What are the most common reasons for an outlet (a class property) not being set during a bundle load?
I'm sorry; most likely I'm not using the correct terms. It's my first steps with iPhone OS development and Objective-C, so please bear with me. Here is more details. Basically, I'm trying to create a table view based form with a fixed number of static rows. I followed this example:
http://developer.apple.com/iphone/library/documentation/userexperience/conceptual/TableView_iPhone/TableViewCells/TableViewCells.html
Scroll down to The Technique for Static Row Content please. I have one nib file with one table view, three table cells and all connections set as in the example. The problem is that the corresponding cell properties in my controller are never initialised. I get an exception in cellForRowAtIndexPath complaining that the returned cell is nil: UITableView dataSource must return a cell from tableView:cellForRowAtIndexPath.
Here are the relevant parts from the implementation of the controller:
#synthesize cellA;
#synthesize cellB;
#synthesize cellC;
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView
numberOfRowsInSection:(NSInteger)section
{
return 3;
}
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
switch (indexPath.row)
{
case 0: return cellA; break;
case 1: return cellB; break;
case 2: return cellC; break;
default: return nil;
}
}
And here is the interface part:
#interface AssociatePhoneViewController : UITableViewController
{
UITableViewCell *cellA;
UITableViewCell *cellB;
UITableViewCell *cellB;
}
#property (nonatomic, retain) IBOutlet UITableViewCell *cellA;
#property (nonatomic, retain) IBOutlet UITableViewCell *cellB;
#property (nonatomic, retain) IBOutlet UITableViewCell *cellC;
#end
This must be possibly one of the the most embarrassing questions on StackOverflow. It looks like the most basic example code.
Is is possible that the cells are not instantiated with the nib file? I have them on the same level before the tabula view in the nib file. I tried to move them after the table view, but it did not make any difference.
Are table cells in some way special? Do I need to set some flag or some property on them in the nib file? I was under the impression that all classes (views, windows, controllers …) listed in a nib file are simply instantiated (and linked using the provided connections).
Could it possibly be some memory issue? The cell properties in my controller are not defined in any special way.
I found out what the problem was already some time ago, and I should have posted it earlier ... sorry. Here it goes.
The culprit was the Interface Builder - or perhaps me not using it correctly. I drag-dropped my view controller into a different nib file, and somehow managed to delete (or not fill) the NIB Name field. Either way, the view controller was instantiated without its NIB file.
try instantiating (alloc init) the cells in viewDidLoad
Related
I have a UITableView and it contains a custom UITableViewCell. To test, I have an array that has three strings in it. The UITableView delegate methods are called as expected, however, the tableView:cellForRowAtIndexPath delegate is always passed an NSIndexPath instance whose row property is always == nil:
tableView:cellForRowAtIndexPath is called 3 times (once for each object in my array). I added the tableView from within the designer (storyboard) and created an outlet for it. The UITableViewCell instances appear to be correctly instantiated which each call to this delegate. I just can't wrap my head around why the [indexPath row] value is always nil.
Interface(s):
In the implmentation file:
#interface FirstViewController ()
#property(nonatomic, strong)AppDelegate *sharedDelegate;
#property(nonatomic, strong)NSArray *userList;
#end
In the header:
#interface FirstViewController : UITableViewController <FacebookDelegate>
#property (strong, nonatomic) IBOutlet UITableView *tableView;
#end
Init the custom cell:
-(void)viewDidLoad
{
[self.tableView registerClass: [ListCategoryCell class]forCellReuseIdentifier:#"ListCategoryCell"];
self.userList = #[#"d", #"g", #"f"]; // make some test data
}
And the delegate this is driving me mad:
//NSIndexPath.row is nil ?!
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *MyIdentifier = #"ListCategoryCell";
ListCategoryCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier forIndexPath:indexPath];
if (cell == nil) {
cell = (ListCategoryCell *)[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:MyIdentifier];
}
cell.titleLabel.text = [self.userList objectAtIndex:[indexPath row]];
cell.detailLabel.text = #"Detail";
return cell;
}
Am I missing something? Thanks!
