动态创建类

• 对应的常用API

动态创建一个类（参数：父类，类名，额外的内存空间）
Class objc_allocateClassPair(Class superclass, const char *name, size_t extraBytes)

注册一个类（要在类注册之前添加成员变量）
void objc_registerClassPair(Class cls) 

销毁一个类
void objc_disposeClassPair(Class cls)

获取isa指向的Class
Class object_getClass(id obj)

设置isa指向的Class
Class object_setClass(id obj, Class cls)

判断一个OC对象是否为Class
BOOL object_isClass(id obj)

判断一个Class是否为元类
BOOL class_isMetaClass(Class cls)

获取父类
Class class_getSuperclass(Class cls)

• 动态添加类举例

// 创建类
    Class newClass = objc_allocateClassPair([NSObject class], "Dog", 0);
    class_addIvar(newClass, "_age", 4, 1, @encode(int));
    class_addIvar(newClass, "_weight", 4, 1, @encode(int));
    class_addMethod(newClass, @selector(run), (IMP)run, "v@:");
    // 注册类
    objc_registerClassPair(newClass);
    

    id dog = [[newClass alloc] init];
    [dog setValue:@10 forKey:@"_age"];
    [dog setValue:@20 forKey:@"_weight"];
    [dog run];

    NSLog(@"%@ %@", [dog valueForKey:@"_age"], [dog valueForKey:@"_weight"]);
    
    // 在不需要这个类时释放
    objc_disposeClassPair(newClass);

实例变量

• 对应的常用API

获取一个实例变量信息
Ivar class_getInstanceVariable(Class cls, const char *name)

拷贝实例变量列表（最后需要调用free释放）
Ivar *class_copyIvarList(Class cls, unsigned int *outCount)

设置和获取成员变量的值
void object_setIvar(id obj, Ivar ivar, id value)
id object_getIvar(id obj, Ivar ivar)

动态添加成员变量（已经注册的类是不能动态添加成员变量的）
BOOL class_addIvar(Class cls, const char * name, size_t size, uint8_t alignment, const char * types)

获取成员变量的相关信息
const char *ivar_getName(Ivar v)
const char *ivar_getTypeEncoding(Ivar v)

例子：

// 获取成员变量信息
    Ivar ageIvar = class_getInstanceVariable([Person class], "_age");
    NSLog(@"%s %s", ivar_getName(ageIvar), ivar_getTypeEncoding(ageIvar));

    //设置和获取成员变量的值
    Ivar nameIvar = class_getInstanceVariable([Person class], "_name");

    Person *person = [[Person alloc] init];
    object_setIvar(person, nameIvar, @"123");
    object_setIvar(person, ageIvar, (__bridge id)(void *)10);
    NSLog(@"%@ %d", person.name, person.age);
    
    // 成员变量的数量
    unsigned int count;
    Ivar *ivars = class_copyIvarList([Person class], &count);
    for (int i = 0; i < count; i++) {
        // 取出i位置的成员变量
        Ivar ivar = ivars[i];
        NSLog(@"%s %s", ivar_getName(ivar), ivar_getTypeEncoding(ivar));
    }
    free(ivars);

实战：修改textField的placeholder 字体颜色

• 取出所有成员变量

unsigned int count;
    Ivar *ivars = class_copyIvarList([UITextField class], &count);
    for (int i = 0; i < count; i++) {
        // 取出i位置的成员变量
        Ivar ivar = ivars[i];
        NSLog(@"%s %s", ivar_getName(ivar), ivar_getTypeEncoding(ivar));
    }
    free(ivars);

• 查找对应的对象 设置值

    UILabel *placeholderLabel = [self.textField valueForKeyPath:@"_placeholderLabel"];
    placeholderLabel.textColor = [UIColor redColor];
  
或者
   [self.textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];

字典转模型

+ (instancetype)wd_objectWithJson:(NSDictionary *)json
{
    id obj = [[self alloc] init];
    
    unsigned int count;
    Ivar *ivars = class_copyIvarList(self, &count);
    for (int i = 0; i < count; i++) {
        // 取出i位置的成员变量
        Ivar ivar = ivars[i];
        NSMutableString *name = [NSMutableString stringWithUTF8String:ivar_getName(ivar)];
        [name deleteCharactersInRange:NSMakeRange(0, 1)];
        
        // 设值
        id value = json[name];
        [obj setValue:value forKey:name];
    }
    free(ivars);
    
    return obj;
}

@end

// 字典转模型
        NSDictionary *json = @{
                               @"id" : @20,
                               @"age" : @20,
                               @"weight" : @60,
                               @"name" : @"Jack"
                               @"no" : @30
                               };
        
