Android中关于外部储存的一些重要函数

void createExternalStoragePrivateFile() {
    /* Create a path where we will place our private file on external
     storage.
     */
    File file = new File(getExternalFilesDir(null), "DemoFile.jpg");
    try {
        /* 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();
    } catch (IOException e) {
        /* Unable to create file, likely because external storage is
          not currently mounted.
        */
        Log.w("ExternalStorage", "Error writing " + file, e);
    }
}
void deleteExternalStoragePrivateFile() {
    /* Get path for the file on external storage.  If external
      storage is not currently mounted this will fail.
     */
    File file = new File(getExternalFilesDir(null), "DemoFile.jpg");
    if (file != null) {
        file.delete();
    }
}
boolean hasExternalStoragePrivateFile() {
    /* Get path for the file on external storage.  If external
       storage is not currently mounted this will fail.
    */
    File file = new File(getExternalFilesDir(null), "DemoFile.jpg");
    if (file != null) {
        return file.exists();
    }
    return false;
}

If you supply a non-null type to this function, the returned file will be a path to a sub-directory of the given type. Though these files are not automatically scanned by the media scanner, you can explicitly add them to the media database with MediaScannerConnection.scanFile. Note that this is not the same asEnvironment.getExternalStoragePublicDirectory(), which provides directories of media shared by all applications. The directories returned here are owned by the application, and their contents will be removed when the application is uninstalled. UnlikeEnvironment.getExternalStoragePublicDirectory(), the directory returned here will be automatically created for you.

Here is an example of typical code to manipulate a picture in an application's private storage and add it to the media database:

void createExternalStoragePrivatePicture() {
    /* Create a path where we will place our picture in our own private
       pictures directory.  Note that we don't really need to place a
       picture in DIRECTORY_PICTURES, since the media scanner will see
       all media in these directories; this may be useful with other
       media types such as DIRECTORY_MUSIC however to help it classify
       your media for display to the user.
    */
    File path = getExternalFilesDir(Environment.DIRECTORY_PICTURES);
    File file = new File(path, "DemoPicture.jpg");
    try {
        /* 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);
    }
}
void deleteExternalStoragePrivatePicture() {
    /* 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 = getExternalFilesDir(Environment.DIRECTORY_PICTURES);
    if (path != null) {
        File file = new File(path, "DemoPicture.jpg");
        file.delete();
    }
}
boolean hasExternalStoragePrivatePicture() {
    /* 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 = getExternalFilesDir(Environment.DIRECTORY_PICTURES);
    if (path != null) {
        File file = new File(path, "DemoPicture.jpg");
        return file.exists();
    }
    return false;
}

public static File getExternalStorageDirectory ()

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);
    }
}
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();
}
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();

public static String getExternalStorageState ()