Eclipse 开发 Android, RelativeLayout （学习3）

Hello, RelativeLayout

A RelativeLayout is a ViewGroup that allows you to layout child elements in positions relative to the parent or siblings elements.

1. Start a new project/Activity called HelloRelativeLayout.
2. Open the layout file. Make it like so:

   <?xml version="1.0" encoding="utf-8"?>
   <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="fill_parent"
       android:layout_height="fill_parent">
   
       <TextView
           android:id="@+id/label"
           android:layout_width="fill_parent"
           android:layout_height="wrap_content"
           android:text="Type here:"/>
   
       <EditText
           android:id="@+id/entry"
           android:layout_width="fill_parent"
           android:layout_height="wrap_content"
           android:background="@android:drawable/editbox_background"
           android:layout_below="@id/label"/>
   
       <Button
           android:id="@+id/ok"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_below="@id/entry"
           android:layout_alignParentRight="true"
           android:layout_marginLeft="10dip"
           android:text="OK" />
   
       <Button
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_toLeftOf="@id/ok"
           android:layout_alignTop="@id/ok"
           android:text="Cancel" />
   
   </RelativeLayout>
   

   Pay attention to each of the additional layout_* attributes (besides the usual width and height, which are required for all elements). When using relative layout, we use attributes like layout_below and layout_toLeftOf to describe how we'd like to position each View. Naturally, these are different relative positions, and the value of the attribute is the id of the element we want the position relative to.

3. Make sure your Activity loads this layout in the onCreate() method:

    

   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
   }
   

   R.layout.main refers to the main.xml layout file.

4. Run it.

You should see the following:

备注：RelativeLayout  这种布局方式，是靠一些组件关联，然后形成UI界面。