Compare the text of two text fields

问题

How do you compare the text in two text fields to see if they are the same, such as in "Password" and "Confirm Password" text fields?

if (passwordField == passwordConfirmField) {

    //they are equal to each other

} else {

    //they are not equal to each other

}

回答1:

In Objective-C you should use isEqualToString:, like so:

if ([passwordField.text isEqualToString:passwordConfirmField.text]) {
    //they are equal to each other
} else {
    //they are *not* equal to each other
}

NSString is a pointer type. When you use == you are actually comparing two memory addresses, not two values. The text properties of your fields are 2 different objects, with different addresses.
So == will always¹ return false.

---

In Swift things are a bit different. The Swift String type conforms to the Equatable protocol. Meaning it provides you with equality by implementing the operator ==. Making the following code safe to use:

let string1: String = "text"
let string2: String = "text"

if string1 == string2 {
    print("equal")
}

And what if string2 was declared as an NSString?

let string2: NSString = "text"

The use of == remains safe, thanks to some bridging done between String and NSString in Swift.

---

1: Funnily, if two NSString object have the same value, the compiler may do some optimization under the hood and re-use the same object. So it is possible that == could return true in some cases. Obviously this not something you want to rely upon.

回答2:

You can do this by using the isEqualToString: method of NSString like so:

NSString *password = passwordField.text;
NSString *confirmPassword = passwordConfirmField.text;

if([password isEqualToString: confirmPassword]) {
    // password correctly repeated
} else {
    // nope, passwords don't match
}

Hope this helps!

来源：https://stackoverflow.com/questions/6905751/compare-the-text-of-two-text-fields