iOS 6 UITextField Secure - 如何检测退格清除所有字符？

问题描述

在iOS 6中，如果您将文字输入到安全文字栏位中，请变更为其他文字栏位，然后返回安全文字栏位并退回，所有字元都会被移除。我很高兴与这种情况发生，但是，我试图启用/禁用基于此安全文本字段中是否有字符的按钮。我知道如何确定字段中的字符，如果退格命中，但我无法确定如何清除所有的字符发生。

In iOS 6 if you type text into a secure text field, change to another text field, then come back to the secure text field and hit backspace, all of the characters are removed. I am fine with this happening, however, I am trying to enable/disable a button based on if this secure text field has characters in it or not. I know how to determine what characters are in the fields and if a backspace is hit but I am having trouble determining how to detect if clearing of all the characters is happening.

这是我使用的委托方法来获取字段的新文本，但是，我似乎不知道如何获取新文本（假设新文本将只是一个空白字符串）如果退格是

This is the delegate method I'm using to get the new text of a field, but, I can't seem to figure out how to get the new text (assuming the new text would just be a blank string) if a backspace is hit that clears all the characters.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    //returns the "new text" of the field
    NSString * text = [textField.text stringByReplacingCharactersInRange:range withString:string];
}

任何帮助都非常感激。

谢谢！

推荐答案

我使用这个解决方案。

I use this solution. It does not need local variables and sets the cursor position correctly, after deleting the char.

这是这个解决方案的混搭：

It's a mashup of this solutions:

• Backspace functionality in iOS 6 & iOS 5 for UITextfield with 'secure' attribute
• how to move cursor in UITextField after setting its value

 - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
    {
        if (range.location > 0 && range.length == 1 && string.length == 0)
        {
            // Stores cursor position
            UITextPosition *beginning = textField.beginningOfDocument;
            UITextPosition *start = [textField positionFromPosition:beginning offset:range.location];
            NSInteger cursorOffset = [textField offsetFromPosition:beginning toPosition:start] + string.length;

            // Save the current text, in case iOS deletes the whole text
            NSString *text = textField.text;


            // Trigger deletion
            [textField deleteBackward];


            // iOS deleted the entire string
            if (textField.text.length != text.length - 1)
            {
                textField.text = [text stringByReplacingCharactersInRange:range withString:string];

                // Update cursor position
                UITextPosition *newCursorPosition = [textField positionFromPosition:textField.beginningOfDocument offset:cursorOffset];
                UITextRange *newSelectedRange = [textField textRangeFromPosition:newCursorPosition toPosition:newCursorPosition];
                [textField setSelectedTextRange:newSelectedRange];
            }

            return NO;
        }

        return YES;
    }

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