在eoe看到有一篇關於雷達掃描的文章，然後看了下，很簡單，但是覺得還有很多可以優化的地方，下面貼出來

package com.example.wave;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Shader;
import android.graphics.SweepGradient;
import android.util.AttributeSet;
import android.widget.FrameLayout;

public class RadarView extends FrameLayout {

	private int viewSize = 500;
	private Paint mPaintLine;
	private Paint mPaintSector;
	private boolean isStart = false;
	private ScanThread mThread;
	private int start = 0;

	private final int paintWidth = 10;

	public RadarView(Context context) {
		super(context);
		init();
	}

	public RadarView(Context context, AttributeSet attrs) {
		super(context, attrs);
		init();
	}

	private void init() {
		initPaint();
		mThread = new ScanThread();
		setBackgroundColor(Color.TRANSPARENT);
	}

	private void initPaint() {
		mPaintLine = new Paint();
		mPaintLine.setStrokeWidth(paintWidth);
		mPaintLine.setAntiAlias(true);
		mPaintLine.setStyle(Style.STROKE);
		mPaintLine.setColor(0xffff0000);

		mPaintSector = new Paint();
		mPaintSector.setColor(0x9D00ff00);
		mPaintSector.setAntiAlias(true);
	}

	public void setViewSize(int size) {
		this.viewSize = size;
		mShader = new SweepGradient(viewSize >> 1, viewSize >> 1, Color.TRANSPARENT, Color.GREEN);
		setMeasuredDimension(viewSize, viewSize);
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		setMeasuredDimension(viewSize, viewSize);
	}

	public void start() {
		mThread.start();
		isStart = true;
	}

	public void stop() {
		if (isStart) {
			Thread.interrupted();
			isStart = false;
		}
	}

	private Shader mShader = new SweepGradient(viewSize >> 1, viewSize >> 1, Color.TRANSPARENT, Color.GREEN);
	private Matrix matrix = new Matrix();

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		int halfRadaSize = viewSize >> 1;
		canvas.drawCircle(halfRadaSize, halfRadaSize, halfRadaSize >> 1, mPaintLine);
		canvas.drawCircle(halfRadaSize, halfRadaSize, halfRadaSize - (paintWidth >> 1), mPaintLine);
		canvas.drawLine(halfRadaSize, 0, halfRadaSize, viewSize, mPaintLine);
		canvas.drawLine(0, halfRadaSize, viewSize, halfRadaSize, mPaintLine);
		mPaintSector.setShader(mShader);
		canvas.concat(matrix);
		canvas.drawCircle(halfRadaSize, halfRadaSize, halfRadaSize - paintWidth, mPaintSector);
	}

	protected class ScanThread extends Thread {

		int halfRadaSize = viewSize >> 1;
		
		@Override
		public void run() {
			while (isStart) {
				start = start + 2;
				matrix.reset();
				matrix.postRotate(start, halfRadaSize, halfRadaSize);
				postInvalidate();
				try {
					Thread.sleep(10);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		}
	}
}