在公共共享存储上操作图片的典型代码示例:

void createExternalStoragePublicPicture() {
    // Create a path where we will place our picture in the user's
    // public pictures directory.  Note that you should be careful about
    // what you place here, since the user often manages these files.  For
    // pictures and other media owned by the application, consider
    // Context.getExternalMediaDir().

    File path = Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES);
    File file = new File(path, "DemoPicture.jpg");

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

        // Very simple code to copy a picture from the application's
        // resource into the external file.  Note that this code does
        // no error checking, and assumes the picture is small (does not
        // try to copy it in chunks).  Note that if external storage is
        // not currently mounted this will silently fail.
        InputStream is = getResources().openRawResource(R.drawable.balloons);
        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(this,
                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) {
        // Unable to create file, likely because external storage is
        // not currently mounted.
        Log.w("ExternalStorage", "Error writing " + file, e);
    }
}


//删除共享内存中的图片
void deleteExternalStoragePublicPicture() {
    // Create a path where we will place our picture in the user's
    // public pictures directory and delete the file.  If external
    // storage is not currently mounted this will fail.

    File path = Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES);
    File file = new File(path, "DemoPicture.jpg");
    file.delete();
}

//判断共享内存中是否有该图片
boolean hasExternalStoragePublicPicture() {
    // Create a path where we will place our picture in the user's
    // public pictures directory and check if the file exists.  If
    // external storage is not currently mounted this will think the
    // picture doesn't exist.
    File path = Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES);
    File file = new File(path, "DemoPicture.jpg");
    return file.exists();
}