Runtime學習與使用（一）：為UITextField添加類目實現被鍵盤遮住後視圖上移,點擊空白回收鍵盤

OC中類目無法直接添加屬性，可以通過runtime實現在類目中添加屬性。在學習的過程中，試著為UITextField添加了一個類目，實現了當TextField被鍵盤遮住時視圖上移的功能，順便也添加了點擊空白回收鍵盤功能。效果預覽使用時不需要一句代碼就可以實現上述功能[github鏈接](https ...

OC中類目無法直接添加屬性，可以通過runtime實現在類目中添加屬性。

在學習的過程中，試著為UITextField添加了一個類目，實現了當TextField被鍵盤遮住時視圖上移的功能，順便也添加了點擊空白回收鍵盤功能。
效果預覽
使用時不需要一句代碼就可以實現上述功能

[github鏈接](https://github.com/a1419430265/CHTTextFieldHealper)

.h文件

 1 //
 2 //  UITextField+CHTPositionChange.h
 3 //  CHTTextFieldHealper
 4 //
 5 //  Created by risenb_mac on 16/8/17.
 6 //  Copyright © 2016年 risenb_mac. All rights reserved.
 7 //
 8 
 9 #import <UIKit/UIKit.h>
10 
11 @interface UITextField (CHTHealper)
12 
13 /**
14  *  是否支持視圖上移
15  */
16 @property (nonatomic, assign) BOOL canMove;
17 /**
18  *  點擊回收鍵盤、移動的視圖，預設是當前控制器的view
19  */
20 @property (nonatomic, strong) UIView *moveView;
21 /**
22  *  textfield底部距離鍵盤頂部的距離
23  */
24 @property (nonatomic, assign) CGFloat heightToKeyboard;
25 
26 @property (nonatomic, assign, readonly) CGFloat keyboardY;
27 @property (nonatomic, assign, readonly) CGFloat keyboardHeight;
28 @property (nonatomic, assign, readonly) CGFloat initialY;
29 @property (nonatomic, assign, readonly) CGFloat totalHeight;
30 @property (nonatomic, strong, readonly) UITapGestureRecognizer *tapGesture;
31 @property (nonatomic, assign, readonly) BOOL hasContentOffset;
32 
33 @end

在.h文件中聲明屬性之後需要在.m中重寫setter，getter方法
首先定義全局key用作關聯唯一標識符

1 static char canMoveKey;
2 static char moveViewKey;

@implementation UITextField (CHTHealper)
@dynamic canMove;
@dynamic moveView;

具體實現

1 - (void)setCanMove:(BOOL)canMove {
2 // 參數意義：關聯對象 ，關聯標識符，關聯屬性值，關聯策略
3     objc_setAssociatedObject(self, &canMoveKey, @(canMove), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
4 }
5 
6 - (BOOL)canMove {
7 // 關聯屬性值為對象類型，需要轉換
8     return [objc_getAssociatedObject(self, &canMoveKey) boolValue];
9 }

想要實現鍵盤遮住TextField後視圖上移，首先應確定TextField是否被鍵盤遮住，需要知道TextField在整個屏幕中的位置

// 此方法可以獲得TextField左上角在當前window中的坐標
[self convertPoint:self.bounds.origin toView:[UIApplication sharedApplication].keyWindow]

還需要知道鍵盤高度，這點需要接受系統通知，但是什麼時候接受通知、註銷通知？
我的思路是在TextField成為第一響應者的時候，為TextField添加通知，但是如果直接重寫becomeFirstResponder方法會覆蓋掉UITextField本身的方法，造成的最明顯的後果就是沒有游標了……為了避免這個問題，我用了runtime另外一個強大的功能，方法交換
為了保證方法交換隻進行一次，使用dispatch_once
為了保證方法交換儘早執行，寫在了load方法中

 1 + (void)load {
 2     static dispatch_once_t onceToken;
 3     dispatch_once(&onceToken, ^{
 4         SEL systemSel = @selector(initWithFrame:);
 5         SEL mySel = @selector(setupInitWithFrame:);
 6         [self exchangeSystemSel:systemSel bySel:mySel];
 7         
 8         SEL systemSel2 = @selector(becomeFirstResponder);
 9         SEL mySel2 = @selector(newBecomeFirstResponder);
10         [self exchangeSystemSel:systemSel2 bySel:mySel2];
11         
12         SEL systemSel3 = @selector(resignFirstResponder);
13         SEL mySel3 = @selector(newResignFirstResponder);
14         [self exchangeSystemSel:systemSel3 bySel:mySel3];
15         
16         SEL systemSel4 = @selector(initWithCoder:);
17         SEL mySel4 = @selector(setupInitWithCoder:);
18         [self exchangeSystemSel:systemSel4 bySel:mySel4];
19     });
20     [super load];
21 }

具體交換步驟

 1 // 交換方法
 2 + (void)exchangeSystemSel:(SEL)systemSel bySel:(SEL)mySel {
 3     Method systemMethod = class_getInstanceMethod([self class], systemSel);
 4     Method myMethod = class_getInstanceMethod([self class], mySel);
 5     //首先動態添加方法，實現是被交換的方法，返回值表示添加成功還是失敗
 6     BOOL isAdd = class_addMethod(self, systemSel, method_getImplementation(myMethod), method_getTypeEncoding(myMethod));
 7     if (isAdd) {
 8         //如果成功，說明類中不存在這個方法的實現
 9         //將被交換方法的實現替換到這個並不存在的實現
10         class_replaceMethod(self, mySel, method_getImplementation(systemMethod), method_getTypeEncoding(systemMethod));
11     }else{
12         //否則，交換兩個方法的實現
13         method_exchangeImplementations(systemMethod, myMethod);
14     }
15 }

