public class CustomeRectView extends View {
 private Paint mPiant;//定義畫筆對象
 private int rectColor;//矩形的顏色
 private int rectHeight;//矩形的高度
 private int rectWidth;//矩形的寬度
 public CustomeRectView(Context context) {
  this(context, null);
 }
 public CustomeRectView(Context context, @Nullable AttributeSet attrs) {
  this(context, attrs, 0);
 }
 public CustomeRectView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  /**
   * 獲取我們自定義的屬性
   */
  TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.CustomeRectView, defStyleAttr, 0);
  int arrayCount = array.getIndexCount();
  for (int i = 0; i < arrayCount; i++) {
   int index = array.getIndex(i);
   switch (index) {
    case R.styleable.CustomeRectView_rectColor:
     //getColor(int index，int defaultValue)
     rectColor=array.getColor(R.styleable.CustomeRectView_rectColor, Color.BLACK);
     break;
    case R.styleable.CustomeRectView_rectHeight:
     /**
      * 獲取dimension值得時候會有3個不同的方法getDimension()、getDimensionPixelSize()和getDimenPixelOffset()
      * 結果值都是將資源文件中定義的dip值乘以屏幕密度,即rectHeight*屏幕密度，只是getDimension()返回的是float，
      * 其余兩個返回的是int, 其中getDimensionPixelSize()返回的是實際數值的四舍五入,
      * 而getDimensionPixelOffset返回的是實際數值去掉后面的小數點;
      */
     rectHeight=array.getDimensionPixelOffset(R.styleable.CustomeRectView_rectHeight,200);
     break;
    case R.styleable.CustomeRectView_rectWidth:
     rectWidth=array.getDimensionPixelOffset(R.styleable.CustomeRectView_rectWidth,200);
     break;
   }
  }
  array.recycle();
 }
}

@Override
protected void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 mPiant=new Paint();
 mPiant.setColor(rectColor);//設置畫筆的顏色
 mPiant.setStyle(Paint.Style.FILL);//設置畫筆的樣式
 mPiant.setAntiAlias(true);//去除鋸齒
 /**
  * Draw the specified Rect using the specified paint. The rectangle will
  * be filled or framed based on the Style in the paint.
  *
  * @param left The left side of the rectangle to be drawn
  * @param top The top side of the rectangle to be drawn
  * @param right The right side of the rectangle to be drawn
  * @param bottom The bottom side of the rectangle to be drawn
  * @param paint The paint used to draw the rect
  */
 canvas.drawRect(0,0,getWidth(),getHeight(),mPiant);
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}

@Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  int widthMode=MeasureSpec.getMode(widthMeasureSpec);
  int widthSize=MeasureSpec.getSize(widthMeasureSpec);
  int heightMode=MeasureSpec.getMode(heightMeasureSpec);
  int heightSize=MeasureSpec.getSize(heightMeasureSpec);
  int width;
  int height;

  //如果設置了明確的大小
  if(widthMode==MeasureSpec.EXACTLY){
   width=widthSize;
  }else{
   //設置寬
   width=dpToPx(getContext(),200);
  }

  if(heightMode==MeasureSpec.EXACTLY){
  height=heightSize;
  }else{
  //設置高
   height=dpToPx(getContext(),200);
  }

  setMeasuredDimension(width,height);
 }
 
 /**
 * 根據手機的分辨率從 dp 的單位 轉成為 px(像素)
 */
 public int dpToPx(Context context, float dpValue){
  final float scale=context.getResources().getDisplayMetrics().density;
  return (int)(dpValue*scale+0.5f);
 }