I called [alert show],But nothing happened... why?

[shenguanjiejie]

FUIAlertView *alert = [[FUIAlertView alloc] initWithTitle:@"没有输入" message:@"密码不能为空" delegate:nil cancelButtonTitle:@"知道了" otherButtonTitles:nil, nil];
alert.titleLabel.textColor = [UIColor cloudsColor];
alert.titleLabel.font = [UIFont boldFlatFontOfSize:16];
alert.messageLabel.textColor = [UIColor cloudsColor];
alert.messageLabel.font = [UIFont flatFontOfSize:14];
alert.backgroundOverlay.backgroundColor = [[UIColor cloudsColor] colorWithAlphaComponent:0.8];
alert.alertContainer.backgroundColor = [UIColor midnightBlueColor];
[alert show];