Android 教程 - setImageResource 和 Grid View答案

【问题标题】：Android tutorial - setImageResource and Grid ViewAndroid 教程 - setImageResource 和 Grid View
【发布时间】：2014-01-14 17:15:26
【问题描述】：

我按照本教程实现了一个网格视图：

http://developer.android.com/guide/topics/ui/layout/gridview.html

适配器参考了以下图片：

// 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]);

我想改进它并且...：

从网上下载图片（我会提供URI）
缓存图片
在 GridView 中显示它们

我该怎么做？请指出正确的方向并尽可能提供任何相关教程

【问题讨论】：

编写自己的逻辑以通过网络获取数据或使用库通用图像加载器或 volley
我更喜欢自己编写 fetcher。你知道这方面有什么好的教程吗？

标签： android gridview android-gridview android-gridlayout

【解决方案1】：

从网上下载图片（我会提供URI）

本教程应该可以帮助你https://stackoverflow.com/questions/15549421/how-to-download-and-save-an-image-in-android

缓存图片

如果您想在一个应用程序生命周期中缓存或创建 SQLite 数据库以缓存您可以永久存储数据https://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html

在 GridView 中显示它们

您需要扩展 BaseAdapter 类。本教程应该对您有所帮助：http://www.stealthcopter.com/blog/2010/09/android-creating-a-custom-adapter-for-gridview-buttonadapter/

如果您还有其他与此主题相关的问题或不清楚的地方，请提出，我会尽力帮助您

【讨论】：

【解决方案2】：

AsyncTask 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;
    }

}

要下载图片：

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;
    }

【讨论】：