如何自定义View及在配置文件中增加描述属性

自定义View的类必须继承自View并且重写onDraw(Canvas canvas)方法；
增加自定义的属性描述必须在values中增加attrs.xml来描述View的属性；
例如：
<?xml version="1.0" encoding="UTF-8"?>
<resources>
    <declare-styleable name="ClockView">
        <attr name="clockColor" format="color" />
        <attr name="visible" format="boolean"/>
        <attr name="timeZone" format="dimension">
            <enum name="londan" value="0" />
            <enum name="beijing" value="8" />
            <enum name="newyork" value="20" />
        </attr>
    </declare-styleable>
</resources>
color，boolean，dimension，string为属性的数据类型；
在自定义的View中引用可以通过TypeArray来获取，例如；
TypedArray typedArray = context.obtainStyledAttributes(attrs,R.styleable.ClockView);
int clockColor = typedArray.getColor(R.styleable.ClockView_clockColor, Color.WHITE);
其中index的值为：R.styleable.组件名称_属性。
在layout中的布局文件为
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:joydao="http://schemas.android.com/apk/res/net.joydao.clock"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <net.joydao.clock.view.ClockView
        android:id="@+id/joydaoClock" android:layout_width="wrap_content"
        android:layout_height="wrap_content" joydao:clockColor="#ffffff"
        joydao:visible="false" joydao:timeZone="beijing" />

</LinearLayout>
下面给出完整的Clock例子：
ClockView.java

package net.joydao.clock.view;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

import net.joydao.clock.R;
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.util.DisplayMetrics;
import android.view.View;
import android.view.WindowManager;

public class ClockView extends View implements Runnable {
   
    private Paint colorCirclePaint;
    private Paint pointPaint;
    private Paint hourMarkPaint;
    private Paint minuteMarkPaint;
    private Paint secondNeedlePaint;
    private Paint minuteNeedlePaint;
    private Paint hourNeedlePaint;
    private Paint textPaint;
    private Paint timePaint;
    private float hourMarkLen;
    private float minuteMarkLen;
    private float clockCircle;
    private float radius;
    private float hourNeedleRadius;
    private float minuteNeedleRadius;
    private float secondNeedleRadius;
    private float cx;
    private float cy;
    private boolean running = false;
    private int mYear;
    private int mMonth;
    private int mDay;
    private int mHour;
    private int mMinute;
    private int mSecond;
    private int clockColor;
   
    public ClockView(Context context){
        this(context,null);
    }

    public ClockView(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray typedArray = context.obtainStyledAttributes(attrs,R.styleable.ClockView);
        clockColor = typedArray.getColor(R.styleable.ClockView_clockColor, Color.WHITE);
        typedArray.recycle();
        pointPaint = new Paint();
        pointPaint.setAntiAlias(true);
        pointPaint.setStyle(Paint.Style.STROKE);
       
        colorCirclePaint = new Paint();
        colorCirclePaint.setTextAlign(Paint.Align.CENTER);
        colorCirclePaint.setAntiAlias(true);
        colorCirclePaint.setStrokeWidth(clockCircle);
        colorCirclePaint.setStyle(Paint.Style.STROKE);
       
        hourMarkPaint = new Paint();
        hourMarkPaint.setTextAlign(Paint.Align.CENTER);
        hourMarkPaint.setAntiAlias(true);
        hourMarkPaint.setStyle(Paint.Style.STROKE);
       
        minuteMarkPaint = new Paint();
        minuteMarkPaint.setTextAlign(Paint.Align.CENTER);
        minuteMarkPaint.setAntiAlias(true);
        minuteMarkPaint.setStyle(Paint.Style.STROKE);
       
        secondNeedlePaint = new Paint();
        secondNeedlePaint.setTextAlign(Paint.Align.CENTER);
        secondNeedlePaint.setAntiAlias(true);
        secondNeedlePaint.setStyle(Paint.Style.STROKE);
       
