在iOS中，为什么viewWithTag方法返回nil？

Question

Today, I met a very strange thing.

I have a tableview which is built by Storyboard.
the type of the tableview is Static and Grouped
In one of its Cell , I have a cell with a switch(which is set ON in Storyboard).
I set the switch's tag to 10000816 by Storyboard.

I try to use [self.tableview viewWithTag 10000816] to get the switch in the tableview's controller. Failed.

OK. I then try to get the Cell first and try [cell viewWithTag] and somehow, it succeed.

Then I wonder why.
So I just left the following line uncommented.

UITableViewCell* cell =  [self.tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]];

Following by

UISwitch* switchButton = [self.tableView viewWithTag: 10000816];
    [switchButton setOn:NO animated:YES];

OK , this time , succeed again.
And I comment the Get-Cell line,which I think irrelevant.
then strange thing happened.It failed. The only change I had made is just a irrelevant line. So strange.

Question

Why will viewWithTag return nil if I just comment the Get-Cell line?

- (void) switchOff{ 
  //****** the line below is the magic Get-Cell  line , if I comment this line , viewWithTag will return nil    
     UITableViewCell* cell =  [self.tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]];


    UISwitch* switchButton = [self.tableView viewWithTag: 10000816];    
    [switchButton setOn:NO animated:YES];  
}

[update]
my switchOff is called in - (void)viewDidAppear:

- (void)viewDidAppear:(BOOL)animated{
    [self switchOff]
}

Answer 1

If your tableview is a Prototype one (one whose value will be filled by cellForRowAtIndexPath method) then dropping a cell inside the tableview, you wont get to see the cell, as that cell is not being created, so is its content.

If your tableview is a static one, only then will the storyboard content of a cell will be shown and you will get the control inside the cell with that tag.

I think your tableview is a prototype one, and as because the cell isnt being created so your [self.tableview viewWithTag 10000816] is returning nil as that control has not been created.

Hope could make you understand