UITextInput protocol usage for UITextField and UITextView to manage selection results in crash

问题

UITextField and UITextView both adopt the UITextInput protocol. UITextView's selectedRange property returns NSRange, where UITextField doesn't have any selection properties/methods. I'd like to use one routine to manage insertion in either UITextField or UITextView.

So I do the following:

    id<UITextInput> textInput = nil;

    if ([self.aTextView isFirstResponder]) {
        textInput = self.aTextView;
    } else if ([self.aTextField isFirstResponder]) {
        textInput = self.aTextField;
    }

    if (textInput != nil) {
        UITextRange * selectedRange = textInput.selectedTextRange;
        // ...
    }

Only to promptly crash with 'unrecognized selector sent to instance' on the selectedTextRange property.

What am I doing wrong?

[EDIT: seems to work in iOS 5, but crashes on device in iOS 4. Is this a change in iOS 5? The docs say the protocol is 3.2+.]

回答1:

I verified in my own app that UITextView and UITextField both crash with -[UITextView selectedTextRange]: unrecognized selector in the iOS 4 simulator but not the iOS 5 simulator.

The answer to this question suggests that the conformance to UITextInput is a new thing in iOS 5: Can I select a specific block of text in a UITextField? . So it appears that the protocol itself is iOS 3.2, but UITextView/Field didn't make use of that protocol before iOS 5.

回答2:

@Absinthe's edit is correct. UITextField didn't start following the UITextInput protocol until iOS 5.

来源：https://stackoverflow.com/questions/7923659/uitextinput-protocol-usage-for-uitextfield-and-uitextview-to-manage-selection-re