Android margin between buttons in grid layout

Question

I'm trying to create a grid layout containing buttons but by default there is a space between these buttons and I don't need that. The .xml file looks like this:

<?xml version="1.0" encoding="utf-8"?>
<ScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_gravity="center">
    <HorizontalScrollView android:id="@+id/HorizontalScrollView"
                          android:layout_width="wrap_content"
                          android:layout_height="wrap_content"
                          android:layout_gravity="center">
    <GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:id="@+id/gridLayout"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center">
    </GridLayout>
  </HorizontalScrollView>
</ScrollView>

The code where I create the buttons and add it to the grid layout:

for (int rowCounter = 0; rowCounter < DIMENSION; rowCounter++)
    for (int columnCounter = 0; columnCounter < DIMENSION; columnCounter++) {
        Button b = new Button(this);
        b.setText(" ");
        GridLayout.LayoutParams params = new GridLayout.LayoutParams();
        params.setMargins(0, 0, 0, 0);
        b.setLayoutParams(params);
        gridLayout.addView(b);
    }

Here is an image of how it looks:

Answer 1

Android default button have some padding.
If you don't want that space, you need create a custom backgroud for your buttons.

This is an example:

button_dark_gradient.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
    <item android:state_pressed="true" >
         <shape>
            <gradient
                android:startColor="#00000000"
                android:centerColor="#FFFFFF"
                android:endColor="#00000000"
                android:angle="270" />
            <padding
                android:left="10dp"
                android:top="10dp"
                android:right="10dp"
                android:bottom="10dp" />          
        </shape>

        <shape>
            <gradient
                android:startColor="#00CFCCCE"
                android:centerColor="#FFFFFF"
                android:endColor="#00BAB8B9"
                android:angle="270" />
            <padding
                android:left="10dp"
                android:top="10dp"
                android:right="10dp"
                android:bottom="10dp" />            
        </shape>        
    </item>
    <item>
        <shape>
            <gradient
                android:startColor="#00CFCCCE"
                android:centerColor="#FFFFFF"
                android:endColor="#00BAB8B9"
                android:angle="270" />
        </shape>
    </item>

</selector>  

Set the backgroud of your buttons to this drawable.

b.setBackground(getResources().getDrawable(R.drawable.button_dark_gradient));