Android之AttributeSet案例详解

public interface AttributeSet {
    /**
     * Returns the number of attributes available in the set.
     * 
     * @return A positive integer, or 0 if the set is empty.
     */
    public int getAttributeCount();

    /**
     * Returns the name of the specified attribute.
     * 
     * @param index Index of the desired attribute, 0...count-1.
     * 
     * @return A String containing the name of the attribute, or null if the
     *         attribute cannot be found.
     */
    public String getAttributeName(int index);

    /**
     * Returns the value of the specified attribute as a string representation.
     * 
     * @param index Index of the desired attribute, 0...count-1.
     * 
     * @return A String containing the value of the attribute, or null if the
     *         attribute cannot be found.
     */
    public String getAttributeValue(int index);

    /**
     * Returns the value of the specified attribute as a string representation.
     * The lookup is performed using the attribute name.
     * 
     * @param namespace The namespace of the attribute to get the value from.
     * @param name The name of the attribute to get the value from.
     * 
     * @return A String containing the value of the attribute, or null if the
     *         attribute cannot be found.
     */
    public String getAttributeValue(String namespace, String name);

查看AttributeSet的源码 你会发现它是一个接口 是个什么接口呢?

熟悉XML解析的人知道 在XML解析中是有AttributeSet这个东西的,XML解析根据节点取出节点相对应的数据。

Android中,我们写的布局文件就是XML形式的,所以这就是每次我们自定义View的时候,构造方法有AttributeSet的原因。

SDK给出的解释如下:

A collection of attributes, as found associated with a tag in an XML document. Often you will not want to use this interface directly, instead passing it to Resources.Theme.obtainStyledAttributes() which will take care of parsing the attributes for you. In particular, the Resources API will convert resource references (attribute values such as "@string/my_label" in the original XML) to the desired type for you; if you use AttributeSet directly then you will need to manually check for resource references (with getAttributeResourceValue(int, int)) and do the resource lookup yourself if needed. Direct use of AttributeSet also prevents the application of themes and styles when retrieving attribute values.

This interface provides an efficient mechanism for retrieving data from compiled XML files, which can be retrieved for a particular XmlPullParser through Xml.asAttributeSet(). Normally this will return an implementation of the interface that works on top of a generic XmlPullParser, however it is more useful in conjunction with compiled XML resources:

那我们自定义View的时候,AttributeSet又是怎么用的呢?

一般情况下,我们是在values下面新建一个attrs文件夹

<declare-styleable name="MyView">  
        <attr name="textColor" format="color"/>  
        <attr name="textSize" format="dimension"/>  
    </declare-styleable>

布局文件如下:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:myapp="http://schemas.android.com/apk/res/com.example.androidtest"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:background="@android:color/black"
    android:layout_height="match_parent">
    
    <com.example.androidtest.MyView
        android:layout_width="fill_parent"  
        android:layout_height="wrap_content"    
        myapp:textColor="#FFFFFFFF"    
        myapp:textSize="62dp"  
        ></com.example.androidtest.MyView>

</LinearLayout>

自定义View样例代码:

public class MyView extends TextView {

    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
        
        TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.MyView);
        int textColor = array.getColor(R.styleable.MyView_textColor, 0XFF00FF00);
        float textSize = array.getDimension(R.styleable.MyView_textSize, 36);
        setTextColor(textColor);
        setTextSize(textSize);
        setText("22222222222");
        
        array.recycle();
    }

    public MyView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }
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