前言：类似社交软件的雷达搜索：

MainActivity：

public class MainActivity extends Activity {
    private RadarView radarView;
    private Button btn;
    private Thread radarSweepThread;
    private boolean startRadar = true;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        radarView = (RadarView) findViewById(R.id.radar);
        btn = (Button) findViewById(R.id.btn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                if (startRadar) {
                    btn.setText("end");
                    radarView.setVisibility(View.VISIBLE);// 设置可见
                    Animation radarAnimEnter = AnimationUtils.loadAnimation(
                            MainActivity.this, R.anim.radar_anim_enter);// 初始化radarView进入动画
                    radarView.startAnimation(radarAnimEnter);// 开始进入动画
                    radarSweepThread = new Thread(new RadarSweep());// 雷达扫描线程
                    radarSweepThread.start();
                    startRadar = false;
                } else {
                    btn.setText("start");
                    Animation radarAnimEnter = AnimationUtils.loadAnimation(
                            MainActivity.this, R.anim.radar_anim_exit);// 初始化radarView退出动画
                    radarView.startAnimation(radarAnimEnter);// 开始进入动画
                    radarView.setVisibility(View.INVISIBLE);// 设置不可见
                    radarSweepThread.interrupt();// 停止扫描更新
                    startRadar = true;
                }
            }
        });
    }
    /**
     * @ClassName RadarSweep
     * @Description 雷达扫描动画刷新线程类
     */
    private class RadarSweep implements Runnable {
        int i = 1;
        @Override
        public void run() {
            // TODO Auto-generated method stub
            //无限判断当前线程状态，如果没有中断，就一直执行while内容
            //如果中断返回true，否则返回false
            while (!Thread.currentThread().isInterrupted() && i == 1) {
                try {
                    radarView.postInvalidate();// 刷新radarView, 执行onDraw();
                    Thread.sleep(10);// 暂停当前线程，更新UI线程（注释掉貌似没影响）
                } catch (InterruptedException e) {
                    i = 0;// 结束当前扫描线程标志符
                    break;
                }
            }
        }
    }
}

