在iOS开发中，使用UIButton设置title和image，达到tabBarItem的效果，即title在下，image在上：
目前，我发现有两种比较好的方法：
方法一，使用UIEdgeInsets
UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
[button setFrame:CGRectMake(100, 100, 60, 60)];
[button setBackgroundColor:[UIColor greenColor]];
UIImage *image = [UIImage imageNamed:@"index"];
[button setTitle:@"首页" forState:UIControlStateNormal];
[button setImage:image forState:UIControlStateNormal];
// 如果不设置，则默认image在左，title在右，居中显示
// 如果如下设置，则title和image重叠居中显示
button.titleEdgeInsets = UIEdgeInsetsMake(0.0, -image.size.width, 0.0, 0.0);
button.imageEdgeInsets = UIEdgeInsetsMake(0.0, 0.0, 0.0, -
button.titleLabel.bounds.size.width);
// 如果如下设置，则title向下移动40个单位，在下，image向上移动20个单位，在上，居中显示
button.titleEdgeInsets = UIEdgeInsetsMake(40.0, -image.size.width, 0.0, 0.0);
button.imageEdgeInsets = UIEdgeInsetsMake(-20.0, 0.0, 0.0, -
button.titleLabel.bounds.size.width);
[self.view addSubview:button];
方法二，重写UIButton的layoutSubviews
- (void)layoutSubviews
{
[super layoutSubviews];
CGPoint center = self.imageView.center;
center.x = self.frame.size.width/2;
center.y = self.imageView.frame.size.height/2;
self.imageView.center = center;
CGRect frame = [self titleLabel].frame;
frame.origin.x = 0;
frame.origin.y = self.imageView.frame.size.height + 2;
frame.size.width = self.frame.size.width;
self.titleLabel.frame = frame;
self.titleLabel.textAlignment = NSTextAlignmentCenter;
[self.titleLabel setFont:[UIFont systemFontOfSize:10.0f]];
}