How to link a custom View with a custom Layout…

There are several ways:

Using a constructor with an AttributeSet attribute set: This is the most common method. In the View constructor, you can read attributes from XML markup and apply them.

public class MyCustomView extends View {

    public MyCustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // Reading attributes from attrs
        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.MyCustomView);
        // Getting attribute values, for example:
        // int someValue = a.getInt(R.styleable.MyCustomView_someAttribute, defaultValue);
        a.recycle(); // Important to free TypedArray

        // Initialize View based on read attributes
        // ...
    }

    // ... other constructors and methods
}

When defining a custom layout in XML, you can use these attributes:

<com.example.app.MyCustomView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:someAttribute="someValue" />

Inflating a layout inside a View: If the View consists of several other Views, they can be inflated from a separate XML layout file within the custom View.

public class MyCompositeView extends LinearLayout {

    public MyCompositeView(Context context, AttributeSet attrs) {
        super(context, attrs);
        LayoutInflater.from(context).inflate(R.layout.my_custom_layout, this, true);
        // Now you can find elements inside my_custom_layout
        // TextView myTextView = findViewById(R.id.myTextView);
        // ...
    }

    // ... other constructors and methods
}

my_custom_layout.xml might look like this:

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <TextView
        android:id="@+id/myTextView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Hello Custom Layout!" />

    <!-- other layout elements -->

</LinearLayout>

Then this custom layout MyCompositeView is used in another XML file:

<com.example.app.MyCompositeView
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

The choice of method depends on the complexity of the custom View: for simple Views with minimal elements, the first method is sufficient; for composite Views with internal structure, the second method is more suitable.

How to link a custom View with a custom Layout?