[android] Android Layout Right Align

I have the following layout in place

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <LinearLayout android:orientation="vertical"
        android:layout_width="fill_parent" android:layout_height="fill_parent"
        android:layout_weight="1">


        <WebView xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/webview" android:layout_width="fill_parent"
            android:layout_height="fill_parent" />
    </LinearLayout>

    <LinearLayout android:orientation="horizontal"  android:layout_width="fill_parent" android:layout_height="fill_parent"  android:layout_weight="13">
        <LinearLayout android:id="@+id/LinearLayout01" android:layout_width="wrap_content" android:layout_height="wrap_content">
            <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1">
                    <ImageButton android:background="@null" android:id="@+id/back" android:layout_width="fill_parent" android:layout_height="wrap_content" android:src="@drawable/back" android:padding="10dip" />
            </LinearLayout>

            <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1">
                <ImageButton android:background="@null" android:id="@+id/forward" android:layout_width="fill_parent" android:layout_height="wrap_content" android:src="@drawable/forward" android:padding="10dip" />
            </LinearLayout>

        </LinearLayout>

        <RelativeLayout android:orientation="horizontal" android:layout_width="wrap_content" android:layout_height="fill_parent"    android:layout_weight="1" >
                <ImageButton android:background="@null" android:id="@+id/special"   android:layout_width="fill_parent" android:layout_height="wrap_content" android:src="@drawable/barcode" android:padding="10dip" android:layout_gravity="right"/>
        </RelativeLayout>




    </LinearLayout>


</LinearLayout>

For the purpose of this question, I am only concerned about the lower half of the layout. Right now it contains 3 imagebuttons. The first 2, I want right next to each other left aligned. The third one, I want to be aligned to the right side.

As is, the first 2 buttons are where I want them to be, but the 3rd is stubbernly staying left-aligned. How would I make it right aligned.

If you want to use LinearLayout, you can do alignment with layout_weight with Space element.

E.g. following layout places textView and textView2 next to each other and textView3 will be right-aligned

<LinearLayout
    android:orientation="horizontal"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView2" />

    <Space
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="20dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView3" />
</LinearLayout>

you can achieve the same effect without Space if you would set layout_weight to textView2. It's just that I like things more separated, plus to demonstrate Space element.

    <TextView
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Medium Text"
        android:id="@+id/textView2" />

Note that you should (not must though) set layout_width explicitly as it will be recalculated according to it's weight anyway (same way you should set height in elements of vertical LinearLayout). For other layout performance tips see Android Layout Tricks series.

You can do all that by using just one RelativeLayout (which, btw, don't need android:orientation parameter). So, instead of having a LinearLayout, containing a bunch of stuff, you can do something like:

<RelativeLayout>
    <ImageButton
        android:layout_width="wrap_content"
        android:id="@+id/the_first_one"
        android:layout_alignParentLeft="true"/>
    <ImageButton
        android:layout_width="wrap_content"
        android:layout_toRightOf="@+id/the_first_one"/>
    <ImageButton
        android:layout_width="wrap_content"
        android:layout_alignParentRight="true"/>
</RelativeLayout>

As you noticed, there are some XML parameters missing. I was just showing the basic parameters you had to put. You can complete the rest.

To support older version Space can be replaced with View as below. Add this view between after left most component and before right most component. This view with weight=1 will stretch and fill the space

    <View
        android:layout_width="0dp"
        android:layout_height="20dp"
        android:layout_weight="1" />

Complete sample code is given here. It has has 4 components. Two arrows will be on the right and left side. The Text and Spinner will be in the middle.

    <ImageButton
        android:id="@+id/btnGenesis"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center|center_vertical"
        android:layout_marginBottom="2dp"
        android:layout_marginLeft="0dp"
        android:layout_marginTop="2dp"
        android:background="@null"
        android:gravity="left"
        android:src="@drawable/prev" />

    <View
        android:layout_width="0dp"
        android:layout_height="20dp"
        android:layout_weight="1" />

    <TextView
        android:id="@+id/lblVerseHeading"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:gravity="center"
        android:textSize="25sp" />

    <Spinner
        android:id="@+id/spinnerVerses"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="5dp"
        android:gravity="center"
        android:textSize="25sp" />

    <View
        android:layout_width="0dp"
        android:layout_height="20dp"
        android:layout_weight="1" />

    <ImageButton
        android:id="@+id/btnExodus"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center|center_vertical"
        android:layout_marginBottom="2dp"
        android:layout_marginLeft="0dp"
        android:layout_marginTop="2dp"
        android:background="@null"
        android:gravity="right"
        android:src="@drawable/next" />
</LinearLayout>

This is an example for a RelativeLayout:

RelativeLayout relativeLayout=(RelativeLayout)vi.findViewById(R.id.RelativeLayoutLeft);
                RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams)relativeLayout.getLayoutParams();
                params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
                relativeLayout.setLayoutParams(params);

With another kind of layout (example LinearLayout) you just simply has to change RelativeLayout for LinearLayout.