objective-c - 无法缩短 NSString 长度

Question

我试图让这个程序只有在小数为 .5 时才有小数。我一直在尝试使用 [string substringToIndex:[string length] - 2] 但它什么也没做。是因为它不能追加 float 吗？

float inchesInField = [sizeField.text floatValue];
float shoeSize = inchesInField * 3 - 22;
NSMutableString *appendedShoeSize = [[NSMutableString alloc]
                                            initWithFormat:@"%.1f", shoeSize];

if ([appendedShoeSize hasSuffix:@".3"] || [appendedShoeSize hasSuffix:@".5"] ||
    [appendedShoeSize hasSuffix:@".4"] || [appendedShoeSize hasSuffix:@".6"])
{
    [appendedShoeSize substringToIndex:[appendedShoeSize length] - 2];
    [appendedShoeSize appendString:@" ½"];
} 

if ([appendedShoeSize hasSuffix:@".0"] || [appendedShoeSize hasSuffix:@".1"] ||
    [appendedShoeSize hasSuffix:@".2"])
{
    [appendedShoeSize substringToIndex:[appendedShoeSize length] - 2];
}

Answer 1

因为 NSString 的 substringToIndex: 方法返回的是新字符串，并没有修改原字符串。 appendString: 很好，但是 substringToIndex: 是 NSString 的一个方法，所以它不会编辑原始字符串。

应该这样做:

float inchesInField = [sizeField.text floatValue];
float shoeSize = inchesInField * 3 - 22;
NSMutableString *appendedShoeSize = [[NSMutableString alloc] initWithFormat:@"%.1f", shoeSize];

if ([appendedShoeSize hasSuffix:@".3"] || [appendedShoeSize hasSuffix:@".5"] || [appendedShoeSize hasSuffix:@".4"] || [appendedShoeSize hasSuffix:@".6"]) {

    appendedShoeSize = [[appendedShoeSize substringToIndex:[appendedShoeSize length] - 2] mutableCopy];
    [appendedShoeSize appendString:@" ½"];
} 

if ([appendedShoeSize hasSuffix:@".0"] || [appendedShoeSize hasSuffix:@".1"] || [appendedShoeSize hasSuffix:@".2"]) {

    appendedShoeSize = [[appendedShoeSize substringToIndex:[appendedShoeSize length] - 2] mutableCopy];
}