In my application I used two tableViews. For the first table all delegate and datasource methods are called. When I add the second table and call the method
[self.tableView reloadData];
cellForRowAtIndex method is not called. In the second table, the number of sections is 1 and the number of rows is 5. I set the delegate and datasource for tableView programatically.
It can be due to any of the below resons :
You have not connected the outlet to second table you are reloading.
You have not assign delegate as yourtable.delegate= self;
So if there is any of the missing case fix it.
When NSAssert(self.tableView.dataSource, #"No datasource"); is crashing, you haven't set the dataSource of the tableView correctly.
The NSAssert will crash your app if the condition inside the parenthesis of the assert validates to false (or 0, or in this case nil).
Wherever you create your tableView, make sure that you set the dataSource (and probably delegate too) correctly.
Regarding setting the dataSource correctly, don't make the mistake to set the dataSource to a newly created instance of your viewController. Most likely you want to use self.tableView.dataSource = self;.
Related
I met a question that i ensured setted datasource and delegate ，implemention two datasource methods ，but compiler not runnin this two methods，have someone tell me why?
When you assign self to tableView's dataSource, you have to make sure your tableView is not nil, then everything will be ok.
tableView:numberOfRowsInSection is sent to the delegate of a UITableView to find out how many rows it needs to have in a given section.
My question is, when and how often is this method called?
The method is called very first time the tableview is getting loaded and if you are more interested in the delegates then put a breakpoint and check when and where which delegate is called and how many times.
Below are the instances when that function will get called,
For the first time when table is loaded
the time you reload the table data
the time you add/update/delete your row or sections dynamically.
The method - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section is a protocol method of the UITableViewDataSource - protocol. It will be called
the very first time your table view is loaded based on that you have set the dataSource properly, e.g.
self.yourTableView.dataSource = self;
If you are interested in updating your table again at a later time you can call
[self.yourTableView reloadData];
in order to reload the entire table. If you are only interested in reloading a part of your table you can do something similar to
NSIndexSet *reloadSet = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, [self numberOfSectionsInTableView:self.yourTableView])];
[self.yourTableView reloadSections:reloadSet withRowAnimation:UITableViewRowAnimationAutomatic];
Hope it helps!
My question is, when and how often is this method called?
Short Answer : When your UITableView needs to update something.
Long Answer : Delegates Methods generally called themselves however it may be called multiple times when your UITableView needs to update something. By default, it's called very first time the tableview is getting loaded or updated (reloaded).
It depends on how often user will scroll UITable view to section and how many sections there are. This value, which is returned by this function and is casched. Method will need be revoked if you will update content of table view (filtering results, or updating data via reloadData).
Best thing for you will be to add logging to this function and check this yourself.
Here is a short summary of the situation:
I have a TableViewController with a number of cells.
In one of the cells I have a UITextField. This cell is of a custom UITableViewCell class. This class implements the UITextFieldDelegate protocol and the method textFieldDidEndEditing:
Within the method textFieldDidEndEditing: I store the value of the TextField into CoreData.
This all works great.
My question relates to reloading the TableView:
After certain actions of the user I reload the data of the UITableView by calling [self.tableView reloadData]
If, when I call this method, the above mentioned TextField is first responder, the textFieldDidEndEditing: method will be called, causing my CoreData related code to execute.
When the TableView is being reloaded I do not want the custom TabelViewCell to do anything at all.
Is there a way, the TableViewCell can be aware of the TableView being reloaded? So I can check for this within the textFieldDidEndEditing: method?
In the meantime I have solved it in the following way:
When this TableViewCell is being created I let the ViewController store a reference to it.
Before calling [self.tableView reloadData] I first inform the Cell by setting a custom property _cell.tableWillReload = YES
I will check for this property within the textFieldDidEndEditing: method.
I was thinking maybe there is a different, more default way, for TableViewCells to know they surroundingTableView is reloading?
Try This :-
[yourTextFieldOfCell resignFirstResponder];
before calling [self.tableView reloadData];
I've been stuck on this for all day.
I have a Nib file with a custom table cell wich I use to load into a
tableView instance variable of a view controller.
In the view controller I have a Search Bar and a Table View IBOutlets and a NSMutableArray to store my data as instance variables, among other stuff.
I have an object wich does asynchronous calls to an external API using Restkit so I define my view controller as it's delegate to receive the data when the request is finishe, save it on the NSMutableArray and then trigger a reloadData.
Because I'm making asynchronous calls the method shouldReloadTableForSearchString is in charge of sending the request and then return NO.
If I return YES instead of NO, making a call to reloadData after, my cells get loaded into the tableView one step back of my calls, that means that if I type the first letter nothing happens but on the second letter I get the results from the first letter. That behavior it's ok because the instance variable are setted after shouldReloadTableForSearchString returning YES. That is expected, Ok.
The problem that I'm facing is that if I use only reloadData, with shouldReloadTableForSearchString returning NO, the cells are not being assigned to the tableView. I checkhed and cellForRowAtIndexPath is being called and every cell is created with the data but it does not show.
Maybe I have problems with the datasource property, but I'm not sure.
I don't get the difference. Any Ideas?
I've got a UITableView set up and working, and now I have a little issue. I need to reload the tableView's data whenever the view loads, and one thing which I can't get working is attempting to reload the data, when there was no data in the table view to begin with.
Basically the list is of variable length, and the contents are loaded from a file, what I want to know is, is there I way I can force the table to reload and not have it ignore the datasource methods, as is what happens whenever [tableView reloadData] is called.
[tableView reloadData] relies entirely on the data source methods! So, the only way you would see your data source methods beind ignored would be that you have not set the data source (and perhaps delegate) of your table view to be the object you want to be the data source. You can set these through Interface Builder, or programatically, e.g.:
tableView.dataSource = self;
tableView.delegate = self;
whenever the view loads
Where do you call reloadData? Do you call it in -viewDidLoad method? If yes it is probably incorrect, because -viewDidLoad is called only once - when view of the corresponding UIViewController is created (on the first usage). Maybe you should take a look at -viewWillAppear which is called(assuming correct usage of UIViewController) whenever view is going to be displayed.
The other possible reason is that if you do use -viewWillAppear (or -viewDidAppear) it is not triggered at all. This can happen if you use a custom UIViewController hierarchy. In that case you must call it with your own hands (there are exceptions - UINavigationController for example does this for you, but simple [someView addSubview:myController.view] doesn't).
Also please check if delegates are set correctly and tableView is not equal to nil (as you know messages to nil are just ignored).
datasource methods aren't ignored when u call [tableView reloadData];
Did u set the IBOUTLET and the sources right?