看到CSDN這一論壇的問題，好奇地去把它解決了。看了一下時間都是一年前了。

MyActivity.java

package com.example.abcd;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.DashPathEffect;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Path;
import android.graphics.PathEffect;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.SweepGradient;
import android.os.Bundle;
import android.view.View;

public class MyActivity extends Activity{
	    @Override
	    protected void onCreate(Bundle savedInstanceState) {
	        super.onCreate(savedInstanceState);
	        setContentView(new SampleView(this));
	    }

	    @SuppressLint("DrawAllocation")
		private static class SampleView extends View {
	        private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
	        private float mRotate;
	        private Matrix mMatrix = new Matrix();
	        private Shader mShader;

	        public SampleView(Context context) {
	            super(context);
	            setFocusable(true);
	            setFocusableInTouchMode(true);
	            float x = 160;
	            float y = 100;
	            mShader = new SweepGradient(x, y, new int[] {0xFF09F68C,
	                                                  0xFFB0F44B,
	                                                  0xFFE8DD30,
	                                                  0xFFF1CA2E,
	                                                  0xFFFF902F,
	                                                  0xFFFF6433}, null);
	            mPaint.setShader(mShader);
	            mPaint.setStyle(Style.STROKE);
	            PathEffect effect = new DashPathEffect(new float[] { 2, 3, 2,3}, 1);
	            mPaint.setPathEffect(effect);
	            mPaint.setStrokeWidth(40);
	        }
	        public void getArc(Canvas canvas,float o_x,float o_y,float r,
	        		float startangel,float endangel,Paint paint){
	        	RectF rect = new RectF(o_x - r, o_y - r, o_x + r, o_y + r);
	        	Path path = new Path();
                path.moveTo(o_x,o_y);
                path.lineTo((float)(o_x+r*Math.cos(startangel*Math.PI/180))
                		  , (float)(o_y+r*Math.sin(startangel*Math.PI/180)));
                path.lineTo((float)(o_x+r*Math.cos(endangel*Math.PI/180))
                		  , (float)(o_y+r*Math.sin(endangel*Math.PI/180)));
                path.addArc(rect, startangel, endangel-startangel);
                canvas.clipPath(path);
                canvas.drawCircle(o_x, o_y, r, paint);
	        }
	        @Override 
	        protected void onDraw(Canvas canvas) {
	            Paint paint = mPaint;
	            float x = 160;
	            float y = 100;

	            canvas.drawColor(Color.WHITE);

	            mMatrix.setRotate(mRotate, x, y);
	            mShader.setLocalMatrix(mMatrix);
	            mRotate += 3;
	            if (mRotate >= 360) {
	                mRotate = 0;
	            }
	            invalidate();
	            getArc(canvas,x,y,80,135,405,paint);
	        }
	    }
}