Working Now
I left out some context (and I should not have) that I believe was very relevant to my problem. I created a UIViewController originally and then added a UITableView to this as the view. In the UITableView I created a custom prototype cell. I did all the house work:
UIViewController implemented the UITableViewDelegate & UITableViewDatasource.
Created and outlet for the UITableView.
Hooked up all the outlets
Everything seemed to work except for the fact that indextPath.row property was always nil. Some resources I found suggested that custom cells were not visible before the uitableview delegates were called.
In the end I made my class a subclass of UITableViewController. Things started working. I am still curious why my original attempt was failing.
Thanks for everyone's time. Some great comments helped me investigate some topics that are "good to know".
You need to provide at least two methods in view controller if you want it to manage your table view. They are:
-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
-(UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
You've already provided the second, so your table view actually can produce cells but it doesn't know how many.The default value the first method returns is nil.That is the reason why you don't even have an index path.
Optionally:
-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
The default value is one,so you don't need to override this in case you have only one section
Make sure your view controller also follows delegate and datasource protocols.
I have read about using underscores to fix compiler warnings that say "Local declaration hides instance variable," but I have not been able to implement a fix. The solutions I have read about say to use an underscore in my .h file, and the #synthesize part of in my .m file. However, I do not synthesize my tableView. Please see my header file below:
.h File
#interface ListViewController : GAITrackedViewController <UISearchDisplayDelegate,
UISearchBarDelegate, UITableViewDataSource, UITableViewDelegate> {
IBOutlet UITableView *tableView;
}
.m File
//SYNTHESIZE
#synthesize listItems, filteredListItems, savedSearchTerm, savedScopeButtonIndex,
searchWasActive, mapView, loadingImageView, loadingActivity;
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
//FIRST WARNING for tableView HERE
if (tableView == self.searchDisplayController.searchResultsTableView){
return [self.filteredListItems count];
}
else{
return [self.listItems count];
}
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
//SECOND WARNING for tableView HERE
[tableView setRowHeight: 60.00];
return 1;
}
You have an outlet/property named tableView and your delegate method also contains tableView.
So you need to change either of them. Typically you go to change the argument names of delegate and datasource as
- (NSInteger)tableView:(UITableView *)aTableView
numberOfRowsInSection:(NSInteger)section {
Change :
IBOutlet UITableView *tableView;
To :
IBOutlet UITableView *tableView1;
Make the same required changes in your .m file also. This warning is coming because in below delegate method:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
There is a reference of UITableView with name tableView and you have given the same name. Scope of this variable is function level where as scope of your variable declare in .h is class level.
Dont use same name : IBOutlet UITableView *tableView; use tableview or table_View
I do also spent lot of time on this issue. Finally I could solve this problem.
The thing is we should take care of outlets which are created by us. If you change outlets names then you must connect them properly after change.In my case after lot of struggle I could finish this issue hope it will help others....
For example if You have an outlet/property named tableView and your delegate method also contains tableView.
So you need to change either of them. Typically you go to change the argument names of delegate and datasource as
Change :
IBOutlet UITableView *tableView;
To :
IBOutlet UITableView *tableView1;
For more information visit this link->Local Declaration Hides Instance Variable - tableView Not Synthesized
I am trying to write an app with a 'main page' of UIButtons that when tapped will Segue to UITableView, which will in turn Segue to another View etc. I have no errors or warnings in my code, and I thought I designed it well, but when I run the app the PrototypeCells don't even appear.
This is how I have my Storyboard set up right now (I'm sorry but I can't post images yet, as I'm a new user). The little beer mug is a UIButton that successfully performs the Segue to the UITableView window (this is the one that doesn't load the PrototypeCells).
The Brew View Controller has no code in it other than the defaulted methods.
