Android- setWidth() of Button doesn't work, if ViewGroup's width is 'match_parent'/'fill_parent' in xml?

Question

I defined a LinearLayout as root element in activity_main.xml.

CASE 1: From onCreate() I tried to add Button in this Vertical LinearLayout, what confused me is, as per Google's API, I tried to call setWidth(20) on button before adding it in ViewGroup, but Button occupied width 'match_parent' rather than 20dp.

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="fill_parent"
    android:layout_margin="10dp"
    android:orientation="vertical"
    android:id="@+id/first_layout">
    </LinearLayout>

//Inside onCreate() of activity..    
    LinearLayout firstLayout = (LinearLayout) findViewById(R.id.first_layout);
            Button button = new Button(this);
            button.setText(R.string.click_on_me);
            button.setWidth(20);
            firstLayout.addView(button);

CASE 2:on setting layout_width of LinearLayout to 'wrap_content', and calling setWidth(20), It now considered given explicit width value i.e 20dp.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:layout_margin="10dp"
    android:orientation="vertical"
    android:id="@+id/first_layout">
</LinearLayout>

//Inside onCreate() method
LinearLayout firstLayout = (LinearLayout) findViewById(R.id.first_layout);
        Button button = new Button(this);
        button.setText(R.string.click_on_me);
        button.setWidth(20);//In this case, its working
        firstLayout.addView(button);

CASE 3: Finally, removing my custom call to setWidth(20), Button acquired width as 'wrap_content'.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:layout_margin="10dp"
    android:orientation="vertical"
    android:id="@+id/first_layout">

</LinearLayout>

//Inside onCreate() method.
LinearLayout firstLayout = (LinearLayout) findViewById(R.id.first_layout);
        Button button = new Button(this);
        button.setText(R.string.click_on_me);        
        firstLayout.addView(button);

Ques : So it is clear by case-2, that using LayoutParams is not necessary, if I wish to explicitly use setWidth() method.Then In Case 4: i.e LinearLayout's width set as 'match_parent' and button.setWidth(20) is also called. But why Button is still not taking explicitly given width value, again output is exactly same as CASE 1.

Thanks in advance.

Answer 1

You need to define an appropriate LayoutParams for your button view. Then add it to your firstLayout.

LayoutParams params = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
params.height = XX;
params.width = XX;
button.setLayoutParams(params);