关于给subView添加UIButton

在用户点击屏幕时，应该有一个带按钮的弹出窗出现。但是弹出窗出现，按钮没出现。不知道哪出错了。是在

subView中的subView。
-(void) popUpWithX:(int)x andY:(int)y {
    CGRect popUpRect = CGRectMake(x, y, 125, 75);
    popUp = [[UIView alloc] initWithFrame:popUpRect];
    popUp.backgroundColor = [UIColor whiteColor];
    popUp.layer.cornerRadius = 7.5f;
    popUp.layer.masksToBounds = YES;

    [self.view addSubview:popUp];
    UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 100, 30)];
    [button setTitle:@"Click me!" forState:UIControlStateNormal];
    [popUp addSubview:button];
}