==和isEqualToString给出了奇怪的行为

Question

我有以下代码

NSString *firstName = @"1.6.1";
NSString *secondName = @"1.6.1";

if (!(firstName==secondName)) {
    NSLog(@"lock the app");
} else {
    NSLog(@"do not lock the app");
}

if (!([firstName isEqualToString:secondName])) {
    NSLog(@"lock the app");
} else {
    NSLog(@"do not lock the app");
}

我得到的输出是

do not lock the app
do not lock the app

但是当我使用firstName＆amp;的实际值时secondName，我的输出为

lock the app
do not lock the app

以下是firstName＆amp; secondName

 // this is coming from server
 firstName = [[NSUserDefaults standardUserDefaults] stringForKey:@"iPhoneAppVersion"];

 // this is coming from app version from iPhone
 secondName = [self appNameAndVersionNumberDisplayString];

- (NSString *)appNameAndVersionNumberDisplayString {
    NSDictionary *infoDictionary = [[NSBundle mainBundle] infoDictionary];
    NSString *appDisplayName = [infoDictionary objectForKey:@"CFBundleDisplayName"];
    NSString *majorVersion = [infoDictionary objectForKey:@"CFBundleShortVersionString"];
    NSString *minorVersion = [infoDictionary objectForKey:@"CFBundleVersion"];

    return [NSString stringWithFormat:@"%@",
            minorVersion];
}

如果我打印firstName＆amp; secondName，我的值分别为1.6.1，1.6.1。

在使用equals时，知道为什么有两个不同的输出？

Answer 1

==和isEqualToString:会有不同的行为。因为==运算符仅比较对象的地址，而isEqualToString:将比较字符串值。

您不应使用==进行字符串比较。