Question

我的活动中有两个片段：Fragment_A和Fragment_B。

在片段A中，我创建了一个AsyncTask（当用户“ swipeRefreshes”屏幕时）。在此任务的onPostExecute()中，我想显示一个Toast：

private class MakeRequestTask extends AsyncTask<Void, Void, List<String>> {
    private Exception mLastError = null;

    MakeRequestTask() {
        //Some stuff
    }

    @Override
    protected List<String> doInBackground(Void... params) {
        //Some stuff
    }

    @Override
    protected void onPreExecute() {
        //Some stuff
    }

    @Override
    protected void onPostExecute(List<String> output) {
        swipeRefreshLayout.setRefreshing(false);
        Toast.makeText(getActivity(), "TO_DISPLAY", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onCancelled() {
        swipeRefreshLayout.setRefreshing(false);
        //Some stuff
    }
}

如果用户在AsyncTask完成之前从Fragment_A更改为Fragment_B，则会崩溃：

java.lang.IllegalStateException:片段Fragment_A未附加到上下文。

我知道如何避免崩溃（通过添加条件isAdded())，但我希望无论我的Activity顶部显示/显示哪个片段，都显示我的Toast。

Answer 1

尝试这种方式在Fragment_A中声明布尔值

private boolean isFragmentVisible=false;

在Fragment_A类中

在此onCreateView()的{{1}}中将此布尔值设为true

Fragment_A

然后将此片段A的@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // Inflate the layout for this fragment view = inflater.inflate(R.layout.lyourlayout, container, false); isFragmentVisible = true; return view; }中的布尔值设为false

onDestroyView()

最终在@Override public void onDestroyView() { super.onDestroyView(); isFragmentVisible = false; }的Asyntask中使用它

Fragment_A

Answer 2

首先，我想建议您，请使您的MakeRequestTask内部类为静态类，因为这可能会导致内存泄漏。对于您的问题，您需要将上下文传递给此类，如下所示：

    private static class MakeRequestTask extends AsyncTask<Void, Void, List<String>> {
        private Exception mLastError = null;
        private WeakReference<Context> weakReference;

        MakeRequestTask(Context context) {
            //Some stuff
            weakReference = new WeakReference<>(context);
        }

        @Override
        protected List<String> doInBackground(Void... params) {
            //Some stuff
        }

        @Override
        protected void onPreExecute() {
            //Some stuff
        }

        @Override
        protected void onPostExecute(List<String> output) {
// swipe layout will not be shown if fragment is not visible or destroyed
            if (isFragmentVisible) {
                swipeRefreshLayout.setRefreshing(false);
            }
// toast will be shown no matter what fragment is visible
            if (weakReference != null) {
                Context context = weakReference.get();
                if (context != null) {
                    Toast.makeText(context, "TO_DISPLAY", Toast.LENGTH_SHORT).show();
                }
            }
        }

        @Override
        protected void onCancelled() {
            if (isFragmentVisible) {
                swipeRefreshLayout.setRefreshing(false);
            }
            //Some stuff
        }
    }

Answer 3

或者您也可以在interface方法中使用和EventBus或onPostExecute，并在活动中显示Toast。

@Override
    protected void onPostExecute(List<String> output) {
        swipeRefreshLayout.setRefreshing(false);
        activityContractInterface.showToast()
        }
    }

在您的活动中：

@Override
public void showToast(){
     Toast.makeText(getActivity(), "TO_DISPLAY", Toast.LENGTH_SHORT).show();
}

或者使用EventBus方法：

@Override
        protected void onPostExecute(List<String> output) {
            swipeRefreshLayout.setRefreshing(false);
            EventBus.getDefault().post(new ShowToastEvent()) 
//just create an empty class, hope you know what EventBus is
            }

在您的活动中：

@Subscribe(threadMode = ThreadMode.Main){
 Toast.makeText(getActivity(), "TO_DISPLAY", Toast.LENGTH_SHORT).show();
}

EventBusLibrary

片段更改后，在OnPostExecute（）中敬酒

3 个答案: