1. 概述

本文要实现的是在iOS上点击输入框后，如果输入框在键盘之下，那么将自动移动界面使得输入框在键盘之上！就像Android的效果那样。效果图如下：

show.gif

2. 一分钟实现该效果：

1. 点击这里下载 WPAutoSpringTextViewController.h, WPAutoSpringTextViewController.m, UIResponder+FirstResponder.h, UIResponder+FirstResponder.m四个文件到你的工程中
2. 修改你的ViewController的父类为WPAutoSpringTextViewController

大功告成，是不是很简单！如果想了解实现方法，请继续阅读。

3. 实现原理

首先，我们需要监听键盘的广播：

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

键盘弹出广播中我们需要获取键盘弹出的高度，键盘弹出的时间。

float duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] floatValue];
CGFloat keyboardHeight = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue].size.height;

然后我们判断此时view需要移动的距离，这里首先获取firstResponder，然后判断其是否为UITextView或UITextField类或其子类，再根据该输入框在屏幕上的位置计算是否需要弹起view，需要则返回需要弹起的高度，不需要则为0。

- (CGFloat)shouldScrollWithKeyboardHeight:(CGFloat)keyboardHeight{
    id responder = [UIResponder currentFirstResponder];
    if([responder isKindOfClass:[UITextView class]] || [responder isKindOfClass:[UITextField class]]){
        UIView *view = responder;
        CGFloat y = [responder convertPoint:CGPointZero toView:[UIApplication sharedApplication].keyWindow].y;
        CGFloat bottom = y + view.frame.size.height;
        if(bottom > SCREEN_HEIGHT - keyboardHeight){
            return bottom - (SCREEN_HEIGHT - keyboardHeight);
        }
    }
    return 0;
}

最后当我们发现需要弹起页面时则动画弹起页面：

CGFloat shouldScrollHeight = [self shouldScrollWithKeyboardHeight:keyboardHeight];
    if(shouldScrollHeight == 0){
        return;
    }
    __weak WPAutoSpringTextViewController *weakSelf = self;
    [UIView animateWithDuration:duration animations:^{
        CGRect bounds = weakSelf.view.bounds;
        weakSelf.view.bounds = CGRectMake(0, shouldScrollHeight + 10, bounds.size.width, bounds.size.height);
    }];

这里主要的逻辑都已经完成了，点击在键盘覆盖范围内的输入框时，界面可以自动弹起。当点击空白区域时，键盘自动收起，这个功能代码如下：

self.view.userInteractionEnabled = YES;
[self.view addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewClicked)]];

- (void)viewClicked{
    if(keyboardIsShowing){
        id responder = [UIResponder currentFirstResponder];
        if([responder isKindOfClass:[UITextView class]] || [responder isKindOfClass:[UITextField class]]){
            UIView *view = responder;
            [view resignFirstResponder];
        }
    }
}

好了大功告成！ 完整的代码如下。Github地址
https://github.com/MRsummer/WPAutoSpringKeyboard

#import "WPAutoSpringTextViewController.h"
#import "UIResponder+FirstResponder.h"

#define SCREEN_HEIGHT [UIScreen mainScreen].bounds.size.height

@implementation WPAutoSpringTextViewController{
    BOOL keyboardIsShowing;
}

-(void)viewDidLoad{
    [super viewDidLoad];
    [self enableEditTextScroll];
    self.view.userInteractionEnabled = YES;
    [self.view addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewClicked)]];
}

- (void)viewClicked{
    if(keyboardIsShowing){
        id responder = [UIResponder currentFirstResponder];
        if([responder isKindOfClass:[UITextView class]] || [responder isKindOfClass:[UITextField class]]){
            UIView *view = responder;
            [view resignFirstResponder];
        }
    }
}

- (CGFloat)shouldScrollWithKeyboardHeight:(CGFloat)keyboardHeight{
    id responder = [UIResponder currentFirstResponder];
    if([responder isKindOfClass:[UITextView class]] || [responder isKindOfClass:[UITextField class]]){
        UIView *view = responder;
        CGFloat y = [responder convertPoint:CGPointZero toView:[UIApplication sharedApplication].keyWindow].y;
        CGFloat bottom = y + view.frame.size.height;
        NSLog(@"shouldScrollWithKeyboardHeight -->keyboradHeight %@, keyboradBottom %@, viewY %@, bottom %@", @(keyboardHeight), @(SCREEN_HEIGHT - keyboardHeight), @(y), @(bottom));
        if(bottom > SCREEN_HEIGHT - keyboardHeight){
            return bottom - (SCREEN_HEIGHT - keyboardHeight);
        }
    }
    return 0;
}

- (void)enableEditTextScroll{
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(wpKeyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(wpKeyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(wpKeyboardDidShow) name:UIKeyboardDidShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(wpKeyboardDidHide) name:UIKeyboardDidHideNotification object:nil];
}

- (void)wpKeyboardDidShow{
    keyboardIsShowing = YES;
}

- (void)wpKeyboardDidHide{
    keyboardIsShowing = NO;
}

- (void)wpKeyboardWillHide:(NSNotification *)note {
    float duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] floatValue];
    __weak WPAutoSpringTextViewController *weakSelf = self;
    [UIView animateWithDuration:duration animations:^{
        CGRect bounds = weakSelf.view.bounds;
        weakSelf.view.bounds = CGRectMake(0, 0, bounds.size.width, bounds.size.height);
    }];
}

- (void)wpKeyboardWillShow:(NSNotification *)note {
    float duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] floatValue];
    CGFloat keyboardHeight = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue].size.height;
    CGFloat shouldScrollHeight = [self shouldScrollWithKeyboardHeight:keyboardHeight];
    if(shouldScrollHeight == 0){
        return;
    }
    __weak WPAutoSpringTextViewController *weakSelf = self;
    [UIView animateWithDuration:duration animations:^{
        CGRect bounds = weakSelf.view.bounds;
        weakSelf.view.bounds = CGRectMake(0, shouldScrollHeight + 10, bounds.size.width, bounds.size.height);
    }];
}

@end