Updating a xib view's position after a uiviewcontroller loads?

问题

I have a simple UIViewController which has a corresponding .xib file.

ViewController *v = [[ViewController alloc] initWithNibName:@"ViewController" bundle:[NSBundle mainBundle]];
[self.navigationController pushViewController:v animated:YES];

In this .xib file, I have a UILabel, which is positioned in the middle of the screen. I would like to move this label to a new position once the view is loaded, but before it is visible:

label.center = CGPointMake(0,0);

When I try putting the above code in the following methods, this is what happens:

initWithNibName:bundle: position doesn't update
awakeFromNib: position doesn't update
viewDidLoad: position doesn't update
viewWillAppear: position doesn't update
viewDidAppear: position only updates after the view is fully loaded (i.e. the label's original position can be seen for a split second).

When I try updating something like the text property:

label.text = @"Foo";

... it works in all of these methods. For some reason, it is only the position that gets overridden by the .xib file.

When I say that "position doesn't update" I mean that when the label is shown on the screen, it is in the location defined in the .xib file rather than the one I am trying to override it with.

When I try to NSLog the position, it shows that it updates it correctly, but then when I check the position again in viewDidAppear, it shows the incorrect value. For example, say the .xib defines the x at 99, and I want to change it to 0:

- (void)viewWillAppear:(BOOL)animated {
    label.center = CGPointMake(0,0);
    NSLog(@"%f", label.center.x); // reports 0
}

- (void)viewDidAppear:(BOOL)animated {
    NSLog(@"%f", label.center.x); // reports 99 (Error: should be 0)
    label.center = resultLabelHiddenCenter;
    NSLog(@"%f", label.center.x); // reports 0
}

How can I update the label's center before the view is shown without any visual glitches?

回答1:

I think , You are using autoLayout for your xib.

I have two solutions for you in my mind.

First one is , please don't use setFrame or setBounds because Autolayout will skip them.

Changing the constraints is the best solution .You can also add/remove extra constraints.

A good video tutorial is available in WWDC 2012 regarding Autolayout adjustments.

Second one is,Implement viewDidLayoutSubviews which will call just after the view controller's view's layoutSubviews method is invoked.

- (void)viewDidLayoutSubviews
{
    @try
    {
         // reset label frame here.
    }
    @catch (NSException *exception)
    {
        NSLog(@"%s\n exception: Name- %@ Reason->%@", __PRETTY_FUNCTION__,[exception name],[exception reason]);
    }
}

来源：https://stackoverflow.com/questions/15458174/updating-a-xib-views-position-after-a-uiviewcontroller-loads

标签

ios

uiviewcontroller