import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;public class CrossView extends View {private float mRotation;private Paint mPaint;public CrossView( Context context, AttributeSet attrs ) {//AttributeSet对象在实例化时被系统传给了视图super( context, attrs );//start 创建paint对象mPaint = new Paint();mPaint.setAntiAlias( true );mPaint.setColor( 0xFFFFFFFF );//end 创建paint对象//使用obtainStyledAttributes方法来创建一个TypedArray，这是访问存储于AttributeSet中的值的一个方便类，这类执行内部缓存，//所以当你结束使用它之后随时调用回收函数。注意：需同时使用<declare-styleable>名称和<arr>名称的访问自定义属性TypedArray arr = getContext().obtainStyledAttributes( attrs,R.styleable.cross );int color = arr.getColor( R.styleable.cross_android_color, Color.WHITE );float rotation = arr.getFloat( R.styleable.cross_rotation, 0f );//remember to call this when finishedarr.recycle();setColor(color);setRotation(rotation);}private void setRotation( float rotation ) {// TODO Auto-generated method stubmRotation = rotation;}private void setColor( int color ) {// TODO Auto-generated method stubmPaint.setColor( color );}//重写onMeasure方法@Overrideprotected void onMeasure( int widthMeasureSpec, int heightMeasureSpec ) {// TODO Auto-generated method stubsuper.onMeasure( widthMeasureSpec, heightMeasureSpec );//需要使用计算好的宽和高的值作为该方法的实参setMeasuredDimension( calculateMeasure(widthMeasureSpec), calculateMeasure(heightMeasureSpec) );}float[] mPoints = {0.5f,0f,0.5f,1f,0f,0.5f,1f,0.5f};@Overrideprotected void onDraw( Canvas canvas ) {// TODO Auto-generated method stubsuper.onDraw( canvas );canvas.save();//所有的在画布上绘图的调用都应当受对应的sava（）和restore（）的约束int scale = getWidth();canvas.scale( scale, scale );canvas.rotate( mRotation );canvas.drawLines( mPoints, mPaint );//绘制十字的两条线canvas.restore();//所有的在画布上绘图的调用都应当受对应的sava（）和restore（）的约束}private static final int DEFAULT_SIZE = 100;//默认的试图尺寸//实现计算测量值的代码private int calculateMeasure(int measureSpec){int result = ( int ) ( DEFAULT_SIZE*getResources().getDisplayMetrics().density );int specMode = MeasureSpec.getMode( measureSpec );//在MeasureSpec中检索模式int specSize = MeasureSpec.getSize( measureSpec );//在MeasureSpec中检索尺寸//基于模式选择尺寸if(specMode == MeasureSpec.EXACTLY){result = specSize;}else if(specMode == MeasureSpec.AT_MOST){result = Math.min( result, specSize );}return result;}
}
（二）自定义属性<?xml version="1.0" encoding="utf-8"?>
<!-- 该文件被放置在res/values/目录下 -->
<resources><!-- 声明属性 --><declare-styleable name="cross"><attr name="android:color"/><attr name="rotation" format="string"/></declare-styleable><!-- <attr name="test" format="string"/><declare-styleable name="foo"><attr name="test"/></declare-styleable><declare-styleable name="bar"><attr name="test"/></declare-styleable> -->
</resources>
（三）在XML中使用自定义View
<?xml version="1.0" encoding="utf-8"?><!-- 要使用在XML中的自定义属性，首先必须为视图声明命名空间 -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:example="http://schemas.android.com/apk/res/com.example"android:orientation="vertical"android:layout_width="fill_parent"android:layout_height="fill_parent"><!-- 添加CrossView --><com.example.CrossViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"/><com.example.CrossViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"example.rotation="30" android:color="#0000FF"/>/><com.example.CrossViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"example.rotation="40" android:color="#FFFF00"/>
</LinearLayout>