<?xml version="1.0" encoding="UTF-8"?> 
 
  
  

  
  

class RoundCornerDrawable extends Drawable {

 final int color;
 final float radius;
 final Paint paint;
 final RectF rectF;

 RoundCornerDrawable(int color, float radius) {
  this.color = color;
  this.radius = radius;

  // 实心的画笔
  this.paint = new Paint();
  paint.setStyle(Paint.Style.FILL);
  paint.setAntiAlias(true);
  paint.setColor(color);

  this.rectF = new RectF();
 }

 // 用于设置Drawable宽高
 public void setRect(int width, int height) {
  this.rectF.left = 0;
  this.rectF.top = 0;
  this.rectF.right = width;
  this.rectF.bottom = height;
 }

 @Override
 public void draw(@NonNull Canvas canvas) {
  canvas.drawRoundRect(rectF, radius, radius, paint); // 画圆角矩形，现成的方法
 }

 // 其余方法略
}

public class RoundCornerButton extends AppCompatButton {

 private int colorNormal;
 private float cornerRadius;
 private RoundCornerDrawable bgDrawableNormal = null;

 // 省略三个构造方法
 // 构造方法最后一定要调用initCornerBackground完成初始化

 private void initCornerBackground(AttributeSet attrs, int defStyleAttr) {
  TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.RoundCornerButton, defStyleAttr, 0);

  this.cornerRadius = a.getDimension(R.styleable.RoundCornerButton_rcb_cornerRadius, 0);
  this.colorNormal = a.getColor(R.styleable.RoundCornerButton_rcb_backgroundColor, 0);
  makeBackgroundDrawable();

  a.recycle();
 }

 private void makeBackgroundDrawable() {
  bgDrawableNormal = new RoundCornerDrawable(this.colorNormal, this.cornerRadius);
  bgDrawableNormal.setRect(getWidth(), getHeight());

  // 设计通常会给出禁用时的样式以及按下时的样式
  // 所以这里用使用StateListDrawable
  StateListDrawable bgDrawable = new StateListDrawable();
  bgDrawable.addState(new int[]{android.R.attr.state_enabled, -android.R.attr.state_pressed}, bgDrawableNormal);
  // 每多一种状态，在这里多加一项
  setBackgroundDrawable(bgDrawable);
 }

 @Override
 protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
  super.onLayout(changed, left, top, right, bottom);

  // layout之后必然会draw，所以在这里设置drawable的尺寸
  if (bgDrawableNormal != null) {
   bgDrawableNormal.setRect(right - left, bottom - top);
  }
  // 每多一种状态，在这里多加一项
 }
}