How to add a button programmatically to a fragment

Question

I can't manage to add programmatically a button to a fragment. (The number of buttons is variable)

I tried to add the button to the rootView with "an" addView method, but there isn't one.

I tried to add the button to the layout before inflating it, but I don't know how to get the layout : (Expected resource of type id error)

RelativeLayout rl = getView().findViewById(R.layout.fragment_main);

But when the inflater inflates it, the resource is good.

I tried to add the button in the "onViewCreated" method, but I got the same problem with findViewById(R.layout.fragment_main) telling me there is an error (Expected resource of type id).

When I create a button like this :

Button bt = new Button(this);

"this" is not a valid context. Don't know what to use instead.

So, how can I achieve it ?

The base code :

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (savedInstanceState == null) {
        getFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment())
                .commit();
    }
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        return rootView;
    }
}
}

Activity_main.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    tools:ignore="MergeRootFrame" />

Fragment_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity$PlaceholderFragment">

    <TextView
        android:text="@string/hello_world"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</RelativeLayout>

Answer 1

You can use the view's context to create the button:

public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
     View view = inflater.Inflate(Resource.Layout.fragment_question_list, container, false);

     Button btn = new Button(view.Context);

     return view
}

Answer 2

I tried to add the button to the layout before inflating it, but I don't know how to get the layout : (Expected resource of type id error)

Your code should be casting it to a relative layout and looking for a resource ID not a layout file.

RelativeLayout rl = (RelativeLayout) getView().findViewById(R.id.fragment_main_layout);

Hope this helps

Answer 3

There are a few thing to correct in your code, on the fragment_main.xml:

If you want to access an element on an xml, you need to give it a unique id. In the case of your relative layout you are missing it and therefore you won't be able to find it on the fragment view.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/fragment_main_layout"     <!--some id-->
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity$PlaceholderFragment">

    <TextView
        android:text="@string/hello_world"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</RelativeLayout>

Now in your fragment class you can find it!

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

    //Find the layout with the id you gave in on the xml
    RelativeLayout rl = (RelativeLayout) rootView.findViewById(R.id.fragment_main_layout);

   //And now you can add the buttons you need, because it's a fragment, use getActivity() as context
   Button bt = new Button(getActivity());
   //You can add LayoutParams to put the button where you want it and the just add it
   rl.addView(bt);


    return rootView;
}

And that's it, you have a new button on your layout