如何限制NSTextField文本长度并保持它总是大写？ [英] How to limit NSTextField text length and keep it always upper case?

问题描述

需要一个NSTextField，文本限制最多为4个字符，并且始终以大写形式显示，但无法找出实现这一点的好方法。我试图通过一个验证方法的绑定，但验证只有当控制失去第一响应者，这是不好的时候被调用。

Need to have an NSTextField with a text limit of 4 characters maximum and show always in upper case but can't figure out a good way of achieving that. I've tried to do it through a binding with a validation method but the validation only gets called when the control loses first responder and that's no good.

Temporarly我做了工作通过观察通知NSControlTextDidChangeNotification在文本字段并让它调用方法：

Temporarly I made it work by observing the notification NSControlTextDidChangeNotification on the text field and having it call the method:

- (void)textDidChange:(NSNotification*)notification {
  NSTextField* textField = [notification object];
  NSString* value = [textField stringValue];
  if ([value length] > 4) {
    [textField setStringValue:[[value uppercaseString] substringWithRange:NSMakeRange(0, 4)]];
  } else {
    [textField setStringValue:[value uppercaseString]];
  }
}

但这肯定不是最好的做法它。任何更好的建议？

But this surely isn't the best way of doing it. Any better suggestion?

推荐答案

我做Graham Lee建议和它的工作正常，这里是自定义格式化程序代码：

I did as Graham Lee suggested and it works fine, here's the custom formatter code:

UPDATED：添加了Dave Gallagher报告的修复程序。谢谢！

UPDATED: Added fix reported by Dave Gallagher. Thanks!

@interface CustomTextFieldFormatter : NSFormatter {
  int maxLength;
}
- (void)setMaximumLength:(int)len;
- (int)maximumLength;

@end

@implementation CustomTextFieldFormatter

- (id)init {

   if(self = [super init]){

      maxLength = INT_MAX;
   }

  return self;
}

- (void)setMaximumLength:(int)len {
  maxLength = len;
}

- (int)maximumLength {
  return maxLength;
}

- (NSString *)stringForObjectValue:(id)object {
  return (NSString *)object;
}

- (BOOL)getObjectValue:(id *)object forString:(NSString *)string errorDescription:(NSString **)error {
  *object = string;
  return YES;
}

- (BOOL)isPartialStringValid:(NSString **)partialStringPtr
   proposedSelectedRange:(NSRangePointer)proposedSelRangePtr
          originalString:(NSString *)origString
   originalSelectedRange:(NSRange)origSelRange
        errorDescription:(NSString **)error {
    if ([*partialStringPtr length] > maxLength) {
        return NO;
    }

    if (![*partialStringPtr isEqual:[*partialStringPtr uppercaseString]]) {
      *partialStringPtr = [*partialStringPtr uppercaseString];
      return NO;
    }

    return YES;
}

- (NSAttributedString *)attributedStringForObjectValue:(id)anObject withDefaultAttributes:(NSDictionary *)attributes {
  return nil;
}

@end

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