self.navigationItem.titleView不居中

为什么self.navigationItem.titleView有时候不能居中呢

答一：UINavigationBar automatically centers its titleView as long as there is enough room. If the title isn’t centered that means that the title view is too wide to be centered, and if you set the backgroundColor if your UIImageView you’ll see that’s exactly what is happening.

The title view is too wide because that navigation bar will automatically resize the title to hold its content, using -sizeThatFits:. This means that your title view will always be resized to the size of your image.

答二：Sometime inbetween inbetween your view controller’s viewWillAppear: & viewDidAppear:, the navigation bar is repositioning your titleView and resizing it to fit if necessary. It can end up uncentered because the navigation bar is prefering not to resize your titleView to fit between the buttons. It seems to try to center the title view if it’s small enough, but if not will move your titleView off-center, and then I think only as last resort will resize. The effect is that the titleView is taking up all the space between the two buttons, if its textAlignment is centered then it will centered in that space though not the centered with respect to the whole screen. You can see this in your screen shot.

怎么让它居中呢
值得注意的是如果你的titleView是Label什么的 TextAlignment应该设成center 使用sizetofit

答一

It’s possible to start with the titleView being the screen width, then after the navigation bar changes titleView.frame, update it again yourself in the view controller’s viewDidAppear:. Using its adjusted titleView.frame.origin.x and size.width along with the screen width, you can calculate the largest of the left & right margins, then set the origin.x to that, the size.width to the screen width minus that times 2. However that doesn’t take effect until after the pushed view has animated in and the shift afterwards is visible. You could hide the titleView in viewWillAppear: then unhide in viewDidAppear: after centering it, so instead of sliding in with an off-center titleView which is then shifted, it would slide in with no title which then appears.

A better possibility is to make your titleView your own subclass of UIView (or UILabel or whichever) and override setFrame to resize itself to stay centered in its superview. If I ever end up doing this myself I’ll post it here. Or maybe someone else knows another place to change the titleView’s frame after its been updated but before the view slides in without a view subclass.

这种方法我自己亲测可用 CustomView中重写setframe方法 self.navigationItem.titleView = customView

[objc] view plain copy 在CODE上查看代码片派生到我的代码片
- (void)setFrame:(CGRect)frame
{
[super setFrame:frame];
self.center = CGPointMake(self.superview.center.x, self.center.y);
}

答二：Just add your image to navigationController.navigationBar

CGRect myImageS = CGRectMake(0, 0, 44, 44);
UIImageView *logo = [[UIImageView alloc] initWithFrame:myImageS];
[logo setImage:[UIImage imageNamed:@”color.png”]];
logo.contentMode = UIViewContentModeScaleAspectFit;
logo.center = CGPointMake(self.navigationController.navigationBar.width / 2.0, self.navigationController.navigationBar.height / 2.0);
logo.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleBottomMargin;
[self.navigationController.navigationBar addSubview:logo];

http://blog.youkuaiyun.com/wsxzk123/article/details/44755787