Android应用开发学习之相对布局

作者：刘昊昱

博客：http://blog.csdn.net/liuhaoyutz

相对布局RelativeLayout是指按照组件之间的相对位置进行布局，如一个组件在另一个组件的左边、右边、上边或下边等。

RelativeLayout常用的XML属性有：

android:gravity

用于设置布局管理器中各子组件的对齐方式。

android:ignoreGravity

用于指定哪个组件不受gravity属性的影响。

在相对布局管理器中，如果只有上面两个属性是远远不够的，为了更好地控制该布局管理器中的组件，RelativeLayout提供了一个内部类：RelativeLayout.LayoutParams，通过该类提供的大量XML属性，可以很好的控制RelativeLayout中的各组件的布局。

下表是Android官方网站上给出的RelativeLayout.LayoutParams的XML属性

Attribute Name	Description
android:layout_above	Positions the bottom edge of this view above the given anchor view ID.
android:layout_alignBaseline	Positions the baseline of this view on the baseline of the given anchor view ID.
android:layout_alignBottom	Makes the bottom edge of this view match the bottom edge of the given anchor view ID.
android:layout_alignEnd	Makes the end edge of this view match the end edge of the given anchor view ID.
android:layout_alignLeft	Makes the left edge of this view match the left edge of the given anchor view ID.
android:layout_alignParentBottom	If true, makes the bottom edge of this view match the bottom edge of the parent.
android:layout_alignParentEnd	If true, makes the end edge of this view match the end edge of the parent.
android:layout_alignParentLeft	If true, makes the left edge of this view match the left edge of the parent.
android:layout_alignParentRight	If true, makes the right edge of this view match the right edge of the parent.
android:layout_alignParentStart	If true, makes the start edge of this view match the start edge of the parent.
android:layout_alignParentTop	If true, makes the top edge of this view match the top edge of the parent.
android:layout_alignRight	Makes the right edge of this view match the right edge of the given anchor view ID.
android:layout_alignStart	Makes the start edge of this view match the start edge of the given anchor view ID.
android:layout_alignTop	Makes the top edge of this view match the top edge of the given anchor view ID.
android:layout_alignWithParentIfMissing	If set to true, the parent will be used as the anchor when the anchor cannot be be found for layout_toLeftOf, layout_toRightOf, etc.
android:layout_below	Positions the top edge of this view below the given anchor view ID.
android:layout_centerHorizontal	If true, centers this child horizontally within its parent.
android:layout_centerInParent	If true, centers this child horizontally and vertically within its parent.
android:layout_centerVertical	If true, centers this child vertically within its parent.
android:layout_toEndOf	Positions the start edge of this view to the end of the given anchor view ID.
android:layout_toLeftOf	Positions the right edge of this view to the left of the given anchor view ID.
android:layout_toRightOf	Positions the left edge of this view to the right of the given anchor view ID.
android:layout_toStartOf	Positions the end edge of this view to the start of the given anchor view ID.

下面我们来看一个例子，该程序运行效果如图所示：

我们来看该程序的主布局文件main.xml：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
 	android:id="@+id/relativeLayout1"
 	android:layout_width="fill_parent"
	android:layout_height="fill_parent"
	xmlns:android="http://schemas.android.com/apk/res/android"
 >
 	<!-- 添加一个居中显示的文本视图textView1 -->
    <TextView android:text="您正在学习RelativeLayout的用法 ，是否开始动手练习？"
     android:id="@+id/textView1"
     android:textSize="24px"
     android:layout_height="wrap_content"
     android:layout_width="wrap_content"
     android:layout_centerInParent="true"
	/>
	<!-- 添加一个在button2左侧显示的按钮button1 -->
    <Button
     android:text="开始练习"
     android:id="@+id/button1"
     android:layout_height="wrap_content"
     android:layout_width="wrap_content"
     android:layout_below="@+id/textView1"
     android:layout_toLeftOf="@+id/button2"
     />
     <!-- 添加一个按钮button2，该按钮与textView1的右边界对齐 -->
    <Button
     android:text="不练习"
     android:id="@+id/button2"
     android:layout_height="wrap_content"
     android:layout_width="wrap_content"
     android:layout_alignRight="@+id/textView1"
     android:layout_below="@+id/textView1"
	/>
 </RelativeLayout>

通过这个例子，我们可以理解相对布局控件RelativeLayout的用法了。