        Person *person = [Person wd_objectWithJson:json];

获取属性

获取一个属性
objc_property_t class_getProperty(Class cls, const char *name)

拷贝属性列表（最后需要调用free释放）
objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)

动态添加属性
BOOL class_addProperty(Class cls, const char *name, const objc_property_attribute_t *attributes,
                  unsigned int attributeCount)

动态替换属性
void class_replaceProperty(Class cls, const char *name, const objc_property_attribute_t *attributes,
                      unsigned int attributeCount)

获取属性的一些信息
const char *property_getName(objc_property_t property)
const char *property_getAttributes(objc_property_t property)

动态替换方法

获得一个实例方法、类方法
Method class_getInstanceMethod(Class cls, SEL name)
Method class_getClassMethod(Class cls, SEL name)

方法实现相关操作
IMP class_getMethodImplementation(Class cls, SEL name) 
IMP method_setImplementation(Method m, IMP imp)
void method_exchangeImplementations(Method m1, Method m2) 

拷贝方法列表（最后需要调用free释放）
Method *class_copyMethodList(Class cls, unsigned int *outCount)

动态添加方法
BOOL class_addMethod(Class cls, SEL name, IMP imp, const char *types)

动态替换方法
IMP class_replaceMethod(Class cls, SEL name, IMP imp, const char *types)

获取方法的相关信息（带有copy的需要调用free去释放）
SEL method_getName(Method m)
IMP method_getImplementation(Method m)
const char *method_getTypeEncoding(Method m)
unsigned int method_getNumberOfArguments(Method m)
char *method_copyReturnType(Method m)
char *method_copyArgumentType(Method m, unsigned int index)



选择器相关
const char *sel_getName(SEL sel)
SEL sel_registerName(const char *str)

用block作为方法实现
IMP imp_implementationWithBlock(id block)
id imp_getBlock(IMP anImp)
BOOL imp_removeBlock(IMP anImp)

实战

监听拦截所有的点击事件

@implementation UIControl (Extension)

+ (void)load
{
    // hook：钩子函数
    Method method1 = class_getInstanceMethod(self, @selector(sendAction:to:forEvent:));
    Method method2 = class_getInstanceMethod(self, @selector(wd_sendAction:to:forEvent:));
    method_exchangeImplementations(method1, method2);
}

- (void)wd_sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event
{
    NSLog(@"%@-%@-%@", self, target, NSStringFromSelector(action));
    
    // 调用系统原来的实现
    [self wd_sendAction:action to:target forEvent:event];
    
}

@end

数组添加值时 判 nil 拦截

#import <objc/runtime.h>

@implementation NSMutableArray (Extension)

+ (void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // 类簇：NSString、NSArray、NSDictionary，真实类型是其他类型
        Class cls = NSClassFromString(@"__NSArrayM");
        Method method1 = class_getInstanceMethod(cls, @selector(insertObject:atIndex:));
        Method method2 = class_getInstanceMethod(cls, @selector(wd_insertObject:atIndex:));
        method_exchangeImplementations(method1, method2);
    });
}

- (void)wd_insertObject:(id)anObject atIndex:(NSUInteger)index
{
    if (anObject == nil) return;
    
    [self wd_insertObject:anObject atIndex:index];
}

@end

字典key为nil、值时 判 nil 拦截

#import "NSMutableDictionary+Extension.h"
#import <objc/runtime.h>

@implementation NSMutableDictionary (Extension)

+ (void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class cls = NSClassFromString(@"__NSDictionaryM");
        Method method1 = class_getInstanceMethod(cls, @selector(setObject:forKeyedSubscript:));
        Method method2 = class_getInstanceMethod(cls, @selector(wd_setObject:forKeyedSubscript:));
        method_exchangeImplementations(method1, method2);
        
        Class cls2 = NSClassFromString(@"__NSDictionaryI");
        Method method3 = class_getInstanceMethod(cls2, @selector(objectForKeyedSubscript:));
        Method method4 = class_getInstanceMethod(cls2, @selector(wd_objectForKeyedSubscript:));
        method_exchangeImplementations(method3, method4);
    });
}

- (void)wd_setObject:(id)obj forKeyedSubscript:(id<NSCopying>)key
{
    if (!key) return;
    
    [self wd_setObject:obj forKeyedSubscript:key];
}

- (id)wd_objectForKeyedSubscript:(id)key
{
    if (!key) return nil;
    
    return [self wd_objectForKeyedSubscript:key];
}

@end