仿微信雷达寻好友动画

先看看要实现的效果：



这种效果正是类似微信上雷达寻找好友的动画，于是解压微信看看里面，发现微信是用一张图片做的旋转动画，于是乎看看这种特效，可以用画笔直接画出来，首先是四个圆，然后中间那部分扫描区便是颜色由透明渐变到淡白。比较简单。

public class RaderView extends View {
    private Paint mPaintCircleLine;//绘制圆边
    private Paint mPaintCircle;
    private int width;
    private int height;
    private Matrix matrix;
    private int start;
    private Handler handler = new Handler();
    private Runnable run = new Runnable() {
        @Override
        public void run() {
            start += 1;
            matrix = new Matrix();
            matrix.postRotate(start, width / 2, height / 2);
            RaderView.this.invalidate();//刷新重绘
            handler.postDelayed(run,30);
        }
    };

    public RaderView(Context context) {
        this(context, null);
    }

    public RaderView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public RaderView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initPaint();
        //得到当前屏幕的像素宽高
        width = context.getResources().getDisplayMetrics().widthPixels;
        height = context.getResources().getDisplayMetrics().heightPixels;
        matrix = new Matrix();
        handler.post(run);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(width, height);//设置该控件的宽高为当前屏幕的宽高
    }

    private void initPaint() {
        mPaintCircleLine = new Paint();
        mPaintCircleLine.setColor(Color.parseColor("#a2a2a2"));
        mPaintCircleLine.setAntiAlias(true);//抗锯齿
        mPaintCircleLine.setStyle(Paint.Style.STROKE);//设置实心
        mPaintCircleLine.setStrokeWidth(2);//画笔宽度

        mPaintCircle = new Paint();
        mPaintCircle.setColor(Color.parseColor("#99a2a2a2"));
        mPaintCircle.setAntiAlias(true);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //分别绘制四个圆
        canvas.drawCircle(width / 2, height / 2, height / 7, mPaintCircleLine);
        canvas.drawCircle(width / 2, height / 2, height / 4, mPaintCircleLine);
        canvas.drawCircle(width / 2, height / 2, height / 3, mPaintCircleLine);
        canvas.drawCircle(width / 2, height / 2, 3 * height / 7, mPaintCircleLine);
        //设置颜色渐变从透明到不透明
        Shader shader = new SweepGradient(width / 2, height / 2, Color.TRANSPARENT, Color.parseColor("#50aaaaaa"));
        mPaintCircle.setShader(shader);
        canvas.concat(matrix);
        canvas.drawCircle(width / 2, height / 2, 3 * height / 7, mPaintCircle);
    }
}

布局文件：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@mipmap/bg"
    tools:context=".MainActivity">
    <com.example.raderanim.RaderView
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</FrameLayout>

这就是整个的动画效果，可以直接拿来用，加张背景就完全ok了。