好久沒寫部落格了，最近在寫一個專案時需要一個可以調節檔位的圓盤， 首先實現這個圓盤自定義View，首先在構造方法中定義畫筆，重寫onDraw(Canvas canvas)方法，進行繪製，首先繪製一個大圓，然後我這個大圓周圍的錶盤顯示一共有9個檔位，為了美觀，每個檔位裡面有8個小指標，這樣一個分為72份，也就是沒5°畫一次，由於我這個還需要有一個設定檔位的按鈕，所以新增檔位的檔位設定。
下面說一下滑動手勢的處理
我們可以在oNMeasure()方法得到該控制元件的大小，除以2就是圓心，我們設定的大圓的半徑為200，用圓心y座標減去200就是0檔位的y座標，通過獲取當前手勢位置，就可以通過這三個點構建三角形，通過初中學的餘弦定理可以求得滑動角度，當滑動到左半部分，角度注意要用360-當前角度。
螢幕適配看了hongyang大神Orz的適配方案，

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上程式碼

package com.example.yasin.dianretan.utils;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Handler;
import android.os.Message;
import
 
 android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

import com.example.yasin.dianretan.R;

import java.util.Calendar;

/**
 * Created by Yasin on 2016/4/7.
 */
public class CirclerView extends View {

    private int width;
    private int height;
    private
 
 Paint mPaintLine;
    private Paint mPaintCircle;
    private Paint mPaintSec;
    private Paint mPaintText,mPaintText2;
    private int dw;//當前檔位
    public static final int NEED_INVALIDATE = 0X23;
    private double cx,cy;//手勢座標
    private double yxx,yxy;//圓心
    private String name;
    private double jd;//滑動的角度

    //每隔一秒，在handler中呼叫一次重新繪製方法
    private Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {

            switch (msg.what){
                case NEED_INVALIDATE:
                    invalidate();//告訴UI主執行緒重新繪製
                    handler.sendEmptyMessageDelayed(NEED_INVALIDATE,1000);
                    break;
                default:
                    break;
            }
        }
    };

    public CirclerView(Context context) {
        super(context);
    }

    public CirclerView(Context context, AttributeSet attrs) {
        super(context, attrs);

        /*
        * 定義多個畫不同東西的畫筆
        * */
        mPaintLine = new Paint();
        mPaintLine.setColor(Color.WHITE);
        mPaintLine.setStrokeWidth(6);

        mPaintCircle = new Paint();
        mPaintCircle.setColor(context.getResources().getColor(R.color.yellow));//設定顏色
        mPaintCircle.setStrokeWidth(10);//設定線寬
        mPaintCircle.setAntiAlias(true);//設定是否抗鋸齒
        mPaintCircle.setStyle(Paint.Style.STROKE);//設定繪製風格


        mPaintText = new Paint();
        mPaintText.setColor(Color.WHITE);
        mPaintText.setStrokeWidth(10);
        mPaintText.setTextAlign(Paint.Align.CENTER);
        mPaintText.setTextSize(40);

        mPaintText2 = new Paint();
        mPaintText2.setColor(Color.WHITE);
        mPaintText2.setStrokeWidth(10);
        mPaintText2.setTextAlign(Paint.Align.CENTER);
        mPaintText2.setTextSize(60);

        //滑針
        mPaintSec = new Paint();
        mPaintSec.setStrokeWidth(10);
        mPaintSec.setColor(Color.YELLOW);


    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);
        height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        yxx = width/2;
        yxy = height/2;
        setMeasuredDimension(width, height);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        int circleRadius = 200;//大圓半徑
        //畫出大圓
        canvas.drawCircle(width / 2, height / 2, circleRadius, mPaintCircle);

        //依次旋轉畫布，畫出每個刻度和對應數字
        if(dw==0){
            mPaintText2.setColor(Color.RED);
            canvas.drawText("關",width/2,height/2+60,mPaintText2);
        }else{
            mPaintText2.setColor(Color.WHITE);
            canvas.drawText(dw+"檔",width/2,height/2+60,mPaintText2);
        }

        mPaintText2.setColor(Color.YELLOW);
        mPaintText2.setTextSize(40);
        canvas.drawText(name, width / 2, height / 2 - 50, mPaintText2);

        for (int i = 0; i <= 71; i++) {//一共有72個（刻度+檔位文字）
            canvas.save();//儲存當前畫布
            canvas.rotate(360 / 72 * i, width / 2, height / 2);
           // canvas.rotate((float)jd, width / 2, height / 2);
            if(i%8!=0) {
                if(i<dw*8||i<jd/5.0f){/*如果使用的檔位調節，則該檔位內的都有黃色；
                                         如果滑動的，一個刻度是5°,s所以個當前度數除以5*/
                    mPaintLine.setColor(Color.YELLOW);
                }else{
                    mPaintLine.setColor(Color.WHITE);
                }
                canvas.drawLine(width / 2, height / 2 - circleRadius-10, width / 2, height / 2 - circleRadius - 30, mPaintLine);
            }else {
                //左起：文字內容，起始位置x座標，起始位置y座標，畫筆
                if(i/8<=dw){
                    mPaintText.setColor(Color.YELLOW);
                }else{
                    mPaintText.setColor(Color.WHITE);
                }
                canvas.drawText("" + i / 8, width / 2, height / 2 - circleRadius - 20, mPaintText);
            }
            canvas.restore();
        }

        float secDegree = (float) jd;//dw/9f*360;//得到指標旋轉的角度
        canvas.save();
        canvas.rotate(secDegree, width / 2, height / 2);
        canvas.drawLine(width / 2, height / 2 - circleRadius, width / 2, height / 2 - circleRadius - 30, mPaintSec);

        canvas.restore();

    }

    public void setDw(int dw){
        this.dw = dw;
        //handler.sendEmptyMessage(NEED_INVALIDATE);//向handler傳送一個訊息，讓它開啟重繪
        this.jd = dw*40;
        invalidate();
    }
    public int getDw(){
        return dw;
    }

    public void setName(String name){
        this.name = name;
    }
    public String getName(){
        return name;
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        cx=event.getX();
        cy=event.getY();

        jd = getJD(cx,cy);
        if(cx<=yxx) {
            jd=180+(180-jd);
        }
        dw = (int) (jd/40);
        invalidate();
        return true;
    }

    /*
    * type 1表示得到距離，2表示得到的距離的平方
    * */
    private double getJL(double ax,double ay,double bx,double by,int type){
        if(type==1){
            return Math.sqrt(((ax-bx)*(ax-bx)+(ay-by)*(ay-by)));
        }else{
            return (((ax-bx)*(ax-bx)+(ay-by)*(ay-by)));
        }
    }
//計算角度
    private double getJD(double ax,double ay){
        return (Math.acos(((getJL(ax,ay,yxx,yxy,2)+200*200-getJL(ax,ay,yxx,(yxy-200),2))/(2*200*getJL(ax,ay,yxx,yxy,1))))*180/Math.PI);
    }

}

效果圖