android - 如何从 url 下载文件/图像到你的 android 应用程序

Question

我需要我的 android 应用程序向 url 发出请求，以从此 url 下载图像所以我建立了这个类来帮助我，但它没有用 ???

public class MyAsnyc extends AsyncTask<Void, Void, Void> {
public static File file;
InputStream is;

    protected void doInBackground() throws IOException {
        File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
        file = new File(path, "DemoPicture.jpg");

        try{
            // Make sure the Pictures directory exists.
            path.mkdirs();

            URL url = new URL("http://androidsaveitem.appspot.com/downloadjpg");

            // Open a connection to that URL.
            URLConnection ucon = url.openConnection();

            // Define InputStreams to read from the URLConnection.
            is = ucon.getInputStream();
        } catch (IOException e) {
            Log.d("ImageManager", "Error: " + e);
        }
    }

    @Override
    protected Void doInBackground(Void... params) {
        try {
            doInBackground();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return null;
    }

    protected void onPostExecute() {
        try {
            OutputStream os = new FileOutputStream(file);
            byte[] data = new byte[is.available()];
            is.read(data);
            os.write(data);
            is.close();
            os.close();

            // Tell the media scanner about the new file so that it is
            // immediately available to the user.
            MediaScannerConnection.scanFile(
                null,
                new String[] { file.toString() },
                null,
                new MediaScannerConnection.OnScanCompletedListener() {
                    public void onScanCompleted(String path, Uri uri) {
                        Log.i("ExternalStorage", "Scanned " + path + ":");
                        Log.i("ExternalStorage", "-> uri=" + uri);
                    }
                }
            );
        }
        catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

我在 onclick() 的 Activity 类中有这个函数:

public void down(View v) {
    // ImageManager ob=new ImageManager();
    // ob.DownloadFromUrl("");

     new MyAsnyc().execute();
}

虽然我在manfiest.xml里面写了权限

<uses-sdk android:minSdkVersion="7" />
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
<uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Answer 1

试试这个

public class MyAsnyc extends AsyncTask<Void, Void, Void> {
    public static File file;
    InputStream is;

    protected void doInBackground() throws IOException {

        File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
        file = new File(path, "DemoPicture.jpg");
        try {    
            // Make sure the Pictures directory exists.
            path.mkdirs();

            URL url = new URL("http://androidsaveitem.appspot.com/downloadjpg");
            /* Open a connection to that URL. */
            URLConnection ucon = url.openConnection();

            /*
             * Define InputStreams to read from the URLConnection.
             */
            is = ucon.getInputStream();

            OutputStream os = new FileOutputStream(file);
            byte[] data = new byte[is.available()];
            is.read(data);
            os.write(data);
            is.close();
            os.close();

        } catch (IOException e) {
            Log.d("ImageManager", "Error: " + e);
        }
    }

    @Override
    protected Void doInBackground(Void... params) {
        // TODO Auto-generated method stub
        try {
            doInBackground();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return null;
    }

    protected void onPostExecute() {
        try {
            // Tell the media scanner about the new file so that it is
            // immediately available to the user.
            MediaScannerConnection.scanFile(null,
                    new String[]{file.toString()}, null,
                    new MediaScannerConnection.OnScanCompletedListener() {
                        public void onScanCompleted(String path, Uri uri) {
                            Log.i("ExternalStorage", "Scanned " + path + ":");
                            Log.i("ExternalStorage", "-> uri=" + uri);
                        }
                    });
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}