如何在屏幕底部对齐这些按钮？

Question

This is the UI I'm working on:

I'm trying to get the buttons at the bottom to be anchored to the bottom of the screen but in order to do this, It seems I need to have a hard-coded height for the

<LinearLayout>
    <GridLayout></GridLayout>
    <GridLayout></GridLayout>
</LinearLayout>

What we see in the image is 305dip . If I increase that to eg 335dip it's aligned with the bottom correctly, but I know this isn't right. However, if I set the LinearLayout 's height to match_parent , eg

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"

it pushes the buttons in the red box right off the bottom of the screen.

I need a way for the keypad to fill exactly as much space as it needs to, and keep the correct buttons anchored at the bottom of the screen at all times. How can I do this?

This is my layout definition:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffff"
    tools:context=".FullscreenActivity"
    android:orientation="vertical"
    android:paddingTop="0dip"
    android:paddingBottom="0dip">
    <TextView
        android:id="@+id/keypadOutput"
        android:layout_width="match_parent"
        android:layout_height="70dip"
        android:gravity="center_vertical"
        android:keepScreenOn="true"
        android:text="@string/dummy_content"
        android:textColor="#000000"
        android:textSize="25sp"
        android:textStyle="bold"
        android:background="@drawable/LCD"
        android:paddingLeft="15dip"
        android:layout_margin="5dip" />
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="305dip"
        android:orientation="horizontal">
        <GridLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:columnCount="3"
            android:orientation="horizontal">
            <!-- 12 buttons -->
        </GridLayout>
        <GridLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:columnCount="1"
            android:orientation="horizontal">
            <!-- 3 buttons -->
        </GridLayout>
    </LinearLayout>
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:gravity="bottom|center_horizontal"
        android:orientation="horizontal">
        <!-- 3 image buttons -->
    </LinearLayout>
</LinearLayout>

Correct Answer

as per @Ascorbin's answer below, this was the solution:

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:gravity="center_horizontal">
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="center_horizontal"
        android:layout_alignParentBottom="true">
        <ImageButton
            android:id="@+id/button_keypad"
            android:layout_width="45dip"
            android:layout_height="45dip"
            android:background="@drawable/navigation_button"
            android:src="@drawable/keypad_light" />
        <ImageButton
            android:id="@+id/button_unset"
            android:layout_width="45dip"
            android:layout_height="45dip"
            android:background="@drawable/navigation_button"
            android:src="@drawable/unset_light" />
        <ImageButton
            android:id="@+id/button_logs"
            android:layout_width="45dip"
            android:layout_height="45dip"
            android:background="@drawable/navigation_button"
            android:src="@drawable/logs_light" />
    </LinearLayout>
</RelativeLayout>

Answer 1

I would suggest you to change

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="305dip"
    android:orientation="horizontal">

to

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:orientation="horizontal">

Answer 2

you can add margin from top whatever you want

<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom"
    android:gravity="bottom|center_horizontal"
    android:layout_marginTop="50dp"
    android:orientation="horizontal">
    <!-- 3 image buttons -->
</LinearLayout>

Answer 3

I don't think you do yourself a favor by hardvoding layout heights. I'd suggest to wrap your whole layout in a RelativeLayout and anchor your buttons to the bottom with alighParentBottom="true" .