在新浪微博上有一个雷达功能，感觉类似于微信附近的人。只是多了一个类似于雷达扫描效果的动画，某些知名安全软件也有这样的雷达效果，因此在这里学习一下。
首先看一下效果图，有个整体的印象
好了，为了便于理解，这里就按照动画所见内容依次展开来说
准备
这里决定采用canvas（画布）和paint（画笔）实现了这个简单动画控件。
由图片可以看到有两条交叉的十字线、几个圆圈和一些白点，那么首先定义一下所需的画笔，画布及一些数据
setBackgroundColor(Color.TRANSPARENT);
//宽度=5，抗锯齿，描边效果的白色画笔
mPaintLine = new Paint();
mPaintLine.setStrokeWidth(5);
mPaintLine.setAntiAlias(true);
mPaintLine.setStyle(Style.STROKE);
mPaintLine.setColor(Color.WHITE);
//宽度=5，抗锯齿，描边效果的浅绿色画笔
mPaintCircle = new Paint();
mPaintCircle.setStrokeWidth(5);
mPaintCircle.setAntiAlias(true);
mPaintCircle.setStyle(Style.FILL);
mPaintCircle.setColor(0x99000000);
//暗绿色的画笔
mPaintSector = new Paint();
mPaintSector.setColor(0x9D00ff00);
mPaintSector.setAntiAlias(true);
//定义一个暗绿色的梯度渲染
mShader = new SweepGradient(viewSize / 2, viewSize / 2, Color.TRANSPARENT, Color.GREEN);
mPaintSector.setShader(mShader);
//白色实心画笔
mPaintPoint=new Paint();
mPaintPoint.setColor(Color.WHITE);
mPaintPoint.setStyle(Style.FILL);
//随机生成一些数组点，模拟雷达扫描结果
point_x = UtilTools.Getrandomarray(15, 300);
point_y = UtilTools.Getrandomarray(15, 300);这里说一下这个SweepGradient
SweepGradient的构造函数：
public SweepGradient(float cx, float cy, int[] colors, float[] positions)public SweepGradient(float cx, float cy, int color0, int color1)其中cx,cy 指定圆心, color1,color0 或 colors 指定渐变的颜色 ，对于使用多于两种颜色时，还可以通过positions 指定每种颜色的相对位置，positions 设为NULL时表示颜色均匀分布。
绘制基本图形
canvas.drawCircle(viewSize / 2, viewSize / 2, 350, mPaintCircle);
canvas.drawCircle(viewSize / 2, viewSize / 2, 255, mPaintLine);
canvas.drawCircle(viewSize / 2, viewSize / 2, 125, mPaintLine);
canvas.drawCircle(viewSize / 2, viewSize / 2, 350, mPaintLine);
//绘制两条十字线
canvas.drawLine(viewSize / 2, 0, viewSize / 2, viewSize, mPaintLine);
canvas.drawLine(0, viewSize / 2, viewSize, viewSize / 2, mPaintLine);这样就绘制除了整个UI,接下来就上动画，就可以实现整体的效果。
动画实现
这里实现动画的时候，用到了Matrix这个东西，也就是矩阵。上学的时候，线性代数老师讲各种线性变换时，脑子里在想，这玩意是干嘛使得，现在总算是遇上了，现在看起来也是云里雾里。总的来说就是可以使用Matrix实现强大的图形动画，包括位移、旋转、缩放及透明变化等效果，有着一系列的setTranslate,setRotate,setScale等方法。很方便的实现图形各种变换。
对Matrix有兴趣的同学可以深入研究一下，
这篇博客
对此讲的很仔细（估计是学霸写的）。
protected class ScanThread extends Thread {
private RadarView view;
public ScanThread(RadarView view) {
// TODO Auto-generated constructor stub
this.view = view;
}
@Override
public void run() {
// TODO Auto-generated method stub
while (threadRunning) {
if (isstart) {
view.post(new Runnable() {
public void run() {
start = start + 1;
matrix = new Matrix();
//设定旋转角度,制定进行转转操作的圆心
// matrix.postRotate(start, viewSize / 2, viewSize / 2);
// matrix.setRotate(start,viewSize/2,viewSize/2);
matrix.preRotate(direction*start,viewSize/2,viewSize/2);
view.invalidate();
}
});
try {
Thread.sleep(5);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}首先，这里在一个独立线程中不断的对start做累加，作为旋转角度。然后将其和matrix关联。这里尝试使用了matrix的三个方法，暂时没有发现区别。
接下来在onDraw方法中不断绘制图形即可
//根据matrix中设定角度，不断绘制shader,呈现出一种扇形扫描效果
canvas.concat(matrix);
canvas.drawCircle(viewSize / 2, viewSize / 2, 350, mPaintSector);
最终实现
好了，最终整体的代码如下：
public class RadarView extends FrameLayout {
private Context mContext;
private int viewSize = 800;
private Paint mPaintLine;
private Paint mPaintCircle;
private Paint mPaintSector;
public boolean isstart = false;
private ScanThread mThread;
private Paint mPaintPoint;
//旋转效果起始角度
private int start = 0;
private int[] point_x;
private int[] point_y;
private Shader mShader;
private Matrix matrix;
public final static int CLOCK_WISE=1;
public final static int ANTI_CLOCK_WISE=-1;
@IntDef({ CLOCK_WISE, ANTI_CLOCK_WISE })
public @interface RADAR_DIRECTION {
}
//默认为顺时针呢
private final static int DEFAULT_DIERCTION=CLOCK_WISE;
//设定雷达扫描方向
private int direction=DEFAULT_DIERCTION;
private boolean threadRunning = true;
public RadarView(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
mContext = context;
initPaint();
}
public RadarView(Context context) {
super(context);
// TODO Auto-generated constructor stub
mContext = context;
initPaint();
}
private void initPaint() {
// TODO Auto-generated method stub
