android相对布局实例—登录界面

<RelativeLayout 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:layout_margin="20dp"    tools:context=".MainActivity" >        <TextView         android:id="@+id/Txttitle"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentLeft="true"        android:gravity="center_horizontal"        android:layout_alignParentRight="true"        android:text="登录界面"/>    <EditText        android:id="@+id/username"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignLeft="@id/Txttitle"        android:layout_alignRight="@id/Txttitle"        android:layout_below="@id/Txttitle"         android:layout_marginTop="20dp"        android:hint="username"/>    <EditText         android:id="@+id/password"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_below="@id/username"        android:layout_alignLeft="@id/username"        android:layout_alignRight="@id/username"         android:layout_marginTop="20dp"        android:hint="password"        android:inputType="textCapWords"/></RelativeLayout>