如何访问并修改一个类的私有属性？

三种方式供你选择

通过KVC来设置
通过runtime动态改变
通过 msg_send() 设置

先定义这样一个类 PrivateVariablesClass:

#import "PrivateVariablesClass.h"
@interface PrivateVariablesClass ()
@property (nonatomic, assign) NSInteger priviteNum;
@property (nonatomic, strong) UIView *priviteView;
@end
@implementation PrivateVariablesClass
-(void)showPropertyPrivateVariablesClass
{
    NSLog(@"priviteNum = %@", @(_priviteNum));
    NSLog(@"priviteView = %@", _priviteView);
}
@end

我们在外部改完后，调用 showPropertyPrivateVariablesClass 方法去查看这两个私有属性的值。

1.KVC:

-(void)way1{
    PrivateVariablesClass *classA = [[PrivateVariablesClass alloc] init];
    [classA setValue:@(4) forKey:@"_priviteNum"];
    [classA setValue:self.view forKey:@"_priviteView"];
    [classA showPropertyPrivateVariablesClass];
}

结果输出：

priviteNum = 4  
priviteView = <UIView: 0x7fae50f07e10; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x600003c08020>>

2.runtime动态改变

-(void)way2{
    PrivateVariablesClass *classA = [[PrivateVariablesClass alloc] init];
    
    unsigned int outCount = 0;
    Ivar *ivars = class_copyIvarList([PrivateVariablesClass class], &outCount);
    
    for (int i = 0; i < outCount; i ++) {
        Ivar ivar = ivars[i];
        
        const char *ivarName = ivar_getName(ivar);
        
        //这里要注意ARC下， 这个会报错
        /**
         在修改NSInteger型变量的时候，ARC下，编译器不允许你将NSInteger类型的值赋值给id，在buildsetting中将Objective-C Automatic Reference Counting修改为No即可。但是这样工程就会变成MRC，所以，如果是非对象类型就不建议用object_setIvar这样的方法去修改了。
         */
 
        int a = strcmp(ivarName, "_priviteNum");
        if (strcmp(ivarName, "_priviteNum") == 0) {
            //这种方式传值int类型会报错，不能传入
            object_setIvar(classA, ivar, 22);
        }
        
        if (strcmp(ivarName, "_priviteView") == 0) {
            object_setIvar(classA, ivar, self.view);
        }
    }
    
    [classA showPropertyPrivateVariablesClass];
}

结果输出：

priviteNum = 22
priviteView = <UIView: 0x7ffb08e0b040; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x60000398ad40>>

3.msg_send()

既然是私有属性了，必然有setter方法，那我们动态调用一下（适用私有属性，不适用私有变量）。

-(void)way3{
    PrivateVariablesClass *classA = [[PrivateVariablesClass alloc] init];
    ((void (*)(id, SEL, int))(void *) objc_msgSend)((id)classA, @selector(setPriviteNum:) , 33);
    ((void (*)(id, SEL, id))(void *) objc_msgSend)((id)classA, @selector(setPriviteView:) , self.view);
    [classA showPropertyPrivateVariablesClass];
}

结果输出：

priviteNum = 33
priviteView = <UIView: 0x7fd4bfa079f0; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x600001085f40>>

1.KVC:

2.runtime动态改变

3.msg_send()

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