初始加载Fragment时，将数据从Activity传递到Fragment

Question

So my issue is basically my MainActivity is initially loaded with a Fragment, which we will call MyFragment.

I am loading JSON, from online and wanting to pass into my MyFragment.

The problem is arising when setContentView is called in the MainActivity, it is calling onCreateView in MyFragment, which contains getArguments.getSerializable("myTag") . The key isn't passed because I haven't loaded the JSON yet.

Can you help me resolve this issue?

Here is my code:

In my MyFragment:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
        if(getArguments() != null) {
            coll = (HashSet<String>) getArguments().getSerializable("myTag");
        }
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_my, container, false);
}

MainActivity (assume I loaded my JSON already):

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    loadJSON();
    passTagsToFragment(); //passes to the fragment
}

public void passTagsToFragment(){
    Bundle bundle = new Bundle();
    bundle.putSerializable("myTags", tagsSet);
    TagsFragment frag = new MyFragment();
    frag.setArguments(bundle);
}

EDIT:

Basically, my issue is that I want to load the MainActivity fully, before even starting to load the Fragment. Not sure how to do that.

EDIT 2:

I fixed the problem here is my code: (Changed the variable names)

MainActivity.java

public TagsFragment passInfoToTagsFramgent(){
    Bundle bundle = new Bundle();
    bundle.putSerializable("tags", tagsList);
    TagsFragment frag = new TagsFragment();
    frag.setArguments(bundle);
    return frag;
}

in OnPostExecute of MainActvity.java:

Fragment tagFragment = passInfoToTagsFramgent();
                FragmentTransaction transaction  = getSupportFragmentManager().beginTransaction();
                transaction.replace(R.id.fragment_container, tagFragment);
                transaction.commit();

Answer 1

loadJSON is from online source, so I assume it is an AsyncTask.

I usually do this as a lamda expression (kotlin):

loadJSON({passTagsToFragment()})

loadJSON should take a lamda expression as parameter:

loadJSON(private val callback:()->Unit )

and in the AsyncTask::onPostExecute, you should call the callback:

callback.invoke()

or just

callback()

Then you made sure the fragment is opened when the JSON is loaded and passed to fragment.

OK let me try to make it in Java.

In your AsyncTask which loads JSON, you will need an interface eg,

public interface JSONLoadCallback {
    void loaded();
}

And the its constructor takes the interface as parameter:

class JSONLoader : AsyncTask<....> {
    JSONLoader(JSONLoadCallback callback) {
        _callback = callback;
    }
    @Override
    public void onPostExecute() {
        _callback.loaded();
    }
}

And your Activity implements JSONLoadCallback:

@Override
public void loaded() {
    passTagsToFragment();
}

And should pass itself to the AsyncTask:

JSONLoader(this).executeOnExecutor();

This way, the loaded() function is fired when JSON load is finished.

You see, Java codes are very verbal, Kotlin almost removed the necessity of Java interface.

Answer 2

You should call your passTagsToFragment() method in post execute method of your asynctask when all json data gets loaded.

 protected void onPostExecute(Long result) {
     passTagsToFragment();
 }

Answer 3

根据我的理解，您也可以在片段上调用Loadjson（）方法并相应地使用数据，但是如果您有一些特定的逻辑，则可以使用asynctask，并且在带有进度条的json检索中，可以设置任何MyFragment回调并相应地更新片段。