使用 UIPopoverBackgroundView 类

类方法很简单:contentViewInsets返回你的边框的宽度(不包括箭头)，arrowHeight是你的高度箭头，arrowBase 是箭头的基础.

The class methods are straightforward: contentViewInsets returns the width of your borders all the way round (not including the arrow), arrowHeight is the height of your arrow, arrowBase is the base of your arrow.

• 背景视图的框架应该是 self.bounds，在箭头所在的边缘由 arrowHeight 插入
• 箭头视图的框架应对齐，使中心远离self中心arrowOffset(根据轴正确).如果箭头方向不向上，您必须更改图像方向，但我的弹出框只会向上，所以我没有这样做.

• The frame of your background view should be self.bounds, inset by arrowHeight on whatever edge the arrow is on
• The frame of the arrow view should be aligned so that the centre is arrowOffset away from the centre of self (correct according to the axis). You have to change the image orientation if the arrow direction is not up, but my popover would only be up so I didn't do that.

这是我的 Up-only 子类的 layoutSubviews 方法:

Here is the layoutSubviews method for my Up-only subclass:

-(void)layoutSubviews
{
    if (self.arrowDirection == UIPopoverArrowDirectionUp)
    {
        CGFloat height = [[self class] arrowHeight];
        CGFloat base = [[self class] arrowBase];

        self.background.frame = CGRectMake(0, height, self.frame.size.width, self.frame.size.height - height);

        self.arrow.frame = CGRectMake(self.frame.size.width * 0.5 + self.arrowOffset - base * 0.5, 1.0, base, height);
        [self bringSubviewToFront:self.arrow];

    }
}

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