iOS UITextField 显示银行卡格式的方法

类名 ()<uitextfielddelegate>
self.textfield.delegate = self;

- (bool)textfield:(uitextfield *)textfield shouldchangecharactersinrange:(nsrange)range replacementstring:(nsstring *)string
{
  if (textfield == self.contenttextfield) {
    // 4位分隔银行卡卡号
    nsstring *text = [textfield text];
    nscharacterset *characterset = [nscharacterset charactersetwithcharactersinstring:@"0123456789\b"];
    string = [string stringbyreplacingoccurrencesofstring:@" " withstring:@""];
    if ([string rangeofcharacterfromset:[characterset invertedset]].location != nsnotfound) {
      return no;
    }
    text = [text stringbyreplacingcharactersinrange:range withstring:string];
    text = [text stringbyreplacingoccurrencesofstring:@" " withstring:@""];
    nslog(@"%@",text);
//    text为输入框内的文本，没有“ ”的内容
    nsstring *newstring = @"";
    while (text.length > 0) {
      nsstring *substring = [text substringtoindex:min(text.length, 4)];
      newstring = [newstring stringbyappendingstring:substring];
      if (substring.length == 4) {
        newstring = [newstring stringbyappendingstring:@" "];
      }
      text = [text substringfromindex:min(text.length, 4)];
    }
    newstring = [newstring stringbytrimmingcharactersinset:[characterset invertedset]];
    if ([newstring stringbyreplacingoccurrencesofstring:@" " withstring:@""].length >= 21) {
      return no;
    }
    [textfield settext:newstring];
    return no;
  }
  return yes;
}