1  首先繼承UIButton

2 實現imageRectForContentRect  titleRectForContentRect

// 內部圖片的frame
- (CGRect)imageRectForContentRect:(CGRect)contentRect
{
    CGFloat imageW = contentRect.size.width;
    CGFloat imageH = contentRect.size.height * IWTabBarButtonImageRatio;
    return CGRectMake(0, 0, imageW, imageH);
}


// 內部文字的frame
- (CGRect)titleRectForContentRect:(CGRect)contentRect
{
    CGFloat titleY = contentRect.size.height * IWTabBarButtonImageRatio;
    CGFloat titleW = contentRect.size.width;
    CGFloat titleH = contentRect.size.height - titleY;
    return CGRectMake(0, titleY, titleW, titleH);
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // 圖示居中
        self.imageView.contentMode = UIViewContentModeCenter;
        // 文字居中
        self.titleLabel.textAlignment = NSTextAlignmentCenter;
      
    }
    return self;
}