        minuteNeedlePaint = new Paint();
        minuteNeedlePaint.setTextAlign(Paint.Align.CENTER);
        minuteNeedlePaint.setAntiAlias(true);
        minuteNeedlePaint.setStyle(Paint.Style.STROKE);
       
        hourNeedlePaint = new Paint();
        hourNeedlePaint.setTextAlign(Paint.Align.CENTER);
        hourNeedlePaint.setAntiAlias(true);
        hourNeedlePaint.setStyle(Paint.Style.STROKE);
       
        textPaint = new Paint();
        textPaint.setTextAlign(Paint.Align.CENTER);
        textPaint.setAntiAlias(true);
       
        timePaint = new Paint();
        timePaint.setTextAlign(Paint.Align.CENTER);
        timePaint.setAntiAlias(true);
        start();
    }
   
    public int getClockColor() {
        return clockColor;
    }

    public void setClockColor(int clockColor) {
        this.clockColor = clockColor;
        this.postInvalidate();
    }

    public void start(){
        running = true;
        new Thread(this).start();
    }
   
    public void stop(){
        running = false;
    }
   
    private void resetTime(){
        Calendar c = Calendar.getInstance(TimeZone.getDefault());
        c.setTime(new Date());
        mYear = c.get(Calendar.YEAR);
        mMonth = c.get(Calendar.MONTH)+1;
        mDay = c.get(Calendar.DAY_OF_MONTH);
        mHour = c.get(Calendar.HOUR_OF_DAY);
        mMinute = c.get(Calendar.MINUTE);
        mSecond = c.get(Calendar.SECOND);
    }
   
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        pointPaint.setColor(clockColor);
        colorCirclePaint.setColor(clockColor);
        hourMarkPaint.setColor(clockColor);
        minuteMarkPaint.setColor(clockColor);
        secondNeedlePaint.setColor(clockColor);
        minuteNeedlePaint.setColor(clockColor);
        hourNeedlePaint.setColor(clockColor);
        textPaint.setColor(clockColor);
        timePaint.setColor(clockColor);
        cx = getWidth()/2;
        cy = getHeight()/2;
        int tmp = getWidth()<=getHeight()?getWidth():getHeight();
        radius = tmp/2-2*clockCircle;
        hourMarkLen = radius/15;
        minuteMarkLen = radius/30;
        clockCircle = radius/60;
        pointPaint.setStrokeWidth(radius/25);
        textPaint.setTextSize(radius/8);
        timePaint.setTextSize(radius/5);
        hourMarkPaint.setStrokeWidth(radius/35);
        minuteMarkPaint.setStrokeWidth(radius/70);
        secondNeedlePaint.setStrokeWidth(radius/70);
        minuteNeedlePaint.setStrokeWidth(radius/35);
        hourNeedlePaint.setStrokeWidth(radius/20);
        hourNeedleRadius = radius - radius/2;
        minuteNeedleRadius = radius - radius/3;
        secondNeedleRadius = radius - radius/5;
        drawClockPanel(canvas,radius);
        drawNeedle(canvas);
        drawTime(canvas);
    }
   
    private void drawTime(Canvas canvas){
        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        DateFormat timeFormat = new SimpleDateFormat("hh:mm:ss a");
        String dateText = dateFormat.format(new Date());
        String timeText = timeFormat.format(new Date());
        float textX = cx;
        float timeY = cy+radius/2;
        float dateY = timeY+1.5f*textPaint.getTextSize();
        canvas.drawText(dateText, textX, dateY, textPaint);
        canvas.drawText(timeText, textX, timeY, timePaint);
    }
   
    private void drawClockPanel(Canvas canvas,float radius){   
        //System.out.println(getWidth()+":"+getHeight());
        //画钟的外圈
        canvas.drawCircle(cx, cy, radius, colorCirclePaint);
        //画钟的圆点
        canvas.drawCircle(cx, cy, radius/60, pointPaint);
        int hourLen = 12;
        int minLen = 60;
        for(int index = 0;index<hourLen;index++){
            drawMark(canvas,index,cx,cy,radius,radius-hourMarkLen,(2*Math.PI/hourLen)*index+Math.PI/2,hourMarkPaint,true);
        }
        for(int index = 0;index<minLen;index++){
            drawMark(canvas,index,cx,cy,radius,radius-minuteMarkLen,(2*Math.PI/minLen)*index+Math.PI/2,minuteMarkPaint,false);
        }
    }
   
