android中的Uri vs File vs StringPath

Question

if (requestCode == RESULT_LOAD_IMAGE && resultCode == RESULT_OK && null != data) { //Browse Gallery is requested
    //Get the path for selected image in Gallery
    Uri selectedImage = data.getData();
    String[] filePathColumn = { MediaStore.Images.Media.DATA };

    //Access Gallery according to the path
    Cursor cursor = getContentResolver().query(selectedImage, filePathColumn, null, null, null);
    cursor.moveToFirst();

    int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
    String picturePath = cursor.getString(columnIndex);
    cursor.close();

    loadImage(picturePath);         //load picture according the path
    image_View.setImageBitmap(pic); //Show the selected picture
}

private void loadImage(String picturePath) {
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;

    BitmapFactory.decodeFile(picturePath,options);
    int height_ = options.outHeight;
    int width_ = options.outWidth;
    float ratio = width_/height_;
    int width = 480;
    int height = 480;
    if(width_>height_){
        height = Math.round(width / ratio);
    }else{
        width = Math.round(width*ratio);
    }

    options.inSampleSize = calculateInSampleSize(options, width, height);
    options.inJustDecodeBounds = false;
    pic=BitmapFactory.decodeFile(picturePath,options);
}

File cacheDir = getBaseContext().getCacheDir();
//Form a directory with a file named "pic"
File f = new File(cacheDir, "pic");

try {
    //Prepare output stream that write byte to the directory
    FileOutputStream out = new FileOutputStream(f);
    //Save the picture to the directory
    pic.compress(Bitmap.CompressFormat.JPEG, 100, out);
    out.flush();
    out.close();
} catch (FileNotFoundException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

那么，有什么区别呢？是不是只是用法不同，却代表相同的目录？

Answer 1

内容URI类似于：

content://media/external/images/media/53

ContentResolver在这里的作用是根据这个URI获得对映像的访问权，您不需要知道文件名或文件的其他属性，只需要这个URI就可以访问映像。

String Path是存储的映像的物理地址，看起来如下所示：

file:///mnt/sdcard/myimage.jpg

在您提供的示例中,以下是进度：

1-您要求ContentResolver根据提供的URI给出真实的文件路径

2-根据提供的路径将位图文件加载到pic对象