NSClassFromString 和 遍历UIView获取她所在的UIViewController的tips

一、NSClassFromString是NSObjCRuntime.h的方法

FOUNDATION_EXPORT Class __nullable NSClassFromString(NSString *aClassName);

Description：Obtains a class by name.The name of a class.Parameters：aClassName  The name of a classReturns：The class object named by aClassName , or nil if no class by that name is currently loaded

通过NSClassFromString创建类,可以使用里氏代换原则区创建子类

假设有一个类名为：DBHelper

一般创建她的Instance：

[[DBHelper alloc] init];

但是如果用NSClassFromString创建实体的话：

NSString * className = @"DBHelper";
Class class = NSClassFromString(className);
if (class)
{
      DBHelper * dbHelper = class.new;
}

或者：

NSString * className = @"DBHelper";
id dbHelperObj = [[NSClassFromString(className) alloc] init];

这样写很明显的好处：

1.使用的时候，不必担心因为类不存在而报错，因为返回空的时候是nil，所以不会导致程序崩溃

2.方便使用里氏代换原则的模式

二、在自定义的UIView(hex)的控件类里面，如何获取她所在当前的UIViewController的小技巧

1.首先，确保你创建的类继承自UIView

2.其次，我们都知道大部分的UIKit类继承自UIResponder。

啥是UIResponder？

UIResponder中有很多我们耳熟能详的几种方法：

1》nextResponder

- (UIResponder * _Nullable)nextResponder
Description：
Returns the receiver'€™s next responder, or nil if it has none.
The next object in the responder chain to be presented with an event for handling.
Returns：
The next object in the responder chain to be presented with an event for handling.

2》响应链中的操作

- (BOOL)canBecomeFirstResponder;    // default is NO
- (BOOL)becomeFirstResponder;

- (BOOL)canResignFirstResponder;    // default is YES
- (BOOL)resignFirstResponder;

- (BOOL)isFirstResponder;

3》touch事件

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesCancelled:(nullable NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesEstimatedPropertiesUpdated:(NSSet * _Nonnull)touches NS_AVAILABLE_IOS(9_1);

etc.

3.所以我们用到UIResponder中nextResponder方法

for(UIView * view = self; view; view = view.superview)
{
       UIResponder * nextResponder = [view nextResponder];
       if  ([nextResponder iskindOfClass:[UIViewController class]])
       {
             return (UIViewController *)nextResponder;
       }
}

其实，还有回到跟视图的方法，你们可以试试写出来