import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.DashPathEffect;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class CustView extends View{

  private Paint mPaint; //定义画笔

  public CustView(Context context, AttributeSet attrs) {
    super(context, attrs);

    //初始化画笔
    initPaint();
    setLayerType(View.LAYER_TYPE_SOFTWARE, mPaint); //4.0以上关闭硬件加速，否则虚线不显示
  }

  private void initPaint() {
    mPaint = new Paint();
    mPaint.setAntiAlias(true); //设置抗锯齿的效果
    mPaint.setStyle(Paint.Style.STROKE); //设置画笔样式为描边
    mPaint.setStrokeWidth(3); //设置笔刷的粗细度
    mPaint.setColor(Color.RED); //设置画笔的颜色
    mPaint.setPathEffect(new DashPathEffect(new float[]{5,5,5,5}, 1)); //设置画笔的路径效果为虚线效果
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    canvas.drawLine(0, 0, 100, 0, mPaint);
  }
}

<com.test.CustView
  android:layout_width="100dp"
  android:layout_height="10dp"
  android:layout_marginTop="10dp" />

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    canvas.drawCircle(50, 50, 50, mPaint); //画一个外圆
    mPaint.setColor(Color.WHITE);      //重新设置画笔颜色
    canvas.drawCircle(50, 50, 30, mPaint); //画一个内圆
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    RectF rect = new RectF(0, 0, 80, 60);
    canvas.drawRect(rect, mPaint);
  }