更新代码以包括错误处理和工作线程

Question

我是安卓开发的新手。我希望将下面的代码（用于查询媒体集合）更新为包含用于错误处理的 try 和 catch 块，以及在工作线程中调用的 query() 方法。

public void getAllImages(){
        Uri imageCollection;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            imageCollection = MediaStore.Images.Media.getContentUri(MediaStore.VOLUME_EXTERNAL);
        } else {
            imageCollection = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
        }
 
        String[] projection = new String[] {
                MediaStore.Images.Media._ID,
                MediaStore.Images.Media.DISPLAY_NAME,
                MediaStore.Images.Media.DATE_ADDED,
                MediaStore.Images.Media.SIZE
        };
 
        String sortOrder = MediaStore.Images.Media.DATE_ADDED + " DESC";
 
        Cursor cursor = getActivity().getContentResolver().query(imageCollection , projection, null, null, sortOrder);
        int idColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media._ID);
        int nameColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DISPLAY_NAME);
        int dateColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATE_ADDED);
        int sizeColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.SIZE);
 
        while (cursor.moveToNext()) {
            long id = cursor.getLong(idColumn);
            String name = cursor.getString(nameColumn);
            int duration = cursor.getInt(dateColumn);
            int size = cursor.getInt(sizeColumn);
            Uri uriImage = Uri.withAppendedPath(imageCollection, ""+ id);
            ImageModel imageModel = new ImageModel();
            imageModel.setImage(uriImage);
            imageList.add(imageModel);
        }
        cursor.close();

Answer 1

Cursor 上方的代码不会以其当前格式引发异常。甚至 由于MediaStore.VOLUME_EXTERNAL 不是null，MediaStore.Images.Media.getContentUri(MediaStore.VOLUME_EXTERNAL); 不会抛出异常。

下一步是将其余代码封装在 try-catch-finally 中，然后将其封装在 Thread.run() 调用中。

Thread thread = new Thread() {
    public void run() {
        Cursor cursor = null;
        try {
            cursor = getActivity().getContentResolver().query(imageCollection, projection, null, null, sortOrder);
            int idColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media._ID);
            int nameColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DISPLAY_NAME);
            int dateColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATE_ADDED);
            int sizeColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.SIZE);

            while (cursor.moveToNext()) {
                long id = cursor.getLong(idColumn);
                String name = cursor.getString(nameColumn);
                int duration = cursor.getInt(dateColumn);
                int size = cursor.getInt(sizeColumn);
                Uri uriImage = Uri.withAppendedPath(imageCollection, "" + id);
                ImageModel imageModel = new ImageModel();
                imageModel.setImage(uriImage);
                imageList.add(imageModel);
            }
            cursor.close();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }
    }
}
//Start the thread
thread.start();

现在有很多其他方法可以使用后台线程来产生比仅使用 Thread 更好的流，包括 Worker（来自 jetpack）、RxJava 和 Guava。如果使用 Kotlin，还有 coroutines。

https://developer.android.com/reference/androidx/work/Worker

https://github.com/ReactiveX/RxJava

https://github.com/google/guava/wiki/ListenableFutureExplained