解决UITextField在键盘弹出时的上移问题

技术背景

在iOS开发中，当用户点击UITextField进行输入时，键盘会弹出，可能会遮挡住UITextField，影响用户输入体验。因此，需要实现当键盘弹出时，UITextField能够自动上移到可见区域。

实现步骤

不使用UIScrollView的方法

若内容能适配iPhone屏幕，无需使用UIScrollView，可通过移动视图来避免UITextField被键盘遮挡。

1. 注册键盘通知：在viewWillAppear方法中注册UIKeyboardWillShowNotification和UIKeyboardWillHideNotification通知。
2. 实现键盘显示和隐藏的处理方法：在keyboardWillShow和keyboardWillHide方法中，根据键盘的显示和隐藏来移动视图。
3. 处理文本字段开始编辑的事件：在textFieldDidBeginEditing方法中，根据需要移动视图。

使用UIScrollView的方法

若内容无法适配iPhone屏幕，则需要使用UIScrollView。

1. 确保contentSize大于UIScrollView的框架大小：这样UIScrollView才能滚动。
2. 注册键盘通知：在viewDidLoad方法中注册UIKeyboardWillShowNotification和UIKeyboardWillHideNotification通知。
3. 调整UIScrollView的大小和内容偏移量：在keyboardWillShow和keyboardWillHide方法中，根据键盘的显示和隐藏来调整UIScrollView的大小和内容偏移量。

使用第三方库IQKeyboardManager

IQKeyboardManager是一个方便的第三方库，可自动处理键盘和UITextField的问题。

1. 添加依赖：在Podfile中添加pod 'IQKeyboardManager'，然后执行pod install。
2. 启用库：在AppDelegate中启用IQKeyboardManager。

核心代码

不使用UIScrollView的Objective - C代码示例

#define kOFFSET_FOR_KEYBOARD 80.0

-(void)keyboardWillShow {
    if (self.view.frame.origin.y >= 0) {
        [self setViewMovedUp:YES];
    } else if (self.view.frame.origin.y < 0) {
        [self setViewMovedUp:NO];
    }
}

-(void)keyboardWillHide {
    if (self.view.frame.origin.y >= 0) {
        [self setViewMovedUp:YES];
    } else if (self.view.frame.origin.y < 0) {
        [self setViewMovedUp:NO];
    }
}

-(void)textFieldDidBeginEditing:(UITextField *)sender {
    if ([sender isEqual:mailTf]) {
        if  (self.view.frame.origin.y >= 0) {
            [self setViewMovedUp:YES];
        }
    }
}

-(void)setViewMovedUp:(BOOL)movedUp {
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:0.3];

    CGRect rect = self.view.frame;
    if (movedUp) {
        rect.origin.y -= kOFFSET_FOR_KEYBOARD;
        rect.size.height += kOFFSET_FOR_KEYBOARD;
    } else {
        rect.origin.y += kOFFSET_FOR_KEYBOARD;
        rect.size.height -= kOFFSET_FOR_KEYBOARD;
    }
    self.view.frame = rect;
    
    [UIView commitAnimations];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(keyboardWillShow)
                                             name:UIKeyboardWillShowNotification
                                           object:nil];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(keyboardWillHide)
                                             name:UIKeyboardWillHideNotification
                                           object:nil];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                             name:UIKeyboardWillShowNotification
                                           object:nil];

    [[NSNotificationCenter defaultCenter] removeObserver:self
                                             name:UIKeyboardWillHideNotification
                                           object:nil];
}

使用UIScrollView的Objective - C代码示例

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                         selector:@selector(keyboardWillShow:) 
                                             name:UIKeyboardWillShowNotification 
                                           object:self.view.window];
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                         selector:@selector(keyboardWillHide:) 
                                             name:UIKeyboardWillHideNotification 
                                           object:self.view.window];
    keyboardIsShown = NO;
    CGSize scrollContentSize = CGSizeMake(320, 345);
    self.scrollView.contentSize = scrollContentSize;
}

- (void)keyboardWillHide:(NSNotification *)n {
    NSDictionary* userInfo = [n userInfo];
    CGSize keyboardSize = [[userInfo objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue].size;
    
    CGRect viewFrame = self.scrollView.frame;
    viewFrame.size.height += (keyboardSize.height - kTabBarHeight);
    
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationBeginsFromCurrentState:YES];
    [self.scrollView setFrame:viewFrame];
    [UIView commitAnimations];
    
    keyboardIsShown = NO;
}

- (void)keyboardWillShow:(NSNotification *)n {
    if (keyboardIsShown) {
        return;
    }
    
    NSDictionary* userInfo = [n userInfo];
    CGSize keyboardSize = [[userInfo objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue].size;

    CGRect viewFrame = self.scrollView.frame;
    viewFrame.size.height -= (keyboardSize.height - kTabBarHeight);
    
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationBeginsFromCurrentState:YES];
    [self.scrollView setFrame:viewFrame];
    [UIView commitAnimations];
    keyboardIsShown = YES;
}

Swift代码示例

func animateTextField(textField: UITextField, up: Bool) {
    let movementDistance: CGFloat = -130
    let movementDuration: Double = 0.3
    
    var movement:CGFloat = 0
    if up {
        movement = movementDistance
    } else {
        movement = -movementDistance
    }
    
    UIView.animate(withDuration: movementDuration, delay: 0, options: [.beginFromCurrentState]) {
        self.view.frame = self.view.frame.offsetBy(dx: 0, dy: movement)
    }
}

func textFieldDidBeginEditing(_ textField: UITextField) {
    animateTextField(textField: textField, up: true)
}

func textFieldDidEndEditing(_ textField: UITextField) {
    animateTextField(textField: textField, up: false)
}

最佳实践

• 使用第三方库：如IQKeyboardManager，可大大减少代码量，提高开发效率。
• 考虑不同屏幕尺寸和设备方向：确保在各种情况下都能正常工作。
• 使用自动布局：结合自动布局可以更好地适应不同的屏幕尺寸和设备方向。

常见问题

• 滚动异常：若UIScrollView滚动异常，需确保contentSize大于UIScrollView的框架大小。
• 重复调整大小：当键盘已经显示时，再次收到键盘显示通知可能会导致UIScrollView重复调整大小，可使用一个标志位来避免。
• 视图未恢复原位：在文本字段结束编辑时，确保视图能恢复到原来的位置。