Snapshotting a view that has not been rendered results in an empty snapshot.

错误提示 ： Snapshotting a view that has not been rendered results in an empty snapshot. Ensure your view has been rendered at least once before snapshotting or snapshot after screen updates

说明：我百度了一下，报这种错误的原因大多数都是 因为调用 相机的问题。我这个问题并不是因为相机，而是因为键盘问题。

代码如下：

-(void)viewWillDisappear:(BOOL)animated{    [super viewWillDisappear:animated];        //收回键盘    [self resignKeyBoard];}//收回键盘- (void)resignKeyBoard{    if (keyboardShown){        [[IQKeyboardManager sharedManager] resignFirstResponder];        [self.view endEditing:YES];        return;    }else{        return;    }}

暂时我认为的问题是我在基类的-(void)viewWillDisappear:(BOOL)animated 频繁的调用收回键盘方法，改过以后暂时没有报过错误了。（简单的记录一下，具体原因暂不清楚，应该是[[IQKeyboardManager sharedManager] resignFirstResponder]这句的问题吧）。