I created a class called Brewery and gave it the following properties
#property (nonatomic, copy) NSString *name;
#property (nonatomic, copy) NSString *address;
#property (nonatomic, copy) NSString *info;
#property (nonatomic, copy) NSString *brews;
I created the Brewery View Controller and added the following methods along with the default code
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Return the number of rows in the section.
return [self.breweries count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"BreweryCell"];
Brewery *brewObject = [self.breweries objectAtIndex:indexPath.row]; //might be an error in here
cell.textLabel.text = brewObject.name;
return cell;
}
Yet when I run this, the PrototypeCells aren't even showing. The ReuseIdentifier matches both in storyboard and in the code, and the View is attached to the dataSource and the Delegate. Can anyone help me figure out what I'm doing wrong? I am also new to site, so please tell me if there is something I am doing wrong or if you need more information to assist me.
Even though you have said you have set the dataSource, if numberOfSectionsInTableView is not being called then it means the data source is not set correctly.
I suggest checking this in viewDidAppear and logging the data source and delegate, and programatically checking the equal self.
There are a few pitfalls with setting IBOutlets in interface builder.
From what you have said in your blurb:
the View is attached to the dataSource and the Delegate
This is wrong. It should be the file's owner which is the View Controller.
So I have a Custom UITableViewCell that holds a reference to its containing view controller (the VC that has its table in it).
// MyCell.h
#import <UIKit/UIKit.h>
#import "RootViewController.h"
#interface MyCell : UITableViewCell
#property (nonatomic, strong) IBOutlet RootViewController *rootViewController;
-(IBAction)checkBoxClicked:(UIButton*)sender;
// MyCell.m
#implementation MyCell
#synthesize rootViewController = _rootViewController;
-(IBAction)checkBoxClicked:(UIButton*)sender
{
[self setCheckBoxChecked:!_checkBoxChecked];
[_rootViewController refreshVisibleViewForCellTagged:self.tag];
}
In my cell I have a button that changes a variable and then calls a function in my rootViewController. The method is actually called however when I try to access any object in the RootViewController inside of the refreshVisibleViewForCellTagged method they are are '0x0' / nil;
// RootViewController.h
#interface RootViewController : UIViewController <UITableViewDataSource, UITableViewDelegate>
#property (nonatomic, strong) IBOutlet UITableView *myTableView;
// RootViewController.m
- (void) refreshVisibleViewForCellTagged:(NSInteger)cellTag
{
UITableView *tableView = self.myTableView; // nil
NSIndexPath *indexPath = [self.myTableView indexPathForSelectedRow]; // nil
MyCell *selectedCell = (MyCell*)[self.myTableView cellForRowAtIndexPath:indexPath]; // nil
if (selectedCell.tag == cellTag) {
NSLog(#"Refresh one way.");
} else {
NSLog(#"Do something else.");
}
}
Can anyone shed some light as to why I cant access any objects/variables in the RootController from within the method 'refreshVisibleViewForCellTagged'?
Please and thank you!
** My big question is Why can't I access any objects when calling a method in a view controller From a different view controller. There is some great programming truth that I am not aware of here, is it a permissions issue? Im not using #class (forward classing) in this instance.
As #trojanfoe said, delegation is a better way to do it.
Instead of #import "RootViewController.h", it is better to adop delegation. Because UITableViewCell is a child and RootViewController is the parent view. You don't want the child to talk directly with the parent.
To adopt delegation:
in MyCell.h file
remove #import "RootViewController.h".
revise MyCell.h as follows:
#protocol MyCellDelegate; // if you need to have forward declaration
#interface MyCell : UITableViewCell
// #property (nonatomic, strong) IBOutlet RootViewController *rootViewController;
#property (nonatomic) id <MyCellDelegate> delegate;
#end
#protocol MyCellDelegate <NSObject>
- (void)refreshVisibleViewForCellTagged:(NSInteger)cellTag;
#end
in MyCell.m.
#synthesize delegate;
-(IBAction)checkBoxClicked:(UIButton*)sender {
[self setCheckBoxChecked:!_checkBoxChecked];
//[_rootViewController refreshVisibleViewForCellTagged:self.tag];
[self.delegate refreshVisibleViewForCellTagged:self.tag];
}
in RootViewController.h adopt the delegation of MyCell
#import "MyCell.h"
#interface RootViewController : UIViewController <MyCellDelegate>
in RootViewController.m.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = // your implementation
//assuming all your cells are of MyCell kind
// set RootViewController as the delegate of each cell
((MyCell *)cell).delegate = self;
return cell;
}
implement the delegate method in RootViewController.m.
