KVC - (void)setValue:(nullable id)value forKey:(NSString *)key;

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关于KVC的方法

- (void)setValue:(nullable id)value forKey:(NSString *)key;

从上面的参数类型可以看出,value必须是一个对象,可以为nil对象.

当你的属性是@property (nonatomic, assign) NSInteger testNum;

则在使用KVC时,必须将其转换成NSNumber对象,或NSString对象.但不能转换成数组等其他对象类型.

[self setValue:@99 forKey:@"testNum"]; //√

[self setValue:@"99" forKey:@"testNum"]; //√

[self setValue:@[@99] forKey:@"testNum"]; //x.程序崩溃,提示:-[__NSArrayI longLongValue]: unrecognized selector sent to instance 0x12750c110

猜测:当属性的类型是基础类型时使用KVC,苹果内部会给传入的value参数发送-longLongValue消息,然后赋值给属性的值.然而NSArray,并没有longLongValue这个方法,于是崩溃.(NSNumber和NSString都有longLongValue方法).

示例:

　 [self setValue:@"99" forKey:@"testNum"];
    NSLog(@"%ld", self.testNum); //这里打印的是99
    self.testNum += 4;
    NSLog(@"%ld", self.testNum);

注意:你声明的属性是什么类型,那么你使用KVC时传入的参数value就应该是对应的类型.否则你使用该属性时,尤其是调用这个属性类型里面的方法时将导致崩溃.

比如:有属性@property (nonatomic, strong) NSString *testStr;

有如下代码:

　 NSArray *sd = @[@"afaf"];
    [self setValue:sd forKey:@"testStr"];
    NSLog(@"%@", self.testStr); //打印:(afaf).打印这个属性的值并不会崩溃.
    NSString *d = self.testStr; //这里也不会崩溃,也没有任何警告.
    NSLog(@"%@",[d class]); //打印:__NSArrayI.说明变量d的类型并不是NSString.
    NSString *gs = [NSString stringWithString:d];  //程序在这一行崩溃.提示-[__NSArrayI length]: unrecognized selector sent to instance 0x15cd2c1d0
    NSLog(@"%@",gs);

另外:

#if __LP64__ || (TARGET_OS_EMBEDDED && !TARGET_OS_IPHONE) || TARGET_OS_WIN32 || NS_BUILD_32_LIKE_64
typedef long NSInteger;
typedef unsigned long NSUInteger;
#else
typedef int NSInteger;
typedef unsigned int NSUInteger;
#endif

对于NSNumber类,它有以下方法

@property (readonly) int intValue;
@property (readonly) unsigned int unsignedIntValue;
@property (readonly) long longValue;
@property (readonly) unsigned long unsignedLongValue;
@property (readonly) long long longLongValue;
@property (readonly) unsigned long long unsignedLongLongValue;

@property (readonly) NSInteger integerValue NS_AVAILABLE(10_5, 2_0);
@property (readonly) NSUInteger unsignedIntegerValue NS_AVAILABLE(10_5, 2_0);

而对于NSString类,它有:

@property (readonly) int intValue;
@property (readonly) NSInteger integerValue NS_AVAILABLE(10_5, 2_0);
@property (readonly) long long longLongValue NS_AVAILABLE(10_5, 2_0);

可以看到,NSString类里面把NSString对象转换成基础类型的方法远比NSNumber类里的要少.所以当你有属性为

@property (nonatomic, assign) NSUInteger testNum;

那么当执行下面的KVC时,将崩溃.提示:-[__NSCFConstantString unsignedLongLongValue]: unrecognized selector sent to instance 0x1001008d0

[self setValue:@"99" forKey:@"testNum"];

而执行self setValue:@99 forKey:@"testNum"];则不会崩溃.

综上,当建模时,如无特别要求,基础数据类型最好设置为NSInteger,或int或者干脆设置为NSString类型.设置为NSUInteger可能会在使用KVC时导致崩溃.特别是在结合JSONModel第三方库使用时.

KVC - (void)setValue:(nullable id)value forKey:(NSString *)key;

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原文地址：http://www.cnblogs.com/xuequan-programmingForiOS/p/5005694.html