Mysterious padding on the left side of the Android Toolbar.

I was troubled by a mysterious issue where a gap appeared, even though neither margin nor padding was applied to the RelativeLayout inside the Toolbar.

The RelativeLayout is set to match_parent, and the parent element doesn’t have any properties that would create a gap, so why is this happening?

Here’s how the XML looks.

<android.support.v7.widget.Toolbar
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways" >
            <RelativeLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent" >
                <ImageView
                    android:id="@+id/home_bt"
                    android:layout_width="30dp"
                    android:layout_height="30dp"
                    android:layout_alignParentLeft="true"
                    android:background="@drawable/icon_home"/>
                <ImageView
                    android:id="@+id/folder_plus"
                    android:layout_width="35dp"
                    android:layout_height="35dp"
                    android:layout_alignParentRight="true"
                    android:background="@drawable/icon_folder_plus"/>
            </RelativeLayout>
</android.support.v7.widget.Toolbar>

There is a mysterious padding on the left side of the HOME button (ImageView @+id/home_bt).
Of course, no margin is specified in the parent element.

Solution

Resolved by adding the contentInsetStart attribute to the Toolbar and setting the padding to “0”.

<android.support.v7.widget.Toolbar
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            <!-- Add the contentInsetStart element. -->
            app:contentInsetStart="0dp"
            app:layout_scrollFlags="scroll|enterAlways" >
            <RelativeLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent" >
                <ImageView
                    android:id="@+id/home_bt"
                    android:layout_width="30dp"
                    android:layout_height="30dp"
                    android:layout_alignParentLeft="true"
                    android:background="@drawable/icon_home"/>
                <ImageView
                    android:id="@+id/folder_plus"
                    android:layout_width="35dp"
                    android:layout_height="35dp"
                    android:layout_alignParentRight="true"
                    android:background="@drawable/icon_folder_plus"/>
            </RelativeLayout>
</android.support.v7.widget.Toolbar>

It seems like a margin is added by default.
I got stuck on this one for a while…