- (void)refreshVisibleViewForCellTagged:(NSInteger)cellTag {
// whatever you have
}
P.S. The above codes are for illustration. I didn't run them. If some part doesn't work, let me know, and I'll revise it.
The reason those objects in RootViewController are nil in the way you call, is because you are not accessing the same instance of RootViewController. It is a different (new) instance and hence all objects are nil.
Ignore the fact that view controllers are even involved. What you have are OBJECTS, connected together in a certain pattern. Accessing data in another view controller is no different from accessing data in any other object. There's no "magic" with view controllers, other than they have a few standardized connections to other objects.
IMHO, this is a poor design. For starters, your cell shouldn't need a reference to the view controller that the table it's in is in (read that twice, it barely makes sense just because the very idea of it is confusing). You have a strong reference to this view controller. So what happens when the OS tries to deallocate your view controller? It will never be able to, because the table view cell as a strong reference to it, keeping its retain count at 1. The same situation holds true for the cell. You risk running into a retain cycle here. Generally, child views should have weak references to their parents.
But this isn't even really a true parents/child relationship. I would suggest instead an approach like this, which all occurs in your view controller that contains the table view:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
// Assuming you set a reuse identifier "cellId" in the nib for your table view cell...
MyCell *cell = (MyCell *)[tableView dequeueReusableCellWithIdentifier:#"cellId"];
if (!cell) {
// If you didn't get a valid cell reference back, unload a cell from the nib
NSArray *nibArray = [[NSBundle mainBundle] loadNibNamed:#"MyCell" owner:nil options:nil];
for (id obj in nibArray) {
if ([obj isMemberOfClass:[MyCell class]]) {
// Assign cell to obj, and add a target action for the checkmark
cell = (MyCell *)obj;
[cell.checkMarkButton addTarget:self action:#selector(checkPressed:) forControlEvents:whateverEventYouWant];
break;
}
}
}
// Set the tag of the cell here, since we may get a different cell back from the reuse queue
cell.checkMarkButton.tag = indexPath.row;
return cell;
}
Now set up the method for the clicking of the checkmark button
- (void)checkPressed:(id)sender {
UIButton *checkmark = (UIButton *)sender;
// This will give you the row of the checked button
int checkedCellRow = checkmark.tag;
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:checkedCellRow inSection:0];
// Now you can grab a reference to that cell if you need to
MyCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
}
This way, you keep all of the controller-related stuff in your controller class (i.e. how to handle the checkmark button being pressed), and you don't need to deal with this whackiness of referencing the view controller of your cell's table.
EDIT: I guess I should also help answer your questions...First of all, if you're saying that in your refreshVisibleViewForCell method, you're getting a nil value for self.myTableView, are you sure it is hooked up properly in IB? Even if it's hooked up, click the little x to unhook it and hook it up again to be sure. Also make sure you've #synthesized your myTableView property. Without seeing more code, an IB issue is my best guess as to why you're getting a nil value for tableView. A nil value here will result in a nil indexPath and selectedCell, also. As for your big question, you can access properties of objects within your view controller. Those properties can, of course, be objects. So in your example, if you have a tag property on selectedCell, you can access it from anywhere that you have a valid reference to selectedCell. If selectedCell is nil, the property will be nil. #class is better suited for header files. For instance, if you wanted to make your custom cell a property of your view controller, you might say:
#import <UIKit/UIKit.h>
#class MyCell;
#interface RootViewController : UIViewController
#property (nonatomic, strong) MyCell *cell;
#end
Then, in your implementation file, you would actually import MyCell.h. Giving the #class forward declaration just keeps you from having to import all of the details about the MyCell class in your header file. The header doesn't need to know about all of the properties and methods of MyCell, just that you intend on using it in the implementation file. So you #class in the header, #import in the implementation.
in RootViewController.h:
#interface RootViewController : UITableViewController <UITableViewDelegate>
in RootViewController.m:
- (void) refreshVisibleViewForCellTagged:(NSInteger)cellTag {
NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
MyCell *selectedCell = (MyCell*)[self.myTableView cellForRowAtIndexPath:indexPath]; // nil
etc...
