Android自定義Shape 加上陰影shadow之方法

Android支持自定義Shape， 以畫出需要的形狀，可以作為TextView, EditText, Button的背景drawable資源。Shape很簡單，就是一個XML文件，SDK文檔里描述其格式如下：

1. xml version="1.0" encoding="utf-8"?>  
2. <shape  
3.     xmlns:Android="http://schemas.android.com/apk/res/android"  
4.     Android:shape=["rectangle" | "oval" | "line" | "ring"] >  
5.     <corners  
6.         Android:radius="integer"  
7.         Android:topLeftRadius="integer"  
8.         Android:topRightRadius="integer"  
9.         Android:bottomLeftRadius="integer"  
10.         Android:bottomRightRadius="integer" />  
11.     <gradient  
12.         Android:angle="integer"  
13.         Android:centerX="integer"  
14.         Android:centerY="integer"  
15.         Android:centerColor="integer"  
16.         Android:endColor="color"  
17.         Android:gradientRadius="integer"  
18.         Android:startColor="color"  
19.         Android:type=["linear" | "radial" | "sweep"]   
20.         Android:usesLevel=["true" | "false"] />  
21.     <padding  
22.         Android:left="integer"  
23.         Android:top="integer"  
24.         Android:right="integer"  
25.         Android:bottom="integer" />  
26.     <size  
27.         Android:width="integer"  
28.         Android:height="integer" />  
29.     <solid  
30.         Android:color="color" />  
31.     <stroke  
32.         Android:width="integer"  
33.         Android:color="color"  
34.         Android:dashWidth="integer"  
35.         Android:dashGap="integer" />  
36. shape>  

其支持的屬性沒有shadow， 做Web前端開發的同學寫CSS可以很方便地加一個shadow屬性值，如何給Android Shape加一個shadow，以得到類似的效果呢？

答案是使用layer-list !   直接上代碼如下：

1. xml version="1.0" encoding="utf-8"?>  
2. <layer-list xmlns:Android="http://schemas.android.com/apk/res/android">  
3.   
4.     <item>  
5.         <shape Android:shape="rectangle">  
6.             <solid Android:color="#792a03" />  
7.             <corners Android:radius="19dp" />  
8.         shape>  
9.     item>  
10.        
11.     <item  Android:top="1px">  
12.         <shape Android:shape="rectangle">  
13.             <gradient Android:startColor="#ffdb8f" android:endColor="#ffdb8f"  
14.                 Android:angle="270" />  
15.             <padding Android:left="5dp" android:top="3dp" android:right="5dp"  
16.                 Android:bottom="3dp" />  
17.             <corners Android:radius="20dp" />  
18.         shape>  
19.   
20.     item>  
21.   
22.  layer-list>  

將以上xml存成btn_test, 放到res/drawable/目錄下。 將該drawable xml設為一個TextView的backgroiund,

1. <TextView  
2.        Android:background="@drawable/btn_test"  
3.   
4.         Android:layout_marginTop="20dip"  
5.         Android:layout_marginLeft="5dip"  
6.     Android:textColor="#792a03"            
7.            
8.         Android:text="1天2小時14分20秒"  
9.        Android:layout_width="wrap_content"    
10.        Android:layout_height="wrap_content" />  

其效果如下圖所示： 

關於layer-list的進一步解釋見SDK文檔，如下： 

Layer List

A LayerDrawable is a drawable object that manages an array of other drawables. Each drawable in the list is drawn in the order of the list—the last drawable in the list is drawn on top.

Each drawable is represented by an element inside a single element.

file location:

res/drawable/filename .xml
The filename is used as the resource ID.

compiled resource datatype:

Resource pointer to a LayerDrawable .

resource reference:

In Java: R.drawable.filename
In XML: @[package :]drawable/filename

syntax:

            ="http://schemas.android.com/apk/res/android" >              

elements:

Required. This must be the root element. Contains one or more elements.

attributes:

xmlns:Android

String . Required. Defines the XML namespace, which must be "http://schemas.android.com/apk/res/android" .

Defines a drawable to place in the layer drawable, in a position defined by its attributes. Must be a child of a element. Accepts child elements.

attributes:

Android:drawable

Drawable resource . Required . Reference to a drawable resource.

android:id

Resource ID . A unique resource ID for this drawable. To create a new resource ID for this item, use the form: "@+id/name " . The plus symbol indicates that this should be created as a new ID. You can use this identifier to retrieve and modify the drawable with View.findViewById() or Activity.findViewById() .

android:top

Integer . The top offset in pixels.

android:right

Integer . The right offset in pixels.

android:bottom

Integer . The bottom offset in pixels.

android:left

Integer . The left offset in pixels.

All drawable items are scaled to fit the size of the containing View, by default. Thus, placing your images in a layer list at different positions might increase the size of the View and some images scale as appropriate. To avoid scaling items in the list, use a element inside the element to specify the drawable and define the gravity to something that does not scale, such as "center" . For example, the following defines an item that scales to fit its container View: