<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:id="@+id/activity_main"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:paddingBottom="@dimen/activity_vertical_margin"  android:paddingLeft="@dimen/activity_horizontal_margin"  android:paddingRight="@dimen/activity_horizontal_margin"  android:paddingTop="@dimen/activity_vertical_margin"  tools:context="com.bwie.test.xuejian1508a20170928.MainActivity">   <com.bwie.test.xuejian1508a20170928.ViView  android:layout_width="match_parent"  android:layout_height="match_parent"   /> </RelativeLayout>

public class ViView extends View{  Paint paint;  Context context;  //構造方法  public ViView(Context context) {  super(context);  }   public ViView(Context context, AttributeSet attrs) {  super(context, attrs);  }   public ViView(Context context, AttributeSet attrs, int defStyleAttr) {  super(context, attrs, defStyleAttr);  }   public ViView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {  super(context, attrs, defStyleAttr, defStyleRes);  this.context=context;  }   @Override  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  super.onMeasure(widthMeasureSpec, heightMeasureSpec);  }   @Override  protected void onLayout(boolean changed, int left, int top, int right, int bottom) {  super.onLayout(changed, left, top, right, bottom);   }   /*繪圖*/  @Override  protected void onDraw(Canvas canvas) {  super.onDraw(canvas);  //得到屏幕寬高  int width = getWidth();  int radius = width - 450/2;  int height = getHeight(); // 創建畫筆  Paint paint1 = new Paint();  Paint paint2 = new Paint();  Paint paint3= new Paint(); // 消除鋸齒  paint1.setAntiAlias(true);  paint2.setAntiAlias(true);  paint3.setAntiAlias(true);  //畫筆顏色  paint1.setColor(Color.RED);  paint2.setColor(Color.WHITE);  paint3.setColor(Color.BLUE); // 畫圓。確定位置 // canvas.drawRect(100,100,width/2,height/2,paint1); // canvas.drawCircle(100,100,100,paint1); // canvas.drawCircle(250,250,200,paint2); // canvas.drawCircle(500,500,300,paint3);  //設置圓環形狀和大小  RectF oval = new RectF(width-radius,width-radius,width+radius,width+radius);  paint1.setStrokeWidth(450);  canvas.drawArc(oval,-90,90,false,paint1);   canvas.drawCircle(width/2,height/2,450,paint1);  canvas.drawCircle(width/2,height/2,300,paint2);  canvas.drawCircle(width/2,height/2,200,paint3);  }   @Override  public boolean onTouchEvent(MotionEvent event) {  return super.onTouchEvent(event);  } }