现在系统已经提供了评分控件，所以我建议还是用系统比较好。我在这里自定义，只是加深对自定义控件的理解，有助于自我提升。

1.还是老套路，自定义属性

需要两张图片资源

 <declare-styleable name="RatingBar">
    <attr name="starNormal" format="reference"/>
    <attr name="starFocus" format="reference"/>
    <attr name="gradeNumber" format="integer"/>
 </declare-styleable >

创建RatingBar

 public class RatingBar extends View {
private Bitmap mStarNormalBitmap, mStarFocusBitmap;
private int mGradeNumber = 5;
public RatingBar(Context context) {
    this(context, null);
}

public RatingBar(Context context, AttributeSet attrs) {
    this(context, attrs,0);
}

public RatingBar(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.RatingBar);
    int starNormalId = array.getResourceId(R.styleable.RatingBar_starNormal, 0);
    if (starNormalId == 0) {
        throw new RuntimeException("请设置属性 starNormal ");
    }
    mStarNormalBitmap = BitmapFactory.decodeResource(getResources(), starNormalId);

    int starFocusId = array.getResourceId(R.styleable.RatingBar_starFocus, 0);
    if (starFocusId == 0) {
        throw new RuntimeException("请设置属性 starFocus ");
    }
    mStarFocusBitmap = BitmapFactory.decodeResource(getResources(), starFocusId);

    mGradeNumber = array.getInt(R.styleable.RatingBar_gradeNumber, mGradeNumber);
}

2.测量方法

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

    int height = mStarFocusBitmap.getHeight();
    int width = mStarFocusBitmap.getWidth() * mGradeNumber+getPaddingLeft()+getPaddingRight();
    setMeasuredDimension(width, height);
 }

3.绘制

 @Override
 protected void onDraw(Canvas canvas) {

    for (int i = 0; i < mGradeNumber; i++) {
        // i*星星的宽度
        int x= i * mStarFocusBitmap.getWidth();;

        // 结合第二个步骤 触摸的时候mCurrentGrade值是不断变化
        if(mCurrentGrade>i){// 1  01
            // 当前分数之前
            canvas.drawBitmap(mStarFocusBitmap, x, 0, null);
        }else{
            canvas.drawBitmap(mStarNormalBitmap, x, 0, null);
        }
    }
}

4.触摸事件

  @Override
  public boolean onTouchEvent(MotionEvent event) {

    // 移动 按下 抬起 处理逻辑都是一样，判断手指的位置，根据当前位置计算出分数，再去刷新显示
    switch (event.getAction()) {
        case MotionEvent.ACTION_MOVE: // 移动
            float moveX = event.getX();//event.getX()相对于当前控件的位置   event.getRawX()获取幕的x位置
            // 计算分数
            int currentGrade = (int) (moveX/mStarFocusBitmap.getWidth()+1);
            // 范围问题
            if(currentGrade<0){
                currentGrade = 0;
            }
            if(currentGrade>mGradeNumber){
                currentGrade = mGradeNumber;
            }
            // 分数相同的情况下不要绘制了 , 尽量减少onDraw()的调用
            if(currentGrade == mCurrentGrade){
                return true;
            }
            // 再去刷新显示
            mCurrentGrade = currentGrade;
            invalidate();
            break;
    }
    return true;
}