I am trying to populate a TableView situated within a UIViewController with a collection of objects when a button is clicked.
The problem is that cellForRowAtIndexPath seems to be expecting 'votes' to be an instantiated object, which it isn't until the button is pressed.
I'm not sure I'm going about this the correct way and would appreciate any assistance anybody could give me.
I have specified the delegate and datasource as follows:
#interface MyViewController : UIViewController<UITableViewDelegate, UITableViewDataSource>
I have completed my implementation of numberOfRowsInSection as follows:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [self.votes count];
}
I have completed my implementation of cellForRowAtIndexPath as follows:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Votes";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
// Configure the region cell
CandidatePhrase *phrase = [self.votes objectAtIndex:indexPath.row];
cell.textLabel.text = phrase.phrase;
return cell;
}
On button press I'm loading an array with a list of objects
_votes = [[NSArray alloc] initWithObjects:myCandidatePhrase.votes, nil];
I'm just now clear on how the table will bind each time I press the button.
Here's the error I'm currently getting, presumably because the votes array hasn't been instantiated?
2011-12-09 22:34:48.979 MyApp[3809:fb03] -[NSObject tableView:numberOfRowsInSection:]: unrecognized selector sent to instance 0x6b49b20
The tableView instance (not the view controller) is going to call its delegate methods as soon as it is instantiated and whenever it is informed of a change to the table view. So it doesn't matter if votes is instantiated or not for the delegate method to be called.
However, if you want it to know that there are no rows when votes has not been instantiated, try this
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
if (votes != nil)
return [self.votes count];
else
return 0;
}
Once you have instantiated votes, you want to call reloadData on your tableView.
Don't forget to add your view controller as the delegate for the tableView, if it is not already.
Related
I have been implementing a app with sectioned UITableView. In the tableview, I used a array, called sections, to store different classes array and show them in different sections. On the other hand, I also used a array, called headers, to store section headers' name. For example, in the "weekday" section, there are seven words, Sunday to Saturday, in the tableViewCell under this section. In the MainViewController:
-(void)viewDidLoad
{
[super viewDidLoad];
NSMutableArray *weekday=[[NSMutableArray alloc]init];
NSMutableArray *traffic=[[NSMutableArray alloc]init];
for (NSArray *sec_ary in listData) {
NSString *class=[[sec_ary valueForKey:#"vocabulary_list"]valueForKey:#"Class"];
if ([class isEqualToString:#"WEEKDAY"]) {
[weekday addObject:[[sec_ary valueForKey:#"vocabulary_list"]valueForKey:#"Vocabulary"]];
}else if ([class isEqualToString:#"TRAFFIC TOOLS"]){
[traffic addObject:[[sec_ary valueForKey:#"vocabulary_list"]valueForKey:#"Vocabulary"]];
}
sections=[[NSArray alloc ]initWithObjects:weekday,traffic,nil];
headers=[[NSArray alloc]initWithObjects:#"WEEKDAY",#"TRAFFIC TOOLS",nil];
}
In this App, I also implemented the navigation controller, which can bring user to view detail information in the didSelectRowAtIndexPath method. The codes are following
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
AppDelegate *delegate = (AppDelegate *)[[UIApplication sharedApplication]delegate];
ContentViewController *content= [[ContentViewController alloc] initwithIndexPath:indexPath];
[delegate.navController1 pushViewController:content animated:YES];
[tableView deselectRowAtIndexPath:indexPath animated:YES];
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
static NSString *TableIdentifier = #"tableidentifier"; /
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:TableIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:TableIdentifier] autorelease];
}
cell.textLabel.text = (NSString*)[[self.sections objectAtIndex:indexPath.section]objectAtIndex:indexPath.row];
cell.textLabel.font = [UIFont boldSystemFontOfSize:15];
return cell;
}
In the ContentViewController:
-(void)viewDidLoad{
[super viewDidLoad];
AppDelegate *delegate=(AppDelegate*)[[UIApplication sharedApplication]delegate];
NSDictionary *voc_list=[delegate.vcblr objectAtIndex:index.row];
//extracting the voc_list dictionary to show infomation.....
}
I am wondering why each section will load the information from beginning in the voc_list. That is to say, the tableViewCell do not respond to the right detail content. Could anyone provide me with ideas to resolve it?
I am wondering why each section will load the information from beginning in the voc_list.
Because the code of your viewDidLoad method ignores index.section, paying attention to index.row alone. You need to decide on the index that you pass to delegate.vcblr based on both the section and the row; the exact calculation depends on the structure of your data, i.e. how many rows you have in each section.
