Question

我有一个Indeterminate进度条替换我的MenuItem刷新按钮，而AsyncTask加载数据。所有这些都没有问题：

我的创建选项菜单：

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {


    inflater.inflate(R.menu.videos, menu);
    menuItem = menu.findItem(R.id.button_refresh);
    super.onCreateOptionsMenu(menu, inflater);

}

异步任务：

class ReviewLoaderAsyncTask extends AsyncTask<Void, Void, ArrayList<Review>> implements Api {

    private Context context;
    private int offset;
    private FragmentCallback mFragmentCallback;
    ArrayList<Review> add;



    public ReviewLoaderAsyncTask(Context _context, int _offset, FragmentCallback _mFragmentCallback)
    {

        context = _context;
        offset = _offset;
        mFragmentCallback = _mFragmentCallback;

    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        menuItem.setActionView(R.layout.progressbar); //ERROR OCCURS HERE
        menuItem.expandActionView();
    }

    @Override
    protected ArrayList<Review> doInBackground(Void... voids) {

        // Call some data here

        return add;
    }


    @Override
    protected void onPostExecute(ArrayList<Review> _reviews) {
        super.onPostExecute(_reviews);
        menuItem.collapseActionView();
        menuItem.setActionView(null);
        mFragmentCallback.taskIsFinished(_reviews, offset);
    }


}

一切正常。但是，我想在创建视图后立即开始加载此数据。我在onCreateView部分

中执行此操作

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view  = inflater.inflate(R.layout.review_fragment_gridview, container, false);
    mGridView = (StaggeredGridView) view.findViewById(R.id.myGrid);

    reviews = new ArrayList<Review>();
    offset = 0;
    ReviewLoaderAsyncTask loadRSSTask = new ReviewLoaderAsyncTask(getActivity(), offset, new FragmentCallback() {
        @Override
        public void taskIsFinished(ArrayList<Review> add, int _offset) {
            for (Review v : add) {
                reviews.add(v);
            }
            mReviewsAdapter = new ReviewsAdapter(getActivity(), reviews, getFragmentManager());
            offset = _offset;
            mGridView.setAdapter(mReviewsAdapter);
        }
    });
    if(savedInstanceState == null){
        loadRSSTask.execute();
    } else{
        reviews = savedInstanceState.getParcelableArrayList(REVIEWS_LIST_TAG);
        ReviewsAdapter adapter = new ReviewsAdapter(getActivity(), reviews, getFragmentManager());
        mGridView.setAdapter(adapter);
        ((BaseAdapter) mGridView.getAdapter()).notifyDataSetChanged();
    }
    return view;
}

我遇到的问题是AsyncTask在菜单膨胀之前启动。当我到达AsyncTask的PreExecute部分时，这会导致NullPointerException。

是否有更好的实现方法可以在onCreateView中开始数据加载并仍然保留我的ProgressBar动作视图？

Answer 1

根据cYrixmorten的反馈，我将Async执行调用移到了onCreateOptionsMenu。这是修改后的代码。

修改onCreateView：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view  = inflater.inflate(R.layout.review_fragment_gridview, container, false);
    mGridView = (StaggeredGridView) view.findViewById(R.id.myGrid);
    bundle = savedInstanceState;
    reviews = new ArrayList<Review>();
    offset = 0;
    ReviewLoaderAsyncTask loadRSSTask = new ReviewLoaderAsyncTask(getActivity(), offset, new FragmentCallback() {
        @Override
        public void taskIsFinished(ArrayList<Review> add, int _offset) {
            for (Review v : add) {
                reviews.add(v);
            }
            System.out.println(reviews.size() +" is the video size!");
            mReviewsAdapter = new ReviewsAdapter(getActivity(), reviews, getFragmentManager());
            offset = _offset;
            mGridView.setAdapter(mReviewsAdapter);
        }
    });
    if(savedInstanceState!=null){
        reviews = savedInstanceState.getParcelableArrayList(REVIEWS_LIST_TAG);
        ReviewsAdapter adapter = new ReviewsAdapter(getActivity(), reviews, getFragmentManager());
        mGridView.setAdapter(adapter);
        ((BaseAdapter) mGridView.getAdapter()).notifyDataSetChanged();
    }
    return view;
}

修改onCreateOptionsMenu：

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {


    inflater.inflate(R.menu.videos, menu);
    menuItem = menu.findItem(R.id.button_refresh);


    ReviewLoaderAsyncTask loadRSSTask = new ReviewLoaderAsyncTask(getActivity(), offset, new FragmentCallback() {
        @Override
        public void taskIsFinished(ArrayList<Review> add, int _offset) {
            System.out.println(add.size() + "is the passed array size to the callback");
            for (Review v : add) {
                reviews.add(v);
            }
            mReviewsAdapter = new ReviewsAdapter(getActivity(), reviews, getFragmentManager());
            offset = _offset;
            mGridView.setAdapter(mReviewsAdapter);
        }
    });
    if(bundle == null){
        loadRSSTask.execute();
    }



    super.onCreateOptionsMenu(menu, inflater);

}

这是有效的，但我不会将其标记为现在的解决方案，希望能够为这个问题推广更多讨论和替代解决方案。

ActionBar初始数据加载不确定ProgressBar

1 个答案: