I am designing a one-to-one chatting interface using table view. This table view is modified to show bubbles as some new message arrives. The new message arrives through a push-notification in this case. I call following code in my function which receives message through the push notification:
-(void)messageReceived: (NSString *)message{
_message=[message retain];
[tableView reloadData];
}
However, it seems this does not reload my table view.
If I place the call for reloadData in the viewDidAppear function, it reloads fine. It also reloads fine, if I place the reloadData call in a function whose return type is IBAction (ex: a function binding to button click)
What could be the reason for reloadData to not get triggered through custom declared functions ?
reloaddata method is called but the trick here that you didn't add the incoming message to the datasource that the tableview load from !
may be you have not Connect the Tableview with table view Delegates and Datasource
Objective-C
#interface YourClass : UIViewController <UITextFieldDelegate, UITextViewDelegate>
yourtableview.delegate = self;
yourtableview.dataSource = self;
[tableView reloadData];
Swift 3
class YourClass: UIViewController , UITableViewDelegate, UITableViewDataSource
yourtableview.delegate = self
yourtableview.dataSource = self
yourtableview.reloadData()
the other way is! for Swift and Objective-C both.
Right Click on the Table view and drag and drop the delegates.
Related
I have a UITableView comprised of custom UITableViewCells. In each cell, there is a UILabel and a UISlider. Does anyone know how to, upon a change in value of one of the sliders, send the new value of the slider from the custom UITableViewCell (in a separate file) to the UITableViewController, so that I can then update the array from which the table was populated?
The closest I've got so far is a failed hack: firing a setSelected event when a slider value is changed. Whilst this highlights the changed custom cell, the event is not picked up by didSelectRowAtIndexPath in the UITableViewController.
Whilst code is always appreciated, a conceptual/method solution is what I am looking for.
Thank you in advance,
Jamie
What you need is called Delegate Pattern.
Quoting from there to explain what does it mean:
Delegation is a simple and powerful pattern in which one object in a
program acts on behalf of, or in coordination with, another object.
The delegating object keeps a reference to the other object—the
delegate—and at the appropriate time sends a message to it. The
message informs the delegate of an event that the delegating object is
about to handle or has just handled. The delegate may respond to the
message by updating the appearance or state of itself or other objects
in the application, and in some cases it can return a value that
affects how an impending event is handled. The main value of
delegation is that it allows you to easily customize the behavior of
several objects in one central object.
These diagrams will help you understand what goes on:
Architecture:
Operation:
Now as to how to implement it, this is what you have to do.
For Objective-C:
First of all, create delegate methods of your UITableViewCell. Lets name it ContactTableViewCell.
In your ContactTableViewCell.h file, do this:
#protocol ContactCellDelegate <NSObject>
#required
-(void) didMoveSliderWithValue:(float) value;
#end
#interface ContactTableViewCell : UITableViewCell
#property (weak, nonatomic) id<ContactCellDelegate> delegate;
Now conform your TableViewController to this delegate. Let's name your VC MyTableViewController.
In MyTableViewController.h, Do this:
#interface MyTableViewController : UIViewController <ContactCellDelegate> //Use UITableViewController if you are using that instead of UIViewController.
In your cellForRowAtIndexPath, before returning cell, add this line:
cell.delegate = self;
Add implementation for the delegate method INSIDE your MyTableViewController.m.
-(void) didMoveSliderWithValue: (float) value
{
NSLog(#"Value is : %f",value);
//Do whatever you need to do with the value after receiving it in your VC
}
Now let's get back to your ContactTableViewCell.m. In that file you must have added some IBAction to capture the value change event in slider. Let's say it is the following:
- (IBAction)sliderValueChanged:(UISlider *)sender {
self.myTextLabel.text = [#((int)sender.value) stringValue]; //Do whatever you need to do in cell.
//Now call delegate method which will send value to your view controller:
[delegate didMoveSliderWithValue:sender.value];
}
When you call delegate method, it will run the implementation that we wrote earlier in the MyTableViewController. Do whatever you need in that method.
