ios - Present ViewController 模态显示奇怪的动画

Question

我正在尝试创建一个简单的模态视图 Controller ，让您可以使用 TextView 编辑文本。但是，当我以模态方式呈现 View Controller 时，它会从左下方向滑入，而不是仅从底部滑入。

这是一个奇怪效果的视频:http://youtu.be/9M_MHA5mt1M

我的 Controller 只是观察键盘的显示，然后适本地使用自动布局调整 TextView 的大小。这是代码:

#import "TextPicker.h"

@interface TextPicker ()

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *keyboardHeight;

@end

@implementation TextPicker

- (id)initWithText:(NSString *)text
{
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPhone" bundle:nil];
    self = [storyboard instantiateViewControllerWithIdentifier:@"textPicker"];
    if (self) {
        self.text = text;

    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self observeKeyboard];

    //self.textView.text = self.text;
    [self.textView becomeFirstResponder];
}


- (void) viewWillDisappear:(BOOL)animated {
    [self.textView resignFirstResponder];
}

- (IBAction)savePressed:(id)sender {
    [self dismissViewControllerAnimated:YES completion:nil];    
}

- (IBAction)cancelPressed:(id)sender {
    [self dismissViewControllerAnimated:YES completion:nil];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

- (void) dealloc {
    [self stopObervingKeyboard];
}

- (void)observeKeyboard {
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillChangeFrameNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
}

- (void)stopObervingKeyboard {
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillChangeFrameNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];
}

- (void)keyboardWillShow:(NSNotification *)notification {
    NSDictionary *info = [notification userInfo];

    NSValue *kbFrame = [info objectForKey:UIKeyboardFrameEndUserInfoKey];
    CGRect keyboardFrame = [kbFrame CGRectValue];
    self.keyboardHeight.constant = -keyboardFrame.size.height;

    NSTimeInterval animationDuration = [[info objectForKey:UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    [UIView animateWithDuration:animationDuration animations:^{
        [self.view layoutIfNeeded];
    }];
}

- (void)keyboardWillHide:(NSNotification *)notification {
    NSDictionary *info = [notification userInfo];
    NSTimeInterval animationDuration = [[info objectForKey:UIKeyboardAnimationDurationUserInfoKey] doubleValue];

    self.keyboardHeight.constant = 0;
    [UIView animateWithDuration:animationDuration animations:^{
        [self.view layoutIfNeeded];
    }];
}

- (IBAction)dismissKeyboard:(id)sender {
    [self.textView resignFirstResponder];
}


@end

Answer 1

通过将 [self.view layoutIfNeeded] 调用包装在动画 block 中，您的 View 会按照您的要求进行动画处理。

在 viewDidLoad 中，您开始观察键盘变化，并且当您检测到它们时，您会为调整设置动画，这通常是正确的。但是，在 View 进行第一次布局之前，您需要显示键盘；这会导致所有 View 从 CGRectZero 到适当大小的动画。这就是您看到的效果。

所以基本上您需要让 View 有机会在您的动画 layoutIfNeeded 调用之前进行布局。可能最简单的方法就是将 [self.textView becomeFirstResponder]; 移动到 viewWillAppear: 或 viewDidAppear:。

*作为旁注，记得在出场电话中调用 super。我注意到你没有调用 [super viewWillDisappear];。