iOS UI基础

    //找到已经创建好的UITextField
    UITextField *textField = [[UITextField alloc] initWithFrame:CGRectMake(50, 100, RFSCREEN_W - 100 , 45)];
    textField.leftImageName = @"login_user_icon"
    //设置边框样式
    textField.borderStyle = UITextBorderStyleNone;
    //通过layer设置圆角
    //textField.layer.cornerRadius = 10;
    textField.layer.borderColor = Color_White.CGColor;
    textField.layer.borderWidth = 1;
    // 设置字体颜色
    textField.textColor = Color_White;
    // 输入框中是否有个叉号，在什么时候显示，用于一次性删除输入框中的内容
    textField.clearButtonMode = UITextFieldViewModeAlways;
    //第一响应者，一个界面可能有多个可输入的控件，哪一个正在编辑哪一个就是第一响应者
    [textField becomeFirstResponder];
    // 设置左边图标
    UIImageView *leftImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"login_user_icon"]];
    leftImageView.frame = CGRectMake(0, 0, 50, 50);
    leftImageView.contentMode = UIViewContentModeCenter;
    textField.leftView = leftImageView;
    //设置左视图的显示模式
    textField.leftViewMode = UITextFieldViewModeAlways;
    // 设置键盘的样式
    textField.keyboardType = UIKeyboardTypeNumberPad;
    // 设置占位文字
    textField.placeholder = @"请输入用户名";
    // 设置占位文字的颜色
    [textField setValue:Color_White forKeyPath:@"placeholderLabel.textColor"];
    
    [self.view addSubview:textField];

 限定只可以输入数字和6位长度

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    NSString *text = [textField text];
    NSCharacterSet *characterSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];
    string = [string stringByReplacingOccurrencesOfString:@" " withString:@""];
    if ([string rangeOfCharacterFromSet:[characterSet invertedSet]].location != NSNotFound) {
        return NO;
    }
    text = [text stringByReplacingCharactersInRange:range withString:string];
    text = [text stringByReplacingOccurrencesOfString:@" " withString:@""];
    
    if ([text stringByReplacingOccurrencesOfString:@" " withString:@""].length >= 7) {
        return NO;
    }
    
    [textField setText:text];
    _confirmButton.enabled = text.length > 0 ? YES : NO;
    return NO;
}