give width as 0dp to make sure its size is exactly as per its weight this will make sure that even if content of child views get bigger, they'll still be limited to exactly half(according to is weight)
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:weightSum="1"
>
<Button
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="click me"
android:layout_weight="0.5"/>
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="Hello World"
android:layout_weight="0.5"/>
</LinearLayout>