}

如何ListView控件适配器拨打：

public View getView(int arg0, View arg1, ViewGroup arg2) { 
ImageView thumbnail = (ImageView) arg1.findViewById(R.id.imageView1); 
ShopEntry entry = getItem(arg0); 
thumbnail.setTag(entry.image_url); 
new ImgAdapter(thumbnail).execute(); 
return arg1; 
}

来源

2013-07-30 user782104

检查此链接。 http://stackoverflow.com/questions/2471935/how-to-load-an-imageview-by-url-in-android –

感谢我现在读它 – user782104

不是传递的ImageView的任务，你只要需要用返回的图像填充适配器中的数据集，然后在getView中相应地更改图像。以上实现是buggy –

改变这一点：

Bitmap bitmap = null; 
     File file = new File(Environment.getExternalStorageDirectory() 
       .getAbsolutePath() + path); 

     if (file.exists()) { 
      bitmap = BitmapFactory.decodeFile(file.getAbsolutePath()); 
     }

这样：

Bitmap bitmap = ((BitmapDrawable)imv.getDrawable()).getBitmap();

来源

2013-07-30 02:24:46 fenix

感谢您的回答，但BitmapDrawable无法解析为类型？ – user782104

import android.graphics.drawable.BitmapDrawable; – fenix

使用asyncTask在android中的列表视图中加载图像

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