GDK android 相机示例如何工作？

Question

所以我对这段代码（在processPictureWhenReady() 内部）末尾发生的事情有点困惑。在调用此方法之前（在onActivityResult() 内）我们有图像文件路径......所以文件已经被存储了。然后，我们使用图像的文件路径 (picturePath) 来声明文件 pictureFile。有人可以解释为什么我们必须使用相同的文件路径声明一个文件，尽管该文件已经存在？请不要只是将我转回 Google 开发者网站，因为我发现这没有用。

private static final int TAKE_PICTURE_REQUEST = 1;

private void takePicture() {
    Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    startActivityForResult(intent, TAKE_PICTURE_REQUEST);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == TAKE_PICTURE_REQUEST && resultCode == RESULT_OK) {
        String thumbnailPath = data.getStringExtra(Intents.EXTRA_THUMBNAIL_FILE_PATH);
        String picturePath = data.getStringExtra(Intents.EXTRA_PICTURE_FILE_PATH);

        processPictureWhenReady(picturePath);
        // TODO: Show the thumbnail to the user while the full picture is being
        // processed.
    }

    super.onActivityResult(requestCode, resultCode, data);
}

private void processPictureWhenReady(final String picturePath) {
    final File pictureFile = new File(picturePath);

    if (pictureFile.exists()) {
        // The picture is ready; process it.
    } else {
        // The file does not exist yet. Before starting the file observer, you
        // can update your UI to let the user know that the application is
        // waiting for the picture (for example, by displaying the thumbnail
        // image and a progress indicator).

        final File parentDirectory = pictureFile.getParentFile();
        FileObserver observer = new FileObserver(parentDirectory.getPath(),
            FileObserver.CLOSE_WRITE | FileObserver.MOVED_TO) {
            // Protect against additional pending events after CLOSE_WRITE
            // or MOVED_TO is handled.
            private boolean isFileWritten;

        @Override
        public void onEvent(int event, String path) {
            if (!isFileWritten) {
                // For safety, make sure that the file that was created in
                // the directory is actually the one that we're expecting.
                File affectedFile = new File(parentDirectory, path);
                isFileWritten = affectedFile.equals(pictureFile);

                if (isFileWritten) {
                    stopWatching();

                    // Now that the file is ready, recursively call
                    // processPictureWhenReady again (on the UI thread).
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            processPictureWhenReady(picturePath);
                        }
                    });
                }
            }
        }
    };
    observer.startWatching();
}
}

Answer 1

我猜你指的是这一行：

final File pictureFile = new File(picturePath);

他们所做的是从存储该图像的文件路径创建一个File 对象的实例。这个File 对象是他们需要对图像进行一些处理的对象。 File 对象是内存中图像文件的抽象，不是实际的物理文件。据我了解，您似乎误会了两者。