What happens here is that your Cell sends the message to your desired VC (Which is delegate of the Cell), that "Hey, Call the delegate method that we wrote earlier in your body. I am sending you parameters right away". Your VC takes the parameters and does whatever you wanted it to do with that info and at that time.
For Swift:
First of all, your TableViewCell.swift file, create a protocol like this:
#class_protocol protocol ContactCellDelegate {
func didMoveSliderWithValue(value: Float)
}
Now in your Cell class, create a delegate property like:
var cellDelegate: ContactCellDelegate?
In your Slider IBAction, call the delegate method like this:
self.cellDelegate?.didMoveSliderWithValue(slider.value)
In your VC do these changes:
Make it conform to the delegate:
class MyTableViewController: UIViewController, ContactCellDelegate
Add this line before returning cell in cellForRowAtIndexPath
cell.cellDelegate = self //Dont forget to make it conform to the delegate method
Add the implementation of required delegate method:
func didMoveSliderWithValue(value:float) {
//do what you want
}
I have kept the Swift part precise and summarized because It should be very easy to change the detailed Obj-C explanation to Swift implementation. However If you are confused about any of the pointers above, leave a comment.
Also see: StackOverflow answer on using Delegate pattern to pass data back
I have a UICollectionView that's connected to myclass datasource and delegate. When I call [self.collectionview reloaddata] it works normally but after a while (random time and number of times) when I reload the collection again it doesn't work any more.
collection reference delegate and datasource are correctly defined.
self.devicesCollectionViewDataSource= devices;
self.devicesCollectionView.delegate = self;
self.devicesCollectionView.dataSource = self;
[self.devicesCollectionView reloadData];
Overwrite the setDelegate method of your collection view subclass, set a breakpoint and observe who's changing it.
-(void)setDelegate:(id<YOUR_PROTOCOL>)delegate {
_delegate = delegate; // breakpoint here -> look at the trace log, it should give you the caller that's overwriting your delegate
}
Clarification: this doesn't solve your problem per se, but at least you know where to look
Screencast: https://www.youtube.com/watch?v=ZwehDwITEyI
This is really bizarre. The problem is to do with a label outlet sitting in a custom-designed table cell. That cell is of my CustomCell class. (actually called RA_FormCell if you watch the screencast).
CustomCell.h
#property (weak, nonatomic) IBOutlet UILabel *dayOutlet;
-(void)controller:(id<CustomCellDelegate>)controller didUpdateDay:(NSString *)theDay;
CustomCell.m
// Method is called by a view controller
// (which is itself a delegate of the CustomCell class,
// hence the identifier you see below)
-(void)controller:(id<CustomCellDelegate>)controller didUpdateDay:(NSString *)theDay;
{
NSLog(#"Method called") // confirms to me that method is called
self.dayOutlet.text = #"Goodmorning";
NSLog(#"%#", self.dayOutlet.text); // displays (null)
}
That final log does actually appear, so the method is definitely being called. I have discounted the following:
self.dayOutlet.text is not written to elsewhere by any other method in the project
dayOutlet is connected to the label in the storyboard (and the label is not connected to anything else)
The label is not hidden underneath some accidental static label on the storyboard
The cell attributes on the storyboard include its class as CustomCell
No warnings or alerts in Xcode (I have been careful to avoid any circular imports)
The problem was that the controller:didUpdateDay: message was not sent to the correct instance of the cell class.
This occurred because I had not correctly assigned this cell to be the delegate for the view controller. For anyone interested, in my screencast at 3:50, you can see that I have the following in cellForRowAtIndexPath:
RA_FormCell *cell = [tableView dequeueReusableCellWithIdentifier:self.formCellArray[indexPath.row] forIndexPath:indexPath];
self.delegate = cell
However, this means that self.delegate got continually overwritten as the table cells were generated. As a result, my controller:didUpdateDay message was sent to the bottom cell of the table, and not the top one as I required.
