iOS 实现输入框跟随键盘自动上移

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0.2 2017.04.12 18:15* 字数 937

场景还原

有些时候在包含输入框的页面中,点击输入框输入会因键盘弹起而遮挡住一部分输入框,影响用户体验。iOS在默认情况下并不会处理这种问题,不过我们可以自己实现键盘弹起输入框自动上移的效果。

测试页面

实现思路

观察键盘的弹起与收回,当弹起的键盘会遮挡住输入框时,将输入框跟随键盘一并上移合适的距离,当键盘收回时,输入框回到原始状态。

具体方案

1. 注册两个观察者,观察键盘的弹起与收回

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

2. 在上面的keyboardWillShow和keyboardWillHide方法中分别实现输入框的上移和还原

  • 上移
    当弹起的键盘遮住了页面上的输入框时,我们应该将输入框移至键盘之上,而键盘没有遮到输入框时,并不需要操作。因此在ios的坐标系下,我们可以分别获取键盘弹起后上端的Y坐标和输入框下端的Y坐标,通过做差可以判断出键盘是否遮住了输入框。上移我们可以采用view的transform属性进行平移变换,而不是直接去操作view的frame,这样做的好处是当我们要还原view的状态时可以直接将transform重置为0,而不需要再关心计算下移时的距离。
  • 还原(下移至原始状态)
    根据前面所说,我们只要在恰当的时机操作view的transform属性就可以实现了。
- (void)keyboardWillShow:(NSNotification *)notification
{
    //获取处于焦点中的view
    NSArray *textFields = @[phoneNemberText, verifyCodeText];
    UIView *focusView = nil;
    for (UITextField *view in textFields) {
        if ([view isFirstResponder]) {
            focusView = view;
            break;
        }
    }
    if (focusView) {
        //获取键盘弹出的时间
        double duration = [notification.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
        //获取键盘上端Y坐标
        CGFloat keyboardY = [userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue].origin.y;
        //获取输入框下端相对于window的Y坐标
        CGRect rect = [focusView convertRect:focusView.bounds toView:[[[UIApplication sharedApplication] delegate] window]];
        CGPoint tmp = rect.origin;
        CGFloat inputBoxY = tmp.y + focusView.frame.size.height;
        //计算二者差值
        CGFloat ty = keyboardY - inputBoxY;
        NSLog(@"position keyboard: %f, inputbox: %f, ty: %f", keyboardY, inputBoxY, ty);
        //差值小于0,做平移变换
        [UIView animateWithDuration:duration animations:^{
            if (ty < 0) {
                self.view.transform = CGAffineTransformMakeTranslation(0, ty);
            }
        }];
    }
}
 
- (void)keyboardWillHide:(NSNotification *)notification
{
    //获取键盘弹出的时间
    double duration = [notification.userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];
    //还原
    [UIView animateWithDuration:duration animations:^{
        self.view.transform = CGAffineTransformMakeTranslation(0, 0);
    }];
}

看上去这样已经完美实现了输入框随键盘自动上移,我们也可以喝杯茶稍微休息一下了。没错,在iOS 8及之后的系统中,确实可以正常的工作,然而如果你的应用需要适配iOS 7并且要支持横屏,那么上面的方式在iOS7上,并不能按照我们的期望正确移动。
原因:在ios7上,键盘的frame,系统是按照竖屏状态下window坐标系来计算的,并不考虑旋转的因素,因此在横屏下得到的键盘frame是错误的。受此影响的还有横屏时获取屏幕宽高[UIScreen mainScreen].bounds,也会有这样的问题。这种情况我们不仅无法正确得到键盘的frame,而且输入框相对于window的坐标计算结果也是错误的。
因此在ios7上,键盘上端的Y坐标以及输入框下端相对于window的Y坐标需要单独处理。键盘上端的Y坐标可以通过屏幕高度减键盘高度得到。我们通过下面的方法获取键盘上端的Y坐标。

- (CGFloat)getKeyboardY:(NSDictionary *)userInfo
{
    CGFloat screenHeight;
    CGFloat keyboardY = 0;
    CGFloat keyboardHeight = 0;
    UIInterfaceOrientation orientation = [UIApplication sharedApplication].statusBarOrientation;
    if (( [[[UIDevice currentDevice] systemVersion] floatValue]<8)  && UIInterfaceOrientationIsLandscape(orientation))
    {
        screenHeight = [[UIScreen mainScreen] bounds].size.width;
        keyboardHeight = [userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue].size.width;
        keyboardY = screenHeight - keyboardHeight;
    }
    else if (( [[[UIDevice currentDevice] systemVersion] floatValue]<8)  && UIInterfaceOrientationIsPortrait(orientation)) {
        screenHeight = [[UIScreen mainScreen] bounds].size.height;
        keyboardHeight = [userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue].size.height;
        keyboardY = screenHeight - keyboardHeight;
    }
    else {
        keyboardY = [userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue].origin.y;
    }
    return keyboardY;
}

输入框下端相对于window的坐标如何计算呢?我们首先获得的其实是基于竖屏状态下坐标系中的Y值,而我们期望的是横屏下得到横屏状态下坐标系中的Y值,根据两个坐标系的关系,可以将第一次转换得到的坐标再做一次转换,计算得出横屏坐标系下的Y坐标值。我们通过下面的方法获取输入框下端的Y坐标。

- (CGPoint)getViewOriginPointToWindow:(UIView *)view
{
    CGPoint origin;
    if ([[[UIDevice currentDevice] systemVersion] floatValue] < 8) {
        CGPoint focusViewPoint = [view convertPoint:CGPointZero toView:nil];
        UIInterfaceOrientation orientation = [UIApplication sharedApplication].statusBarOrientation;
        if (orientation == UIInterfaceOrientationLandscapeLeft) {
            origin.y = focusViewPoint.x;
            origin.x = [[[UIApplication sharedApplication] delegate] window].bounds.size.height - focusViewPoint.y;
        }
        else if (orientation == UIInterfaceOrientationLandscapeRight) {
            origin.y = [[[UIApplication sharedApplication] delegate] window].bounds.size.width - focusViewPoint.x;
            origin.x = focusViewPoint.y;
        }
        else if (orientation == UIInterfaceOrientationPortraitUpsideDown) {
            origin.y = [[[UIApplication sharedApplication] delegate] window].bounds.size.height - focusViewPoint.y;
            origin.x = [[[UIApplication sharedApplication] delegate] window].bounds.size.width - focusViewPoint.x;
        }
        else {
            origin = focusViewPoint;
        }
    }
    else {
        CGRect rect = [view convertRect:view.bounds toView:[[[UIApplication sharedApplication] delegate] window]];
        origin = rect.origin;
    }
    return origin;
}

因此我们将之前获取两个Y坐标的代码改用下面的方式:

//获取键盘上端Y坐标
CGFloat keyboardY = [self getKeyboardY:notification.userInfo];
//获取输入框下端相对于window的Y坐标
CGPoint tmp = [self getViewOriginPointToWindow:focusView];
CGFloat inputBoxY = tmp.y + focusView.frame.size.height;

这样就完美实现了输入框随键盘自动上移的效果。

测试页面
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