在上面我交換了四組方法，兩組init方法，是為了保證無論是代碼創建的還是xib拖得TextField都進行初始化

 1 - (instancetype)setupInitWithCoder:(NSCoder *)aDecoder {
 2     [self setup];
 3     return [self setupInitWithCoder:aDecoder];
 4 }
 5 
 6 - (instancetype)setupInitWithFrame:(CGRect)frame {
 7     [self setup];
 8     return [self setupInitWithFrame:frame];
 9 }
10 
11 - (void)setup {
12     self.heightToKeyboard = 10;
13     self.canMove = YES;
14     self.keyboardY = 0;
15     self.totalHeight = 0;
16     self.tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapAction)];
17 }

在TextField成為第一響應者時，為self添加通知接收，為moveView添加點擊事件（實現點擊空白回收鍵盤），註銷第一響應者時，註銷通知，移除點擊事件

 1 - (BOOL)newBecomeFirstResponder {
 2 // 如果沒有設置moveView 預設為當前控制器的view
 3     if (self.moveView == nil) {
 4         self.moveView = [self viewController].view;
 5     }
 6 // 保證moveView只有一個本TextField的點擊事件
 7     if (![self.moveView.gestureRecognizers containsObject:self.tapGesture]) {
 8         [self.moveView addGestureRecognizer:self.tapGesture];
 9     }
10 // 當重覆點擊當前TextField時（重覆成為第一響應者）或設置為不可移動 不再添加通知
11     if ([self isFirstResponder] || !self.canMove) {
12         return [self newBecomeFirstResponder];
13     }
14     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(showAction:) name:UIKeyboardWillShowNotification object:nil];
15     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(hideAction:) name:UIKeyboardWillHideNotification object:nil];
16     return [self newBecomeFirstResponder];
17 }
18 
19 - (BOOL)newResignFirstResponder {
20 // 確保當前moveView有當前點擊事件，移除
21     if ([self.moveView.gestureRecognizers containsObject:self.tapGesture]) {
22         [self.moveView removeGestureRecognizer:self.tapGesture];
23     }
24     if (!self.canMove) {
25         return [self newResignFirstResponder];
26     }
27     BOOL result = [self newResignFirstResponder];
28     [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
29     [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];
30 // 當另外一個TextField成為第一響應者，當前TextField註銷第一響應者時不會回收鍵盤，手動調用moveView改變方法
31     [self hideKeyBoard:0];
32     return result;
33 }
34 //獲取當前TextField所在controller
35 - (UIViewController *)viewController {
36     UIView *next = self;
37     while (1) {
38         UIResponder *nextResponder = [next nextResponder];
39         if ([nextResponder isKindOfClass:[UIViewController class]]) {
40             return (UIViewController *)nextResponder;
41         }
42         next = next.superview;
43     }
44     return nil;
45 }

接收到彈出鍵盤後調用的方法

 1 - (void)showAction:(NSNotification *)sender {
 2     if (!self.canMove) {
 3         return;
 4     }
 5 // 獲取鍵盤高度以及鍵盤的Y坐標
 6     self.keyboardY = [sender.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue].origin.y;
 7     self.keyboardHeight = [sender.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue].size.height;
 8     [self keyboardDidShow];
 9 }
10 
11 - (void)hideAction:(NSNotification *)sender {
12     if (!self.canMove || self.keyboardY == 0) {
13         return;
14     }
15     [self hideKeyBoard:0.25];
16 }
17 
18 - (void)keyboardDidShow {
19     if (self.keyboardHeight == 0) {
20         return;
21     }
22 // 獲取TextField在window中的Y坐標
23     CGFloat fieldYInWindow = [self convertPoint:self.bounds.origin toView:[UIApplication sharedApplication].keyWindow].y;
24 // 確定是否需要視圖上移，以及移動的距離
25     CGFloat height = (fieldYInWindow + self.heightToKeyboard + self.frame.size.height) - self.keyboardY;
26     CGFloat moveHeight = height > 0 ? height : 0;
27     
28     [UIView animateWithDuration:0.25 animations:^{
29 // 判斷是否是scrollView併進行相應移動
30         if (self.hasContentOffset) {
31             UIScrollView *scrollView = (UIScrollView *)self.moveView;
32             scrollView.contentOffset = CGPointMake(scrollView.contentOffset.x, scrollView.contentOffset.y + moveHeight);
33         } else {
34             CGRect rect = self.moveView.frame;
35             self.initialY = rect.origin.y;
36             rect.origin.y -= moveHeight;
37             self.moveView.frame = rect;
38         }
39 // 記錄當前TextField使得moveView移動的距離
40         self.totalHeight += moveHeight;
41     }];
42 }
43 
44 - (void)hideKeyBoard:(CGFloat)duration {
45     [UIView animateWithDuration:duration animations:^{
46         if (self.hasContentOffset) {
47             UIScrollView *scrollView = (UIScrollView *)self.moveView;
48             scrollView.contentOffset = CGPointMake(scrollView.contentOffset.x, scrollView.contentOffset.y - self.totalHeight);
49         } else {
50             CGRect rect = self.moveView.frame;
51             rect.origin.y += self.totalHeight;
52             self.moveView.frame = rect;
53         }
54 // moveView回覆狀態後將移動距離置0
55         self.totalHeight = 0;
56     }];
57 }

點擊事件當前controllerview endediting

- (void)tapAction {
    [[self viewController].view endEditing:YES];
}