Trying to create a custom layout that extends constraintlayout

Janko92 :

So I've this custom layout.

public class MyCustomView extends ConstraintLayout {
    private Button myFancyButton;
    public MyCustomView (@NonNull Context context, AttributeSet attrs) {
        super(context,attrs);
    myFancyButton = findViewById(R.id.button); //THIS IS NULL
    }
    public void init(){
    myFancyButton = findViewById(R.id.button); //WORKS GREAT
    }
}

The problem is I would rather not create a function "init" to do the work that is suited for a constructor. The issue I'm facing is calling findViewById in the constructor causes it to be null. Using the init function on a MyCustomView object works just fine. But I much rather do this in the constructor.

The corresponding XML file looks as follows.

<?xml version="1.0" encoding="utf-8"?>
<se.test.test.test.MyCustomView xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="wrap_content"
    android:layout_width="match_parent">

        <Button
            android:id="@+id/button"
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:text="B1"
            android:textSize="30sp"/>

</se.test.test.test.MyCustomView>

Froyo :

You need to put that code in onFinishInflate() - That method is called when the layout and its children are inflated.

@Override
public void onFinishInflate() {
    myFancyButton = findViewById(R.id.button)
}

https://developer.android.com/reference/android/view/View#onFinishInflate()