如何保存在外部存储卡中？

Question

我已经构建了一个安卓应用程序，我已经实现了保存选项，但是它保存在我的内部存储器中，我如何将它保存在我的外部存储器中？

我的保存代码---

else if(view.getId()==R.id.save_btn){
        //save drawing
        AlertDialog.Builder saveDialog = new AlertDialog.Builder(this);
        saveDialog.setTitle("Save drawing");
        saveDialog.setMessage("Save drawing to device Gallery?");
        saveDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener(){
            public void onClick(DialogInterface dialog, int which){
                //save drawing
                drawView.setDrawingCacheEnabled(true);
                //attempt to save
                String imgSaved = MediaStore.Images.Media.insertImage(
                        getContentResolver(), drawView.getDrawingCache(),
                        UUID.randomUUID().toString()+".png", "drawing");
                //feedback
                if(imgSaved!=null){
                    Toast savedToast = Toast.makeText(getApplicationContext(), 
                            "Drawing saved to Gallery!", Toast.LENGTH_SHORT);
                    savedToast.show();
                }
                else{
                    Toast unsavedToast = Toast.makeText(getApplicationContext(), 
                            "Oops! Image could not be saved.", Toast.LENGTH_SHORT);
                    unsavedToast.show();
                }
                drawView.destroyDrawingCache();
            }
        });
        saveDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener(){
            public void onClick(DialogInterface dialog, int which){
                dialog.cancel();
            }
        });
        saveDialog.show();
    }

Answer 1

首先确保您包含正确的权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

这将为您提供写入和读取权限。 接下来，检查是否可以使用外部存储：

/* Checks if external storage is available for read and write */
public boolean isExternalStorageWritable() {
    String state = Environment.getExternalStorageState();
    return Environment.MEDIA_MOUNTED.equals(state);
}

/* Checks if external storage is available to at least read */
public boolean isExternalStorageReadable() {
    String state = Environment.getExternalStorageState();
    return Environment.MEDIA_MOUNTED.equals(state) ||
        Environment.MEDIA_MOUNTED_READ_ONLY.equals(state);
}

现在选择是否要保存到公共目录：

public File getPublicStorageDir(String directory) {
    // Get the directory for the user's public pictures directory. 
    File file = new File(Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES), directory);
    if (!file.mkdirs()) {
        Log.e(LOG_TAG, "Directory not created");
    }
    return file;
}

或私有目录：

public File getPrivateStorageDir(Context context, String directory) {
    // Get the directory for the app's private pictures directory. 
    File file = new File(context.getExternalFilesDir(
            Environment.DIRECTORY_PICTURES), directory);
    if (!file.mkdirs()) {
        Log.e(LOG_TAG, "Directory not created");
    }
    return file;
}

一旦你有了包含目录的文件对象，你就可以实际保存：

private void saveToFile(File directory, String toWrite) {
    File file = new File(dir, "myData.txt");
    try {
        FileOutputStream f = new FileOutputStream(file);
        PrintWriter pw = new PrintWriter(f);
        pw.print(toWrite);
        pw.flush();
        pw.close();
        f.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }   
}

或者，您可以直接保存图像：

private void saveImage(Bitmap finalBitmap, File dir, String fileName) {
    File file = new File (dir, fileName);
    if (file.exists ()) file.delete (); 
    try {
           FileOutputStream out = new FileOutputStream(file);
           finalBitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);
           out.flush();
           out.close();

    } catch (Exception e) {
           e.printStackTrace();
    }
}

希望这会有所帮助！

参考：
http://developer.android.com/training/basics/data-storage/files.html
Write a file in external storage in Android
Android saving file to external storage