雷达.gif
定义一些变量
代码语言：javascript复制 private int width, height, radius;
private SweepGradient sweepGradient;
private Paint paint = new Paint();
private Matrix matrix = new Matrix();
//递增的角度
private int FACTOR = 2;
private int RATIO = 0;
//背景paint
private Paint bgPaint = new Paint();在onlayout中初始化参数
代码语言：javascript复制 @Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
width = getMeasuredWidth();
height = getMeasuredHeight();
radius = (int) (Math.min(width, height) / 2.0f);
sweepGradient = new SweepGradient(radius, radius, new int[]{Color.GREEN, Color.TRANSPARENT}, null);
paint.setShader(sweepGradient);
paint.setAntiAlias(true);
bgPaint.setStyle(Paint.Style.STROKE);
bgPaint.setAntiAlias(true);
bgPaint.setColor(Color.WHITE);
bgPaint.setStrokeWidth(2);
bgPaint.setPathEffect(new DashPathEffect(new float[]{10, 10}, 0));
}ondraw中利用使用sweepGradient 的paint画圆，并利用matrix旋转变换实现旋转
代码语言：javascript复制 @Override
protected void onDraw(Canvas canvas) {
canvas.drawCircle(radius, radius, radius, paint);
drawBackGround(canvas);
RATIO = FACTOR;
if (RATIO == 360) {
RATIO = 0;
}
matrix.setRotate(RATIO, radius, radius);
sweepGradient.setLocalMatrix(matrix);
postInvalidateDelayed(10);
}
/**
* 画背景
*
* @param canvas
*/
private void drawBackGround(Canvas canvas) {
canvas.drawCircle(radius, radius, radius, bgPaint);
canvas.drawCircle(radius, radius, radius / 4.0f, bgPaint);
canvas.drawCircle(radius, radius, radius * 2.0f / 4.0f, bgPaint);
canvas.drawCircle(radius, radius, radius * 3.0f / 4.0f, bgPaint);
canvas.drawPoint(radius, radius, bgPaint);
Path path_h = new Path();
path_h.moveTo(0, radius);
path_h.lineTo(radius * 2, radius);
canvas.drawPath(path_h, bgPaint);
Path path_v = new Path();
path_v.moveTo(radius, 0);
path_v.lineTo(radius, radius * 2);
canvas.drawPath(path_v, bgPaint);
}
