使用android:layout_weight解决布局时把按纽压到屏幕外的问题

<? 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"
    android:orientation ="vertical"   >

     < Gallery 
         android:id ="@+id/gallery"
        android:layout_width ="fill_parent"
        android:layout_height ="70px"
         />
    
     < GridView 
            android:id ="@+id/gridview"     
           android:layout_width ="fill_parent"      
           android:layout_height ="fill_parent"    
           android:columnWidth ="90px"    
           android:numColumns ="auto_fit"     
           android:verticalSpacing ="2dp"     
           android:horizontalSpacing ="2dp"    
           android:stretchMode ="columnWidth"     
           android:gravity ="center"
           
           android:layout_below ="@id/gallery"
            />
    
     < LinearLayout
         android:id ="@+id/linesexshow"
        android:layout_width ="fill_parent"
           android:layout_height ="fill_parent"
           android:layout_below ="@id/gallery"
           android:orientation ="vertical"
           android:visibility ="gone"
         >
        
         < ImageView 
             android:id ="@+id/ivsexshow"
            android:layout_width ="fill_parent"      
            android:layout_height ="0dp"  
            android:layout_centerHorizontal ="true"
            android:visibility ="gone"
            android:scaleType ="fitCenter"
            android:layout_weight ="100"
             />
         < Button 
             android:id ="@+id/btnback"
            android:layout_width ="fill_parent"
            android:layout_height ="wrap_content"
            android:text ="@string/btnback"
            android:visibility ="gone"
            android:layout_centerHorizontal ="true"
            android:layout_weight ="1"
             />
        
        
     </ LinearLayout >
</ RelativeLayout >