雷达扫描效果SweepGradient的使用

public class RadarScanView extends View {
private static final int defaultWidth=200;//默认宽度
private static final int defaultHeight=200;//默认高度
private Paint fillPaint;
private Paint stokePaint;
private Paint shadePaint;

private SweepGradient sweepGradient;//扫描渐变
private int centerX;//圆心的x坐标
private int centerY;//圆心的y坐标
private int radius;//圆的半径
private int num = 3;//圆环数
//雷达扫描时候的起始和终止颜色
private int mStartColor = 0x00000000;
private int mEndColor = 0xff000000;
private Matrix matrix;

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

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

private void init() {
//初始化填充画笔
fillPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
fillPaint.setStyle(Paint.Style.FILL);
fillPaint.setColor(Color.LTGRAY);
//初始化描边画笔
stokePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
stokePaint.setStyle(Paint.Style.STROKE);
stokePaint.setColor(Color.BLACK);
//初始化扫描区域画笔
shadePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
shadePaint.setStyle(Paint.Style.FILL);
shadePaint.setColor(Color.BLACK);
shadePaint.setStrokeWidth(2);
//初始化矩阵
matrix = new Matrix();
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int widthSpec=MeasureSpec.getMode(widthMeasureSpec);
int widthSize=MeasureSpec.getSize(widthMeasureSpec);
int heightSpec=MeasureSpec.getMode(heightMeasureSpec);
int heightSize=MeasureSpec.getSize(heightMeasureSpec);

int measureWidth=0;
int measureHeight=0;

if(widthSpec==MeasureSpec.EXACTLY){
measureWidth=widthSize;
}else {
measureWidth=defaultWidth;
}
if(heightSpec==MeasureSpec.EXACTLY){
measureHeight=heightSize;
}else{
measureHeight=defaultHeight;
}
setMeasuredDimension(measureWidth,measureHeight);
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
centerX = getWidth() / 2;
centerY = getWidth() / 2;
radius = getWidth() / 2;

shadePaint.setShader(null);
//将画布原点平移到控件的中心位置
canvas.translate(centerX, centerY);
//绘制底部背景圆
canvas.drawCircle(0, 0, radius, fillPaint);
//根据圆环数绘制圆环
for (int i = 0; i < num; i++) {
int h_radius = radius - i * radius / num;
canvas.drawCircle(0, 0, h_radius, stokePaint);
}
canvas.drawLine(-radius, 0, radius, 0, stokePaint);
canvas.drawLine(0, -radius, 0, radius, stokePaint);
//设置扫面渐变
sweepGradient = new SweepGradient(0, 0, mStartColor, mEndColor);
shadePaint.setShader(sweepGradient);
//绘制扫描渐变圆
canvas.concat(matrix);
canvas.drawCircle(0, 0, radius, shadePaint);
//调用循环扫描
scan();

}
//旋转角度

4000
private int rotate;

private void scan() {
//不断改变角度，并重绘控件
rotate += 3;
postInvalidateDelayed(20);
//重置矩阵
matrix.reset();
//设置旋转角度
matrix.setRotate(rotate);
}
}