Android教程-setImageResource和网格视图

我通过以下教程实现了网格视图：

适配器引用了以下图片：

// references to our images
private Integer[] mThumbIds = {
        R.drawable.sample_2, R.drawable.sample_3,
        R.drawable.sample_4, R.drawable.sample_5,
        R.drawable.sample_6, R.drawable.sample_7,
        R.drawable.sample_0, R.drawable.sample_1,
        R.drawable.sample_2, R.drawable.sample_3,
        R.drawable.sample_4, R.drawable.sample_5,
        R.drawable.sample_6, R.drawable.sample_7,
        R.drawable.sample_0, R.drawable.sample_1,
        R.drawable.sample_2, R.drawable.sample_3,
        R.drawable.sample_4, R.drawable.sample_5,
        R.drawable.sample_6, R.drawable.sample_7
};

然后使用setImageResource显示图片：

imageView.setImageResource(mThumbIds[position]);

我想改进这一点，并且…：

从internet下载图片（我将提供URI）

缓存图像

在GridView中显示它们

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我该怎么做？请为我指出正确的方向，并提供相关的教程（如果可能）

AsyncTask以在ImageView上加载图片：

private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
    private ImageView bmImage;

    public DownloadImageTask(ImageView bmImage) {
        this.bmImage = bmImage;
    }

    protected Bitmap doInBackground(String... urls) {
        final File cacheDir = getCacheDir();
        Bitmap bitmap = null;
        if (Utill.isMemoryAvaliable(dir.getPath())){
            String url = urls[0];
            String filename = url.substring(url.lastIndexOf("/")+1,url.contains("?")?url.indexOf("?"):url.length());
            File f = new File(cacheDir, filename);
            //from SD cache
            if(!f.exists()){
                try {
                    Utill.DownloadFromUrl(url, filename, cacheDir);
                } catch (IOException ex) {
                    Log.e("Error", "Download", ex);
                }
            }
            if(f.exists())
                bitmap =  decodeFile(new File(cacheDir, filename));
        }
        return bitmap;
    }

    protected void onPostExecute(Bitmap result) {
        bmImage.setImageBitmap(result);
    }

    private Bitmap decodeFile(File f) {
        try {
            BitmapFactory.Options o = new BitmapFactory.Options();
            o.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(new FileInputStream(f), null, o);
            return BitmapFactory.decodeStream(new FileInputStream(f));
        } catch (FileNotFoundException e) {
            Log.e("Error", "Decode File", e);
        }
        return null;
    }

}

• 从internet下载图片（我将提供URI）

本教程应该对您有所帮助

• 缓存图像

如果您想在一个应用程序生命周期中拥有缓存，或者创建SQLite数据库来拥有缓存，您可以在类中使用HashMap来永久存储数据

• 在GridView中显示它们

您需要扩展BaseAdapter类。本教程将帮助您：

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如果您有其他与此主题相关的问题或不清楚的问题，请提问，我将尝试帮助您编写自己的逻辑，通过网络获取数据或使用库universal image loader或Volley。我更愿意自己编写获取程序。你知道这方面有什么好的教程吗？

public static boolean downloadFromUrl(String downloadUrl, String fileName, File dir) throws IOException {
        if (URLUtil.isValidUrl(downloadUrl)) {
            System.setProperty("http.keepAlive", "false");
            URL url = new URL(downloadUrl);
            HttpURLConnection ucon = (HttpURLConnection) url.openConnection();
            ucon.setRequestProperty("Connection", "Keep-Alive");
            ucon.setConnectTimeout(50000); 
            ucon.connect();
            if (ucon.getResponseCode() == HttpURLConnection.HTTP_OK) {
                InputStream is = url.openStream();
                if (is.available() > 0) {
                    BufferedInputStream bis = new BufferedInputStream(is);
                    ByteArrayBuffer baf = new ByteArrayBuffer(5000);
                    int current = 0;
                    while ((current = bis.read()) != -1) {
                        baf.append((byte) current);
                    }
                    File file = new File(dir, fileName);
                    FileOutputStream fos = new FileOutputStream(file);
                    fos.write(baf.toByteArray());
                    fos.flush();
                    fos.close();
                }
                is.close();
                return true;
            } else {
                return false;
            }
        }
        return false;
    }