iOS中OC的动态运行方法

为什么说OC是一个动态运行的语言，是因为runtime的设计， 让oc在运行过程中也可以改变执行方法，让我们的编程更加灵活。我们可以通过字符串的形式去调用方法或者属性。

方法调用01

- (void)viewDidLoad {
    [super viewDidLoad];
    
    SEL sel = NSSelectorFromString(@"animalRun:andDogName:");
    NSString *result = [self performSelector:sel withObject:@"huahua" withObject:@"doudou"];
    NSLog(@"%@", result);
}

- (NSString *)animalRun:(NSString *)catName andDogName:(NSString *)dogName{
    return [NSString stringWithFormat:@"We begin running, %@, %@", catName, dogName];
}

NSSelector和NSString之间的互换

NSString *funcName = NSStringFromSelector(sel);
SEL sel = NSSelectorFromString(@"animalRun:andDogName:");

方法调用方式02

通过NSInvocation的方式

   NSMethodSignature *sign = [[self class] instanceMethodSignatureForSelector:@selector(animalRun:dogName:chickenName:)];
//  注意：生成NSMethodSignature 时有两个方法， 类方法选择methodSignatureForSelector， 实例方法选择：instanceMethodSignatureForSelector 不要搞错了。
//  NSMethodSignature *sign = [NSMethodSignature methodSignatureForSelector:@selector(animalRun:dogName:chickenName:)];
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:sign];
    NSString *catName = @"hua hua";
    NSString *dogName = @"dou dou";
    NSString *chickenName = @"wu shi";
    [invocation setArgument:&catName atIndex:2];
    [invocation setArgument:&dogName atIndex:3];
    [invocation setArgument:&chickenName atIndex:4];
    invocation.selector = @selector(animalRun:dogName:chickenName:);
    [invocation invokeWithTarget:self];
    //  涉及到C & OC的交互，不写__unsafe_unretained 会导致崩溃， 原因是c语言赋值，
    //  不会对returnValue02进行retainCount+1的操作， 导致returnValue02被多次释放导致崩溃。
    //  __unsafe_unretained表示这个类型不安全，不要再释放。
    NSString __unsafe_unretained * returnValue02 = nil;
    [invocation getReturnValue:&returnValue02];
    NSLog(@"%@", returnValue02);

- (NSString *)animalRun:(NSString *)catName dogName:(NSString *)dogName chickenName:(NSString *)chickenName{
    return [NSString stringWithFormat:@"We begin running, %@, %@, %@", catName, dogName, chickenName];
}

方法调用方式03

转换成C语言的调用方式

- (void)viewDidLoad {
    [super viewDidLoad];

    NSString *funcName = NSStringFromSelector(sel);
    SEL animalSel = NSSelectorFromString(@"animalRun:");
    IMP imp = [self methodForSelector:animalSel];
    NSString * (*func)(id, SEL, id) = (void *)imp;

    NSString *result01 = func(self, sel, @[@"hua hua", @"dou dou"]);
    NSLog(@"%@", result01);
}

- (NSString *)animalRun:(NSArray *)animals{
    NSString *animalsString = [animals componentsJoinedByString:@"&"];
    return [NSString stringWithFormat:@"Animals runing:%@", animalsString];
}

方法调用方式04

直接通过objc_msgSend方法调用

    // 注意引入头文件， 否则有警告 #import <objc/message.h>
    NSString * (*action)(id, SEL, NSString *, NSString *, NSString *) = (NSString * (*)(id, SEL, NSString *, NSString *, NSString *)) objc_msgSend;
    result = action(self, @selector(animalRun:dogName:chickenName:), catName, dogName, chickenName);
    NSLog(@"%@", result);

属性

    self.userName = @"Jack";
    NSString *userName = [self valueForKey:@"userName"];
    NSLog(@"%@", userName);
    [self setValue:@"Bruce" forKey:@"userName"];
    NSLog(@"%@", self.userName);

其它

    // 第一个参数：给哪个对象添加关联
    // 第二个参数：关联的key，通过这个key获取
    // 第三个参数：关联的value
    // 第四个参数:关联的策略
    objc_setAssociatedObject(self, key, name, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

    NSClassFromString(@"__NSCFString")

    Class toolClass = object_getClass([tool class]);

    class_getInstanceMethod
    method_exchangeImplementations
    ....
   //等等

PS：祝大家好运