    private void drawNeedle(Canvas canvas){
        double hourAngle = (2*Math.PI/12)*mHour+Math.PI/2+((2*Math.PI)/(12*60))*mMinute+((2*Math.PI)/(12*60*60))*mSecond;
        double minuteAngle = (2*Math.PI/(12*5))*mMinute+Math.PI/2+((2*Math.PI)/(12*5*60))*mSecond;
        double secondAngle = (2*Math.PI/60)*mSecond+Math.PI/2;
        drawNeedle(canvas,cx,cy,hourAngle,hourNeedleRadius,hourNeedlePaint);
        drawNeedle(canvas,cx,cy,minuteAngle,minuteNeedleRadius,minuteNeedlePaint);
        drawNeedle(canvas,cx,cy,secondAngle,secondNeedleRadius,secondNeedlePaint);
    }
   
    private void drawMark(Canvas canvas,int index,float cx,float cy,float r1,float r2,double angle,Paint paint,boolean drawNumber){
        float startX = (float)(cx-r2*Math.cos(angle));
        float startY = (float)(cy-r2*Math.sin(angle));
        float stopX = (float)(cx-r1*Math.cos(angle));
        float stopY = (float)(cy-r1*Math.sin(angle));
        float textSize = textPaint.getTextSize();
        float radiusText = r2 - textSize;
        if(index>=3 && index<=9){
            radiusText = r2-textSize/3;
        }
        float textX = (float)(cx-radiusText*Math.cos(angle));
        float textY = (float)(cy-radiusText*Math.sin(angle));
        if(index == 3 || index == 9){
            textY = textY + textSize/4;
        }
        canvas.drawLine(startX,startY,stopX,stopY, paint);
        if(drawNumber){
            if(index==0){
                index = 12;
            }
            canvas.drawText(String.valueOf(index), textX, textY, textPaint);
        }
    }
   
    private void drawNeedle(Canvas canvas,float cx,float cy,double angle,float radius,Paint paint){
        canvas.drawLine(cx, cy, (float)(cx-radius*Math.cos(angle)), (float)(cy-radius*Math.sin(angle)), paint);
    }

    public static Screen getScreenPix(Context context) {
        DisplayMetrics dm = new DisplayMetrics();
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        windowManager.getDefaultDisplay().getMetrics(dm);
        return new Screen(dm.widthPixels,dm.heightPixels);
    }
   
    public static class Screen{
       
        public int widthPixels;
        public int heightPixels;
       
        public Screen(){
           
        }
       
        public Screen(int widthPixels,int heightPixels){
            this.widthPixels=widthPixels;
            this.heightPixels=heightPixels;
        }

        @Override
        public String toString() {
            return "("+widthPixels+","+heightPixels+")";
        }
       
    }

    @Override
    public void run() {
        while(running){
            try {
                resetTime();
                postInvalidate();
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }   
        }
    }

}

布局文件main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:joydao="http://schemas.android.com/apk/res/net.joydao.clock"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <net.joydao.clock.view.ClockView
        android:id="@+id/joydaoClock" android:layout_width="wrap_content"
        android:layout_height="wrap_content" joydao:clockColor="#ffffff"
        joydao:visible="false" joydao:timeZone="beijing" />

</LinearLayout>

属性描述文件attrs.xml:

<?xml version="1.0" encoding="UTF-8"?>
<resources>
    <declare-styleable name="ClockView">
        <attr name="clockColor" format="color" />
        <attr name="visible" format="boolean"/>
        <attr name="timeZone" format="dimension">
            <enum name="londan" value="0" />
            <enum name="beijing" value="8" />
            <enum name="newyork" value="20" />
        </attr>
    </declare-styleable>
</resources>

效果图：