问题

How can I get the context in a fragment?

I need to use my database whose constructor takes in the context, but getApplicationContext() and FragmentClass.this don\'t work so what can I do?

Database constructor

public Database(Context ctx)
{
    this.context = ctx;
    DBHelper = new DatabaseHelper(context);
}

回答1:

You can use getActivity(), which returns the activity associated with a fragment.
The activity is a context (since Activity extends Context).

回答2:

To do as the answer above, you can override the onAttach method of fragment:

public static class DummySectionFragment extends Fragment{
...
    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        DBHelper = new DatabaseHelper(activity);
    }
}

回答3:

Always use the getActivity() method to get the context of your attached activity, but always remember one thing: Fragments are slightly unstable and getActivity returns null some times, so for that, always check the isAdded() method of fragment before getting context by getActivity().

回答4:

The easiest and most precise way to get the context of the fragment that I found is to get it directly from the ViewGroup when you call onCreateView method at least here you are sure not to get null for getActivity():

public class Animal extends Fragment { 
  Context thiscontext;
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
  {
    thiscontext = container.getContext();

回答5:

@Override
public void onAttach(Activity activity) {
    // TODO Auto-generated method stub
    super.onAttach(activity);
    context=activity;
}

回答6:

Previously I'm using onAttach (Activity activity) to get context in Fragment

Problem

The onAttach (Activity activity) method was deprecated in API level 23.

Solution

Now to get context in Fragment we can use onAttach (Context context)

onAttach (Context context)

Called when a fragment is first attached to its context. onCreate(Bundle) will be called after this.

Documentation

/**
 * Called when a fragment is first attached to its context.
 * {@link #onCreate(Bundle)} will be called after this.
 */
@CallSuper
public void onAttach(Context context) {
    mCalled = true;
    final Activity hostActivity = mHost == null ? null : mHost.getActivity();
    if (hostActivity != null) {
        mCalled = false;
        onAttach(hostActivity);
    }
}

SAMPLE CODE

public class FirstFragment extends Fragment {


    private Context mContext;
    public FirstFragment() {
        // Required empty public constructor
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        mContext=context;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rooView=inflater.inflate(R.layout.fragment_first, container, false);

        Toast.makeText(mContext, "THIS IS SAMPLE TOAST", Toast.LENGTH_SHORT).show();
        // Inflate the layout for this fragment
        return rooView;
    }

}

NOTE

We can also use getActivity() to get context in Fragments but getActivity() can return null if the your fragment is not currently attached to a parent activity,

回答7:

Another alternative approach is:

You can get the context using:

getActivity().getApplicationContext();

回答8:

to get the context inside the Fragment will be possible using getActivity() :

public Database()
{
    this.context = getActivity();
    DBHelper = new DatabaseHelper(this.context);
}

Be careful, to get the Activity associated with the fragment using getActivity(), you can use it but is not recommended it will cause memory leaks.

I think a better aproach must be getting the Activity from the onAttach() method:

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    context = activity;
}

回答9:

You could also get the context from the inflater parameter, when overriding onCreateView.

public static class MyFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
        /* ... */
        Context context = inflater.getContext();
        /* ... */
    }
}

回答10:

getContext() came in API 23. Replace it with getActivity() everywhere in the code.

See if it fixes the error. Try to use methods which are in between the target and minimun API level, else this error will come in place.

回答11:

Since API level 23 there is getContext() but if you want to support older versions you can use getActivity().getApplicationContext() while I still recommend using the support version of Fragment which is android.support.v4.app.Fragment.

回答12:

getActivity() is a child of Context so that should work for you

回答13:

Use fragments from Support Library -

android.support.v4.app.Fragment

and then override

void onAttach (Context context) {
  this.context = context;
}

This way you can be sure that context will always be a non-null value.

回答14:

You have different options:

If your minSDK <= 21, then you can use getActivity(), since this is a Context.
If your minSDK is >=23, then you can use getContext().

If you don't need to support old versions then go with getContext().

回答15:

For Kotlin you can use context directly in fragments. But in some cased you will find an error like

Type mismatch: inferred type is Context? but Context was expected

for that you can do this

val ctx = context ?: return
textViewABC.setTextColor(ContextCompat.getColor(ctx, android.R.color.black))

回答16:

Ideally, you should not need to use globals. The fragment has different notifications, one of them being onActivityCreated. You can get the instance of the activity in this lifecycle event of the fragment.

Then: you can dereference the fragment to get activity, context or applicationcontext as you desire:

this.getActivity() will give you the handle to the activity this.getContext() will give you a handle to the context this.getActivity().getApplicationContext() will give you the handle to the application context. You should preferably use the application context when passing it on to the db.

回答17:

The simple way is to use getActivity(). But I think the major confusion of using the getActivity() method to get the context here is a null pointer exception.

For this, first check with the isAdded() method which will determine whether it's added or not, and then we can use the getActivity() to get the context of Activity.

回答18:

You can call getActivity() or,

public void onAttach(Context context) {
    super.onAttach(context);
    this.activity = (CashActivity) context;
    this.money = this.activity.money;
}

回答19:

In kotlin just use activity instead of getActivity()

回答20:

getContext() method helps to use the Context of the class in a fragment activity.

回答21:

I think you can use

public static class MyFragment extends Fragment {
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

      Context context = getActivity.getContext();

  }
}

回答22:

public class MenuFragment extends Fragment implements View.OnClickListener {
    private Context mContext;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        FragmentMenuBinding binding=FragmentMenuBinding.inflate(inflater,container,false);
        View view=binding.getRoot();
        mContext=view.getContext();
        return view;
    }
}

回答23:

Also you can use:

inflater.getContext();

but I would prefer to use

getActivity()

getContext

回答24:

I need context for using arrayAdapter IN fragment, when I was using getActivity error occurs but when i replace it with getContext it works for me

listView LV=getView().findViewById(R.id.listOFsensors);
LV.setAdapter(new ArrayAdapter<String>(getContext(),android.R.layout.simple_list_item_1 ,listSensorType));

回答25:

You can use `getActivity()` or `getContext` in Fragment.

Documentation

/**
 * Return the {@link FragmentActivity} this fragment is currently associated with.
 * May return {@code null} if the fragment is associated with a {@link Context}
 * instead.
 *
 * @see #requireActivity()
 */
@Nullable
final public FragmentActivity getActivity() {
    return mHost == null ? null : (FragmentActivity) mHost.getActivity();
}

and

 /**
     * Return the {@link Context} this fragment is currently associated with.
     *
     * @see #requireContext()
     */
    @Nullable
    public Context getContext() {
        return mHost == null ? null : mHost.getContext();
    }

Pro tip

Check always if(getActivity!=null) because it can be null when fragment is not attached to activity. Sometimes doing long operation in fragment (like fetching data from rest api) takes some time. and if user navigate to another fragment. Then getActivity will be null. And you will get NPE if you did not handle it.

回答26:

On you fragment

((Name_of_your_Activity) getActivity()).helper

On Activity

DbHelper helper = new DbHelper(this);

回答27:

You can use getActivity() method to get context or You can use getContext() method .

 View root = inflater.inflate(R.layout.fragment_slideshow, container, false);
    Context c = root.getContext();

I hope it helps!

来源：https://stackoverflow.com/questions/8215308/using-context-in-a-fragment

标签

java

android

android-fragments

android-context

Using context in a fragment

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