检查Objective-C中的相等性

当你使用 == These objects are different 因为虽然字符串相同,但它们存储在内存中的不同位置:

NSString* foo = @"Foo";
NSString* bar = [NSString stringWithFormat:@"%@",foo];
if(foo == bar)
    NSLog(@"These objects are the same");
else
    NSLog(@"These objects are different");

-isEqualToString: NSString . 此代码将返回 These strings are the same 因为它比较的是字符串对象的值而不是它们的指针值:

NSString* foo = @"Foo";
NSString* bar = [NSString stringWithFormat:@"%@",foo];
if([foo isEqualToString:bar])
    NSLog(@"These strings are the same");
else
    NSLog(@"These string are different");

isEqual: 方法 NSObject . -isEqual: 当您知道两个对象都是 NSString字符串

- (void)CheckKeyWithString:(NSString *)string
{
   //foreach key in NSMutableDictionary
   for(id key in dictobj)
     {
       //Check if key is equal to string
       if([key isEqual:string])
          {
           //do some operation
          }
     }
}