一、 UIColor 获取 RGB 值

UIColor *color = [UIColor colorWithRed:0.0 green:0.0 blue:1.0 alpha:1.0];
const CGFloat *components = CGColorGetComponents(color.CGColor);
NSLog(@"Red: %f", components[0]);
NSLog(@"Green: %f", components[1]);
NSLog(@"Blue: %f", components[2]);
NSLog(@"Alpha: %f", components[3]);

二、 修改textField的placeholder的字体颜色、大小

self.textField.placeholder = @"username is in here!";
[self.textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];
[self.textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];

推荐 使用attributedString进行设置.

NSString *string = @"";

    NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithString:string];
    
    [attributedString addAttribute:NSForegroundColorAttributeName
                             value:[UIColor redColor]
                             range:NSMakeRange(0, [string length])];
    
    [attributedString addAttribute:NSFontAttributeName
                             value:[UIFont systemFontOfSize:16]
                             range:NSMakeRange(0, [string length])];
    
    self.textField.attributedPlaceholder = attributedString;

三、判断NSString为纯数字
//判断是否为整形：

- (BOOL)isPureInt:(NSString*)string{
    NSScanner* scan = [NSScanner scannerWithString:string];
    int val;
    return[scan scanInt:&val] && [scan isAtEnd];
}

//判断是否为浮点形：

- (BOOL)isPureFloat:(NSString*)string{
    NSScanner* scan = [NSScanner scannerWithString:string];
    float val;
    return[scan scanFloat:&val] && [scan isAtEnd];
}

if( ![self isPureInt:insertValue.text] || ![self isPureFloat:insertValue.text])
{
    resultLabel.textColor = [UIColor redColor];
    
    resultLabel.text = @"警告:含非法字符，请输入纯数字！";
    
    return;
}