第五篇--自定义View

View的基类是一个100乘以100的空白正方形，要改变它，就需要重写onMeasure和onDraw方法。

写一个《android高级编程第三版》中的例子，自定义一个罗盘view:

        CompassView.java

package com.godlovesoccer.blogcustomview;import android.content.Context;import android.content.res.Resources;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.util.AttributeSet;import android.view.KeyEvent;import android.view.MotionEvent;import android.view.View;import android.view.accessibility.AccessibilityEvent;public class CompassView extends View{private float bearing;private Paint markerPaint;private Paint textPaint;private Paint circlePaint;private String northString;private String southString;private String westString;private String eastString;private int textHeight;public void setBearing(float _bearing){bearing=_bearing;sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_TEXT_CHANGED);}public float getBearing(){return bearing;}public CompassView(Context context){super(context);initCompassView();}public CompassView(Context context,AttributeSet attrs,int defaultStyle){super(context,attrs,defaultStyle);initCompassView();}public CompassView(Context context,AttributeSet attrs){super(context,attrs);initCompassView();}protected void initCompassView(){setFocusable(true);Resources r=this.getResources();circlePaint=new Paint(Paint.ANTI_ALIAS_FLAG);circlePaint.setStrokeWidth(1);circlePaint.setStyle(Paint.Style.FILL_AND_STROKE);northString=r.getString(R.string.cardinal_north);southString=r.getString(R.string.cardinal_south);eastString=r.getString(R.string.cardinal_east);westString=r.getString(R.string.cardinal_west);textPaint=new Paint(Paint.ANTI_ALIAS_FLAG);textPaint.setColor(r.getColor(R.color.text_color));textHeight=(int)textPaint.measureText("yY");markerPaint=new Paint(Paint.ANTI_ALIAS_FLAG);markerPaint.setColor(r.getColor(R.color.marker_color));}protected void onMeasure(int wMeasureSpec,int hMeasureSpec){int measuredHeight=measure(hMeasureSpec);int measuredWidth=measure(wMeasureSpec);int d=Math.min(hMeasureSpec,wMeasureSpec);setMeasuredDimension(d,d);}private int measure(int measureSpec){int result=0;int specMode=MeasureSpec.getMode(measureSpec);int specSize=MeasureSpec.getSize(measureSpec);if(specMode==MeasureSpec.UNSPECIFIED){result=200;}else// if(specMode==MeasureSpec.EXACTLY){result=specSize;}return result;}protected void onDraw(Canvas canvas){int height=getMeasuredHeight();int width=getMeasuredWidth();int px=width/2;int py=height/2;int radius=Math.min(px, py);canvas.drawCircle(px, py, radius, circlePaint);canvas.save();int textWidth=(int)textPaint.measureText("W");int cardinalX=px-textWidth/2;int cardinalY=py-radius+textHeight;for(int i=0;i<24;i++){canvas.drawLine(px, py-radius, px, py-radius+10, markerPaint);canvas.save();canvas.translate(0, textHeight);if(i%6==0){String dirString="";switch(i){case 0:{dirString=northString;int arrowY=2*textHeight;canvas.drawLine(px, arrowY, px-5, 3*textHeight, markerPaint);canvas.drawLine(px, arrowY, px+5, 3*textHeight, markerPaint);break;}case 6:dirString=eastString;break;case 12:dirString=southString;break;case 18:dirString=westString;break;}canvas.drawText(dirString, cardinalX, cardinalY, textPaint);}else if(i%3==0){String angle=String.valueOf(i*15);float angleTextWidth=textPaint.measureText(angle);int angleTextX=(int)(px-angleTextWidth/2);int angleTextY=py-radius+textHeight;canvas.drawText(angle, angleTextX, angleTextY, textPaint);}canvas.restore();canvas.rotate(15,px,py);}canvas.restore();}}