iOS--textfield的拓展

textField.attributedPlaceholder = [[NSAttributedString alloc] initWithString:placeholder attributes:@{NSForegroundColorAttributeName: [UIColor blueColor],NSFontAttributeName:[UIFont systemFontOfSize:20]}];

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
NSMutableString* str = [NSMutableString stringWithString:textField.text];

//判断是输入内容，还是del键删除内容。
if ([string length] > 0) {
[str insertString:string atIndex:range.location];
}
else{
[str replaceCharactersInRange:range withString:@""];
}

if ([textField isEqual:_verifyCodeField]) {
if ([str length] > verifyCodeLength) {
return NO;
}
}

return YES;
}