自定义View：

public class RadarView extends View {
    private Paint circlePaint;// 圆形画笔
    private Paint linePaint;// 线形画笔
    private Paint sweepPaint;// 扫描画笔
    SweepGradient sweepGradient;// 扇形渐变Shader
    int degree = 0;
    public RadarView(Context context) {
        super(context);
    }
    public RadarView(Context context, AttributeSet att) {
        super(context, att);
        initPaint();
    }
    /**
     * @param
     * @return void
     * @Description //初始化定义的画笔
     */
    private void initPaint() {
        Resources r = this.getResources();
        circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);// 圆形画笔，设置Paint为抗锯齿
        circlePaint.setARGB(255, 50, 57, 74);// 设置透明度和RGB颜色
        circlePaint.setStrokeWidth(3);// 轮廓宽度
        circlePaint.setStyle(Paint.Style.STROKE);
        linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);// 线性画笔
        linePaint.setStrokeCap(Paint.Cap.ROUND);
        linePaint.setARGB(150, 50, 57, 74);
        linePaint.setStrokeWidth(2);
        sweepPaint = new Paint(Paint.ANTI_ALIAS_FLAG);// 雷达Shader画笔
        sweepPaint.setStrokeCap(Paint.Cap.ROUND);
        sweepPaint.setStrokeWidth(4);
        sweepGradient = new SweepGradient(0, 0,
                r.getColor(R.color.start_color), r.getColor(R.color.end_color));
        sweepPaint.setShader(sweepGradient);//绘制梯度渐变，这里是渐变设置的方法
    }
    @Override
    protected void onMeasure(int wMeasureSpec, int hMeasureSpec) {
        int width = MeasureSpec.getSize(wMeasureSpec);
        int height = MeasureSpec.getSize(hMeasureSpec);
        int d = (width >= height) ? height : width; // 获取最短的边作为直径
        setMeasuredDimension(d, d); // 重写测量方法，保证获得的画布是正方形
    }
    @Override
    protected void onDraw(Canvas canvas) {
        int Width = getMeasuredWidth();// //计算控件的中心位置
        int Height = getMeasuredHeight();
        int pointX = Width / 2;// 获得圆心坐标
        int pointY = Height / 2;
        int radius = (pointX >= pointY) ? pointY : pointX;// 设置半径
        radius -= 10;// 设置半径
        canvas.save();// 保存Canvas坐标原点
        degree += 5;// 扫描旋转增量度数
        canvas.translate(pointX, pointY);// 设置旋转的原点
        canvas.rotate(270 + degree);
        canvas.drawCircle(0, 0, radius, sweepPaint);// 绘制扫描区域
        canvas.restore();// 恢复原Canvas坐标(0,0)
        canvas.drawCircle(pointX, pointY, radius, circlePaint);// 绘制3个嵌套同心圆形，使用circlePaint画笔
        circlePaint.setAlpha(100);// 降低内部圆形的透明度
        circlePaint.setStrokeWidth(2);// 轮廓宽度
        canvas.drawCircle(pointX, pointY, radius * 2 / 3, circlePaint);
        canvas.drawCircle(pointX, pointY, radius / 3, circlePaint);
        canvas.drawLine(pointX, 10, pointX, 2 * radius + 10, linePaint);// 绘制十字分割线
                                                                        // ， 竖线
        canvas.drawLine(10, pointY, 2 * radius + 10, pointY, linePaint);
        canvas.save();// 保存Canvas坐标原点
        canvas.translate(10, radius + 10);// 设置相对横线起始坐标
        float s = radius / 12f;// 刻度间距
        float minlength = s / 2;// 短刻度线长度
        float maxlength = s;// 长刻度线长度
        for (int i = 0; i < 24; i++) {
            float fromX, toX;
            fromX = toX = s * i;
            if (i % 4 != 0) {// 与圆形重叠处不画刻度
                if (i % 2 != 0) {
                    canvas.drawLine(fromX, -minlength, toX, minlength,
                            linePaint);// 绘制X轴短刻度
                } else {
                    canvas.drawLine(fromX, -maxlength, toX, maxlength,
                            linePaint);// 绘制X轴长刻度
                }
            }
        }
        canvas.restore();
        canvas.translate(pointX, 10);// 设置相对竖线起始坐标
        for (int i = 0; i < 24; i++) {
            float fromY, toY;
            fromY = toY = s * i;
            if (i % 4 != 0) {
                if (i % 2 != 0) {
                    canvas.drawLine(-minlength, fromY, minlength, toY,
                            linePaint);// 绘制Y短轴刻度
                } else {
                    canvas.drawLine(-maxlength, fromY, maxlength, toY,
                            linePaint);// 绘制Y长轴刻度
                }
            }
        }
    }
}

进入动画：radar_anim_enter.xml

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- 雷达动画由大到正常 -->  
    <scale  
        android:duration="2000"  
        android:fromXScale="1.5"  
        android:fromYScale="1.5"  
        android:interpolator="@android:anim/decelerate_interpolator"  
        android:pivotX="50%"  
        android:pivotY="50%"  
        android:toXScale="1.0"  
        android:toYScale="1.0" />
</set>

退出动画：radar_anim_exit.xml

<?xml version="1.0" encoding="utf-8"?>  
<set xmlns:android="http://schemas.android.com/apk/res/android" >  
    <!-- 雷达动画由正常到缩小退出 -->  
    <scale  
        android:duration="1000"  
        android:fromXScale="1.0"  
        android:fromYScale="1.0"  
        android:interpolator="@android:anim/accelerate_interpolator"  
        android:pivotX="50%"  
        android:pivotY="50%"  
        android:toXScale="0.0"  
        android:toYScale="0.0" />  
</set>