I'm not seeing declarations of myTableView in your RootViewController. But if your RootViewController implements UITableViewController, you can use self.tableView to access the tableview. You don't need to keep a reference to it by yourself.
#RachelD, if your RootView is more complicated than just a UITableViewController consider using a separate class, such as RootTableViewController. Then in your RootView xib, create IBOutlet for RootTableViewController to reference it. Like this:
// RootTableViewController definition
#interface RootTableViewController : UITableViewController
{
}
// RootViewController definition
#interface RootViewController : UIViewController
{
RootTableViewController *table_c;
}
#property (nonatomic, retain) IBOutlet RootTableViewController *table_c;
Note that you need to drag an "Object" into the "Objects" section (for RootViewController) in the interface builder, and type RootTableViewController in the Custom Class section for this object. Right click this object, make sure its IBOutlet, view, 2 delegates are correctly set.
The reason why your myTableView is nil is because it's not properly initialized. I mean, if you don't use UITableViewController you are responsible for assigning it manually via interface builder or something.
I am just curious. In IB, we can put a tableviewcontroller. However, as far as I know, we always subclass that tableview controller right? That way we can implement delegate, etc.
However, it seems that for some "default" behavior, IPhone intended tableviewcontroller to be used as is. Otherwise, why would IB let us put tableViewController like that?
Are there any sample code where people use tableViewController without subclassing?
Where does they implement things like what cells to draw, etc. then?
I guess the right answer of the question is that it's simply ridiculous to use a UITableViewController without sub classing. No body is doing it. Please correct me if I am wrong. I am just curious.
Whether you use a subclass of UITableViewController or UIViewController you need to set the data your table is going to display, otherwise, what's the point of a blank table? To achieve that you have to subclass and implement some methods. It's also a good idea to keep the delegate and the datasource in the same controller, unless the complexity really asks for different classes.
That being said, I always create my own table controllers as a subclass of UIViewController and implement the table controllers methods myself, because it gives you more flexibility. Matt Gallagher has several posts on how and why. See UITableView construction, drawing and management (revisited).
If you want to give it a try, create a subclass of UIViewController with a XIB and add the following sample code:
// interface
#import <UIKit/UIKit.h>
#interface SettingsVC : UIViewController <UITableViewDelegate, UITableViewDataSource>
#property (nonatomic, retain) IBOutlet UITableView *tableView;
#property (nonatomic, retain) NSMutableArray *array;
#end
// implementation
#synthesize tableView = _tableView;
#synthesize array = _array;
# pragma mark - UITableViewDataSource
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [self.array count];
}
- (UITableViewCell *)tableView:(UITableView *)aTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
int row = [indexPath row];
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [aTableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
cell.textLabel.text = [self.array objectAtIndex:row];
return cell;
}
Then add a UITableView object to the XIB, link the tableView of the controller to the UITableView object, and link the delegate and datasource of the UITableView to the controller.
No, this is not necessary to inherit your class with tableViewController. You can use table view by simply
putting TableViewController in xib.
and setting its delegate and datasourse to file's owner you can draw the table cells.
I don't think you can use a UITableViewController as is, it's like using a UIViewController without subclassing it : you can't set any inner mechanics.
But you can have a UITableView without using a UITableViewController.
Sure you can use UITableViewController without subclassing it.
Samplecode is very easy and straight forward.
For example like this:
- (IBAction)selectSomeOption:(id)sender {
UITableViewController *tableViewController = [[UITableViewController alloc] initWithStyle:UITableViewStyleGrouped];
tableViewController.tableView.dataSource = self;
tableViewController.tableView.delegate = self;
tableViewController.title = "Select some option";
[self.navigationController pushViewController:tableViewController animated:YES];
}
and the UITableViewDatasource and Delegate methods go into the same class.
Sure, if you like pain you could create a UIViewController in code and add a tableView on your own.
Or create a subclass for such an easy task.
The use of a non subclassed UITableViewController is sometimes convenient.