Android LinearLayout is not redisplayed after changing weights programmatically

Question

I am able to construct a LinearLayout of dozens of Views programmatically and to display it as the content view of an Activity. I am able to walk the LinearLayout tree and change the backgroundcolors of the Views.

And I am able to walk the tree and adjust the relative weights of the Views and display the tree using a call to setContentView() near the end of onCreate().

I have a seekBar to adjust the colors interactively, and that works. Similarly I have a seekBar to adjust the weights interactively. I know the weights are being changed correctly.

But somehow the view is not redisplayed after changing the weights interactively, whereas it is redisplayed after changing the colors interactively.

What do I have to do in order to redisplay the content view after changing the weights?

Answer 1

requestLayout() works for me

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical">
    <SeekBar
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/seek"
        android:progress="50"
        android:max="100"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:id="@+id/linear">
        <View
            android:layout_width="0dp"
            android:layout_height="20dp"
            android:layout_weight="1"
            android:id="@+id/blue"
            android:background="#00f"/>
        <View
            android:layout_width="0dp"
            android:layout_height="20dp"
            android:layout_weight="1"
            android:id="@+id/red"
            android:background="#f00"/>
    </LinearLayout>
</LinearLayout>

---

public class MainActivity extends AppCompatActivity {
    private LinearLayout linear;
    private View red;
    private View blue;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        SeekBar seek = (SeekBar) findViewById(R.id.seek);
        linear = (LinearLayout) findViewById(R.id.linear);
        red = findViewById(R.id.red);
        blue = findViewById(R.id.blue);
        seek.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                ((LinearLayout.LayoutParams) red.getLayoutParams()).weight = 100 - progress;
                ((LinearLayout.LayoutParams) blue.getLayoutParams()).weight = progress;

                linear.requestLayout();
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        });
    }
}