Question

我试图让这段代码工作，但似乎无法获得任何显示变量设置的输出：

#import <Foundation/Foundation.h>
#import "thingy.h"

int main (int argc, const char * argv[])
{

@autoreleasepool {

thingy *mythingy;

    [mythingy setMass:75.00];
    [mythingy setTime:5.00];

    NSLog(@"mass of mythingy = %f kg", [mythingy mass]);
    NSLog(@"time of mythingy = %f sec", [mythingy time]);

    }
return 0;
}

这是我得到的输出：

mass of mythingy = 0.000000 kg
time of mythingy = 0.000000 sec

我也尝试过不使用@autoreleasepool（ARC），代码如下所示，但输出与以前相同：

NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    thingy *mythingy;

    [mythingy setMass:75.00];
    [mythingy setTime:5.00];

    NSLog(@"mass of mythingy = %f kg", [mythingy mass]);
    NSLog(@"time of mythingy = %f sec", [mythingy time]);

[mythingy release];
[pool drain];

更新：

好吧所以我采用了之前的代码，并添加了一行，它现在看起来像这样但工作但令人沮丧，因为我想使用ARC !!!!

NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
thingy *mythingy = [[thingy alloc]init];

    [mythingy setMass:75.00];
    [mythingy setTime:5.00];

    NSLog(@"mass of mythingy = %f kg", [mythingy mass]);
    NSLog(@"time of mythingy = %f sec", [mythingy time]);

[mythingy release];
[pool drain];

此代码的输出：

mass of mythingy = 75.000000 kg
time of mythingy = 5.000000 sec

Answer 1

您必须先创建一个对象（mythingy）才能使用它。尝试将thingy *mythingy;更改为thingy *mythingy = [mythingy new];或使用自定义方法对其进行初始化。

Answer 2

你在哪里分配东西？
你需要像

这样的东西

mythingy = [[thingy alloc] init];
// or
mythingy = [thingy new];

Objective-C无法设置类/对象变量

2 个答案: