Question

我正在编写一个从服务器下载图像的Android应用程序，但我想在适配器中加载图像时显示加载图像。这是我的适配器：

public class GridViewImageAdapter extends BaseAdapter {
Context context;
public ImageView imageView;
private Activity _activity;
private ArrayList<String> _filePaths = new ArrayList<String>();
private int imageWidth;

public GridViewImageAdapter(Activity activity, ArrayList<String> filePaths,
        int imageWidth,Context context1) {

    this._activity = activity;
    this._filePaths = filePaths;
    this.imageWidth = imageWidth;
    this.context=context1;

}

public int getCount() {
    return this._filePaths.size();
}

public Object getItem(int position) {
    return this._filePaths.get(position);
}

public long getItemId(int position) {
    return position;
}

public View getView(int position, View convertView, ViewGroup parent) {

    if (convertView == null) {
        imageView = new ImageView(_activity);
    } else {
        imageView = (ImageView) convertView;
    }


    imageView.setBackgroundResource(R.drawable.gallery_image);

   imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
  imageView.setLayoutParams(new GridView.LayoutParams(imageWidth,
          imageWidth));
  Log.e("Position",position+"");
    new RetreiveBitMap().execute(_filePaths.get(position));

return imageView;
}

class RetreiveBitMap extends AsyncTask<String,Integer,Bitmap> {

    private Exception exception;
    protected Bitmap doInBackground(String... urls) {

        Bitmap bm = null;
        URL myFileUrl =null;
        BitmapFactory.Options options=new BitmapFactory.Options();
            options.inSampleSize = 1;
        try {
            myFileUrl= new URL(urls[0]);
            } catch (MalformedURLException e) {
            e.printStackTrace();
            }
        try {

            String encodedfilename = Base64.encodeToString(urls[0].getBytes(),0);

        //Controllo presenza della cache
        try {
        InputStream check = context.openFileInput(encodedfilename);
        } catch (FileNotFoundException e) {
        // Se non presente, scarico il file

        HttpURLConnection conn= (HttpURLConnection)myFileUrl.openConnection();
        conn.setDoInput(true);
        conn.connect();
        InputStream is = conn.getInputStream();
         //Salvataggio cache
        FileOutputStream fos = context.openFileOutput(encodedfilename, Context.MODE_PRIVATE);
        byte[] buffer = new byte[1024];
        int len1 = 0;
        while ( (len1 = is.read(buffer)) > 0 ) {
        fos.write(buffer,0, len1);
        }

        fos.close();
        }

         bm = BitmapFactory.decodeStream(context.openFileInput(encodedfilename),null,options);


        } catch (IOException e) {
Log.e("errore download",e.getMessage());
        } 
        return bm;

    } 
    protected void onPreExecute() {

        imageView.setImageResource(R.drawable.spinner);
    }

    protected void onPostExecute(Bitmap imageBit) {

        imageView.setImageBitmap(imageBit);
    }
}
}

此适配器显示加载图像，但只有最后一个网格更改为下载的图像，并且它位于错误的位置，因为它应该是网格的第一个。

Answer 1

您可以这样做：执行下面的onPreExecute()和onPostExecute()：

 protected void onPreExecute() {
    imageView.setImageResource(R.drawable.spinner);//Loading image 

 protected void onPostExecute(Bitmap imageBit) {

 if(imagefit!=null){
    imageView.setBitmap(imagefit);//Final image
   }
}

Answer 2

您可以 Square 使用 Picasso 库。

http://square.github.io/picasso/

该库为您提供了占位符选项，同时它还可以执行必要的网络下载图像。如果您在自定义适配器上加载图像，则无需在此处使用Asynctask。

这一行将起到作用

Picasso.with(context)
  .load(url)
  .placeholder(R.id.placeholder)
  .error(R.id.placeholder_error)
  .into(imageView)

您还可以使用.resize(width, height)和.centerCrop()或.fit()

访问调整大小选项

希望它有所帮助！

Answer 3

确定您的AsyncTask覆盖onPreExecute()和onPostExecute()就像这样

Dialog dialog;
@Override
protected void onPreExecute() {
    //initialize inflate and customize your dialog
    dialog.setMessage("Loading...");
    dialog.setIcon(R.drawable.youricon);
    dialog.setCancelable(false);
    dialog.show();
}

@Override
protected void onPostExecute(Void result) {
    if (dialog.isShowing())
        dialog.dismiss();
}

看到这个 How to create a Custom Progress Dialog over riding the default one in Android?

希望它有助于欢呼：）

Answer 4

您可以使用Universal Image Loader之类的通用图片加载库。它可以非常快速地加载图像。

Android - 如何在适配器加载图像时显示加载图像？

4 个答案: