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我正在玩一个简单的OCUnit测试用于iPhone应用程序,并且只是想断言应用程序委托是我期望它的类的实例.我没想到这个测试非常有用,但结果却揭示了我对Objective C的误解.

我首先得到了代表的参考.然后我记录回来的类名.在我的例子中,输出正确地说"app delegate的类名是CalculatorAppDelegate".

但是,下一行的断言失败了,我不明白为什么.

- (void)testAppDelegate 
{
    id appDelegate = [[UIApplication sharedApplication] delegate];
    NSLog(@"app delegate's class name is %@", NSStringFromClass([appDelegate class]));
    NSLog(@"is it kind? %i", [appDelegate isKindOfClass:[CalculatorAppDelegate class]]);
    NSLog(@"is it member? %i", [appDelegate isMemberOfClass:[CalculatorAppDelegate class]]);
    NSLog(@"class == class %i", [appDelegate class] == [CalculatorAppDelegate class]);
    STAssertTrue([appDelegate isKindOfClass:[CalculatorAppDelegate class]], @"wtf");
}

什么情况可能导致NSStringFromClass()返回正确的类名,而isKindOfClass返回false？

2011-03-19 15:51:13.864 Calculator[40092:207] app delegate's class name is CalculatorAppDelegate
2011-03-19 15:51:13.864 Calculator[40092:207] is it kind? 0
2011-03-19 15:51:13.865 Calculator[40092:207] is it member? 0
2011-03-19 15:51:13.865 Calculator[40092:207] class == class …