The solution was simple - there's no need to have this second delegate at all. Instead, when the cell delegates to the view controller, it should pass self into the message it delegates:
id<CustomCellDelegate> strongDelegate = self.delegate;
if ([strongDelegate respondsToSelector:#selector(customCell:didChangeDay1:)])
[strongDelegate customCell:self didChangeDay1:[sender value]];
Then, in the implementation of this method by the delegate, simply end it by changing the outlet directly:
-(void)customCell:(RA_FormCell *)customCell didChangeDay1:(double)value
// put logic here
customCell.dayOutlet.text = #"No problem!";
In general, there should rarely be a need for a two-way delegate structure. Keep it one way, from A to B, and just remember to have A pass self in any messages it sends to B. That way, B will know the object the message came from, and be able to communicate back to A.
Thanks to Paulw11
I'm really going crazy on this.
But let me explain to you my little project first:
I have an Custom UITableView TDStartTableView.
Also in there I have some methods implemented for rendering the table. No problem there.
Inside of one TableViewCell there is a button.
When that Button is clicked it triggers this method:
- (void)triggerPush {
[self.delegate pushNextView];
}
self.delegate is specified in the .h file of TDStartTableView like this:
#property (nonatomic, weak) id<TDStartTableViewDelegate> delegate;
Also, the reference is set in my UITableViewController:
self.tableView.delegate = self;
So essentially what I'm trying to do is: Create a custom UITableView with Buttons etc. and then listen on the events from a ViewController that is implementing that UITableView and the protocol
So because the protocol forces me to implement pushNextView this method is in my UIViewController:
- (void)pushNextView {
NSLog(#"This works");
}
To this point everything works just fine, no problem there!
But now comes the tricky part.
I create a segue from my UIViewController to a new ViewController. I connect them via a segue and name the segue appropriately. pushToSecondStep.
Now one would think, that when I change the implementation of pushNextView to this
- (void)pushNextView {
[self performSegueWithIdentifier:#"pushToSecondStep" sender:self];
}
it works. But what I get is:
'Receiver (<TDFirstStepTableViewController: 0x8dc97d0>) has no segue with identifier 'pushToSecondStep''
Please help, I'm going crazy :D
The problem was, that I overwrote a constructor of TDStartTableView.
The proper form is that you implement all constructors, so that Objective-C can instantiate them all by itself:
- (id) initWithCoder:(NSCoder *)aDecoder {
self = [super initWithCoder:aDecoder];
return self;
}
Also when you implement a custom UITableView Widget you shouldn't use UITableViewController but UIViewController.
Also you don't initialize your custom UITableView yourself, Storyboard already does that for you, so if you want to set special variables for it like numberOfRows then just declare a property and then set it via a setter-method outside and call [tableView reloadData].
Also, thanks https://stackoverflow.com/users/1095089/shubhank for helping me in the chat :)
My application is using JASidePanels libraries and I had set them using storyboard. The center view is a UITableView and the left panel is a view in which I call a method (by pressing a button)
- (IBAction)reloadAllFilters:(UIButton *)sender{
MasterViewController *masterController = [self.storyboard instantiateViewControllerWithIdentifier:#"centerViewController"];
NSMutableArray *arrayOfFilterIds = [[NSMutableArray alloc] init];
// another code
masterController.filterIdsToDisplay = arrayOfFilterIds;
[masterController.tableView reloadData];
[self.sidePanelController toggleLeftPanel:self];
}
The thing is, that when the app starts, the number of rows returned by number, but after I call this method, the number of rows is 30 but I cant see nothing.
I think that the problem is that I am instantiating a new masterController and therefor I cant get the actual table view to be displayed? Or am I wrong? Can you please help me?
Yes you are right. You create a new master controller every time you call the method
From UIStoryboard reference:
This method creates a new instance of the specified view controller each time you call it.
You need to get the existing one.
Please set the delegate and datasource to your tableview
like this ...
tableView.delegate = masterController;
tableView.dataSource = masterController;