如何验证字符串是否为空值？

Question

抱歉，但我仍在努力使该代码正常工作。如果使用 2 位数字，它可以工作，但如果使用一位数字，它就会崩溃。如何验证 NSString *secDigit 是否有值或为空。我希望我的问题很清楚。提前致谢。

NSString *depositOverTotalRwy = [NSString stringWithFormat:@"%@", [deposit text]];
NSArray *components = [depositOverTotalRwy
                       componentsSeparatedByString:@"/"];
NSString *firstThird = [components objectAtIndex:0];

    char firstChar = [firstThird characterAtIndex:0];
    char secChar = [firstThird characterAtIndex:1];
    NSString *firstDigit = [NSString stringWithFormat:@"%c",firstChar];
NSString *secDigit = [NSString stringWithFormat:@"%c", secChar];

    NSLog(@" i'm %@", firstDigit);
    NSLog(@" i'm %@", secDigit);

if ([firstDigit  isEqualToString: @"1"]) {
    firstDigit=@"wet";
    NSLog(@"wet");
}
if ([firstDigit  isEqualToString: @"2"]) {
    firstDigit=@"wet";
    NSLog(@"snow");

}
if ([firstDigit  isEqualToString: @"3"]) {
    firstDigit=@"wet";
    NSLog(@"ice");
    }

if ([secDigit  isEqualToString: @"1"]) {
    secDigit=@"wet";
    NSLog(@"wet");
}
if ([secDigit  isEqualToString: @"2"]) {
    secDigit=@"snow";

    NSLog(@"snow");
}
if ([secDigit  isEqualToString: @"3"]) {
    secDigit=@"ice";
    NSLog(@"ice");
}

感谢你们所有人......这是我的代码（现在正在工作）：

   NSString *depositOverTotalRwy = [NSString stringWithFormat:@"%@", [deposit text]];
NSArray *components = [depositOverTotalRwy
                       componentsSeparatedByString:@"/"];
NSString *firstThird = [components objectAtIndex:0];

    char firstChar = [firstThird characterAtIndex:0];
    NSString *firstDigit = [NSString stringWithFormat:@"%c",firstChar];

    NSLog(@" i'm %@", firstDigit);

if ([firstDigit  isEqualToString: @"1"]) {
    firstDigit=@"wet";
    NSLog(@"wet");
}
if ([firstDigit  isEqualToString: @"2"]) {
    firstDigit=@"wet";
    NSLog(@"snow");

}
if ([firstDigit  isEqualToString: @"3"]) {
    firstDigit=@"wet";
    NSLog(@"ice");
    }
if ([firstThird length] >1) {
    char secChar = [firstThird characterAtIndex:1];
    NSString *secDigit = [NSString stringWithFormat:@"%c", secChar];


if ([secDigit  isEqualToString: @"1"]) {
    secDigit=@"wet";
    NSLog(@"wet");
}
if ([secDigit  isEqualToString: @"2"]) {
    secDigit=@"snow";

    NSLog(@"snow");
}
if ([secDigit  isEqualToString: @"3"]) {
    secDigit=@"ice";
    NSLog(@"ice");
}
}

Answer 1

我猜您的代码在这一行中崩溃了：

char secChar = [firstThird characterAtIndex:1];

这是因为您尝试访问字符串边界之外的字符。您需要首先检查字符串的长度来防止这种情况：

if ([firstThird count] > 1) {
    // String has 2 or more characters, do all the stuff that involves
    // a second character.
    char secChar = [firstThird characterAtIndex:1];
    NSString *secDigit = [NSString stringWithFormat:@"%c", secChar];

    if ([secDigit  isEqualToString: @"1"]) {
        secDigit=@"wet";
        NSLog(@"wet");
    }
}

但我也建议不要在这里使用 NSString，因为您已经有一个 char。只需做这样的事情：

if ([firstThird count] > 1) {
    // String has 2 or more characters, do all the stuff that involves
    // a second character.
    char secChar = [firstThird characterAtIndex:1];

    if (secChar == '1') {
        secDigit=@"wet";
        NSLog(@"wet");
    }
}

Answer 2

我认为这就是您正在寻找的：

char secChar;
if(firstThird.length > 1)
{
    secChar = [firstThird characterAtIndex:1];
}

Answer 3

根据此

http:// /developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html

NSString“如果索引超出接收器末尾，则引发 NSRangeException”

因此，您的代码：

char secChar = [firstThird characterAtIndex:1];

是问题所在（您应该在调试器控制台中看到）

首先检查长度

  if ([firstThird length] < 2) {
       // handle the case where it is one digit
  }

Answer 4

您可以使用 NSString length 检查字符串中的字符数。并修改你的代码
因为

NSString *depositOverTotalRwy = [NSString stringWithFormat:@"%@", @"23"];
NSArray *components = [depositOverTotalRwy
                       componentsSeparatedByString:@"/"];
NSString *firstThird = [components objectAtIndex:0];


unichar firstChar;
unichar secChar;

if([firstThird length]>1){
    firstChar = [firstThird characterAtIndex:0];
    secChar = [firstThird characterAtIndex:1];
} else {
    firstChar = [firstThird characterAtIndex:0];
    secChar = 0;
}

switch (firstChar) {
    case '1': /* Do your stuff*/break;
    case '2': /* Do your stuff*/break;
    case '3': /* Do your stuff*/break;           
    default:
        break;
}

switch (secChar) {
    case '1': /* Do your stuff*/break;
    case '2': /* Do your stuff*/break;
    case '3': /* Do your stuff*/break;           
    default:
        break;
}

您可以使用 unichar 而不是 char。并且可以在 switch 语句中执行检查。
如果您使用 char，则会从 unichar 到 char 进行转换，对于某些字符，您可能会丢失实际值。所以使用 unichar 是安全的...

如果你想将 unichar 转换为字符串，只需编写代码
NSString * stringChar = [NSString StringWithFormat:@"%C",unicharVariable];

就是这样...