setBackgroundColor(Color.TRANSPARENT);
//宽度=5，抗锯齿，描边效果的白色画笔
mPaintLine = new Paint();
mPaintLine.setStrokeWidth(5);
mPaintLine.setAntiAlias(true);
mPaintLine.setStyle(Style.STROKE);
mPaintLine.setColor(Color.WHITE);
//宽度=5，抗锯齿，描边效果的浅绿色画笔
mPaintCircle = new Paint();
mPaintCircle.setStrokeWidth(5);
mPaintCircle.setAntiAlias(true);
mPaintCircle.setStyle(Style.FILL);
mPaintCircle.setColor(0x99000000);
//暗绿色的画笔
mPaintSector = new Paint();
mPaintSector.setColor(0x9D00ff00);
mPaintSector.setAntiAlias(true);
mShader = new SweepGradient(viewSize / 2, viewSize / 2, Color.TRANSPARENT, Color.GREEN);
mPaintSector.setShader(mShader);
//白色实心画笔
mPaintPoint=new Paint();
mPaintPoint.setColor(Color.WHITE);
mPaintPoint.setStyle(Style.FILL);
//随机生成的点，模拟雷达扫描结果
point_x = UtilTools.Getrandomarray(15, 300);
point_y = UtilTools.Getrandomarray(15, 300);
}
public void setViewSize(int size) {
this.viewSize = size;
setMeasuredDimension(viewSize, viewSize);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// TODO Auto-generated method stub
setMeasuredDimension(viewSize, viewSize);
}
public void start() {
mThread = new ScanThread(this);
mThread.setName("radar");
mThread.start();
threadRunning = true;
isstart = true;
}
public void stop() {
if (isstart) {
threadRunning = false;
isstart = false;
}
}
@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
canvas.drawCircle(viewSize / 2, viewSize / 2, 350, mPaintCircle);
canvas.drawCircle(viewSize / 2, viewSize / 2, 255, mPaintLine);
canvas.drawCircle(viewSize / 2, viewSize / 2, 125, mPaintLine);
canvas.drawCircle(viewSize / 2, viewSize / 2, 350, mPaintLine);
//绘制两条十字线
canvas.drawLine(viewSize / 2, 0, viewSize / 2, viewSize, mPaintLine);
canvas.drawLine(0, viewSize / 2, viewSize, viewSize / 2, mPaintLine);
//这里在雷达扫描过制定圆周度数后，将随机绘制一些白点，模拟搜索结果
if (start > 100) {
for (int i = 0; i < 2; i++) {
canvas.drawCircle(viewSize / 2 + point_x[i], viewSize / 2 + point_y[i], 10, mPaintPoint);
}
}
if (start > 200) {
for (int i = 2; i < 5; i++) {
canvas.drawCircle(viewSize / 2 + point_x[i], viewSize / 2 + point_y[i], 10, mPaintPoint);
}
}
if (start > 300) {
for (int i = 5; i < 9; i++) {
canvas.drawCircle(viewSize / 2 + point_x[i], viewSize / 2 + point_y[i], 10, mPaintPoint);
}
}
if (start > 500) {
for (int i = 9; i < 11; i++) {
canvas.drawCircle(viewSize / 2 + point_x[i], viewSize / 2 + point_y[i], 10, mPaintPoint);
}
}
if (start > 800) {
for (int i = 11; i < point_x.length; i++) {
canvas.drawCircle(viewSize / 2 + point_x[i], viewSize / 2 + point_y[i], 10, mPaintPoint);
}
}
//根据matrix中设定角度，不断绘制shader,呈现出一种扇形扫描效果
canvas.concat(matrix);
canvas.drawCircle(viewSize / 2, viewSize / 2, 350, mPaintSector);
super.onDraw(canvas);
}
public void setDirection(@RADAR_DIRECTION int direction) {
if (direction != CLOCK_WISE && direction != ANTI_CLOCK_WISE) {
throw new IllegalArgumentException("Use @RADAR_DIRECTION constants only!");
}
this.direction = direction;
}
protected class ScanThread extends Thread {
private RadarView view;
public ScanThread(RadarView view) {
// TODO Auto-generated constructor stub
this.view = view;
}
@Override
public void run() {
// TODO Auto-generated method stub
while (threadRunning) {
if (isstart) {
view.post(new Runnable() {
public void run() {
start = start + 1;
matrix = new Matrix();
//设定旋转角度,制定进行转转操作的圆心
// matrix.postRotate(start, viewSize / 2, viewSize / 2);
// matrix.setRotate(start,viewSize/2,viewSize/2);
matrix.preRotate(direction*start,viewSize/2,viewSize/2);
view.invalidate();
}
});
try {
Thread.sleep(5);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
}
说明
多余的部分就不再解释，代码里已经注释的很清楚。这个RadarView的使用也是很简单
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RadarView radarView = (RadarView) findViewById(R.id.radar);
//设置雷达扫描方向
radarView.setDirection(RadarView.ANTI_CLOCK_WISE);
radarView.start();
}这里雷达ViewSize设置为800，所以在布局文件中设定大小时将不起作用，正常使用时，需根据实际需求调整viewsize大小和几个Circle的半径，从而达到更有好的UI.
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