如何从Main活动中调用片段的功能

Question

First let me tell you what I am trying to do. I have an activity with navigation drawer and some fragment classes. On activity resume I am calling a MapFragment which I am using to show the user its current location with the blue dot on google map.

This is running successfully .

Now from the navigation drawer I want to show the pins on the map , so for this I am calling the function which is used to download pins from the server and to show them on map. This function is named as GetAllPins , I am doing this in the following manner using Ion library:

 public void GetAllPins() {

        progressDialog.show();
 Ion.with(getActivity())
                .load(MyServiceUrl)
                .progressHandler(new ProgressCallback() {
                    @Override
                    public void onProgress(long downloaded, long total) {
                        if (downloaded == total) {
                            progressDialog.dismiss();
                        }
                    }
                })
                .setMultipartParameter("name", "Stacy")
                .setMultipartParameter("latitude","18.92239u")
                .setMultipartParameter("longitude", "24.98329")
                .asJsonObject()
                .setCallback(new FutureCallback<JsonObject>() {
                    @Override
                    public void onCompleted(Exception e, JsonObject result) {
                        if (result == null) {
                            progressDialog.dismiss();
                            Toast.makeText(getActivity(), "Error in establishing connection with server", Toast.LENGTH_SHORT).show();

                        } else {
                            Toast.makeText(getActivity(), "Completed successfully", Toast.LENGTH_SHORT).show();
}
}
);
}

Note : This is working fine and plotting pins successfully when called inside MyMapFragment's onActivityCreated Method , but giving me a NullpointerException when I try to call it from the MainActivity.

In MainActivity I am calling it in switch case as I am using SwitchCase to navigate to fragments accordingly .

public void navigateToFragment(int pos) {

    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    final MyMapFragment myMapFragment = new MyMapFragment();
    switch (pos) {


        case R.id.home:
            if(!isFirstRun) {

                fragmentTransaction.replace(R.id.frame, myMapFragment, "MapFragment").addToBackStack("MapFragment").commit();
            }else{
                isFirstRun=false;
            }
            //
            break;

        case R.id.mark_pin:
            isFirstRun=false;
            if (myMapFragment!=null){
           myMapFragment.GetAllPins();}
                        break;
                    }

So I am getting a Null pointerException on ProgressDialog , but if I comment out the following an error occures.

 FATAL EXCEPTION: main
java.lang.NullPointerException: Can not pass null context in to retrieve ion instance

Tell me how to call this function from the main activity to show the pins on the map using that MyMapFragment. I do not want to make a different fragment of map to show the pins on it. Please help me.

Answer 1

From the log itself, itz clear that the error iz where the context is called... From fragment, u will get proper context when you call getActivity()... But when u call the same method from MainActivity, the getActivity() will return null... So itz better to add context as a parameter to the function and when calling from fragment, call it by passing getActivity() and from MainActivity call it by passing 'this'...

I didnt Test it... But it should work...

Call the function from MainActivity like this, fragment.GetAllPins(MainActivity.this);

When u call from fragment, it should be like this, GetAllPins(getActivity());