Note : Using AppDelegate to share data among view controllers is not a good idea. Consider separating out your data in a separate model class, and make that class a singleton.
I have a UITableView backed by a NSArray.
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return self.data.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"CellIdentifier";
UITableViewCell *cell = [tv dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:CellIdentifier] autorelease];
}
id item = [self.data objectAtIndex:indexPath.row];
cell.item = item;
return cell;
}
Very standard. Now the problem is that reloadData will ask for numberOfSections and numberOfRows synchronously, but will call cellForRow asynchronously. So sometimes, by the time cellForRowAtIndexPath gets called, the data array has changed, and so [self.data objectAtIndex:indexPath.row] gets an out of bounds exception and crashes the app. How do I avoid this?
Note that every time I set the data array, I also call [self.tableView reloadData].
cellForRowAtIndexPath gets called frequently, (on scroll etc), you could just add a simple line of code to check if the size of the data array is smaller than the cell being requested. Although this means you might end up with blank cells.
I'd set breakpoints on both methods, right click the breakpoints -> "edit breakpoint" and tick "automatically continue after evaluating". Then click "add action" -> "debugger command" and then type "po data" or "po [data count]".
This will print information about the array in the debug console every time the breakpoint is hit (without stopping). You should then be able to look through the debug output and see where it is falling out of sync. Add some NSLog statements to to tell you which method is is being called etc and work from there.
I think the best way to avoid such a situation is to avoid user interaction while data is updated.May be you can show a screen to user that "updating.." and an activity indicator.
Another way is that to have another array to populate new data, handling can be done in separate thread and at times only it is assigned back to the datasource array with reloading call after that.There also a screen with same can be used while datasource array gets changed
Quick hack I used, try this and see if it works for you:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"CellIdentifier";
UITableViewCell *cell = [tv dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:CellIdentifier] autorelease];
}
// -----------------------------------------------------------------
// the magical line that prevents the table from fetching the data
// -----------------------------------------------------------------
if([indexPath row] < [self.data count])
{
id item = [self.data objectAtIndex:indexPath.row];
cell.item = item;
}
return cell;
}
:D
You should store a local array, that doesnt get modified. then, when your base array changes, you can update your storred array safely. Look into adding/removing cells from a table view using the built in api Add rows to existing UITableView section
I initiated a UITableView with the following code:
ProductTableView *tableProd = [[ProductTableView alloc]initWithNibName:#"ProductTableView" bundle:nil];
the xib file does exist!
Since I am displaying this table in a separate UIView I add it to this screen by:
[content addSubview:tableProd.view];
I used xcode to create a standard UITableView and set the following functions:
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return 10;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
cell.textLabel.text = #"test";
return cell;
}
The table is displayed in the simulator with 10 rows filled with test. However, when I start scrolling, and the first cell leaves the screen, the simulator crashes with a EXC_BAD_ACCESS error. I tried using Instruments to detect the NSZombie and the software flaged the zombie. Unfortunately I cant trace this error back to the cause.
Does anyone have a idea what is going wrong here?
if you're adding the view of a view controller as a subview of another view controllers view, i would guess that the ProductTableView view controller is being dealloced (since adding as a subview retains the view, but not the view controller it belongs to)
add the ProductTableView view controller as a property of the container view controller so that it is retained
So I've been given an assignment in my Mobile apps class: make a color game app for the iphone.(The description of how to game works is at the top of the pasted viewcontroller.h file below.)
I'm very new to Objective-C and cocoa, but have managed to troubleshoot and fix a lot of things in this app. The problem I have right now is that I don't know how to properly initialize and send UITableViewCells to the view. I'm confused because all of the tutorials I've found online use datasource methods to change different attributes of the UITableView and the cells as well. I'm not sure how these methods will interact with the controls I've already placed. I'm confused because I added them by the storyboard file, not by defining tableview attributes with datasource code.
My immediate issue is that my program won't display the proper text to the cells textlabel and detailtextlabel.
I've looked everywhere online for UITableView and UITableViewCell tutorials, but they are all from years ago and I'm not sure if the advent of the storyboard has changed the way I would treat these controls.
All of the code I've written is either in the viewcontroller.m or viewcontroller.h files.
The method within ViewController.m file, that should call the cell and display text and detail text:
-(IBAction)enterClicked
{
//On enter- send instance colors to the colorTable row[i], perform comparisons and append the resulting symbols to the instanceResults String. Send instanceResults string to the resultTable row[i]. When game counter reaches 6, gameOver. If on comparisons check, the instanceColors are the same as the gameColors, then the player wins.
[self checkForLoss];
if(!self.gameOver)
{
resultOfGuess = [self comparePlayerInputToGameColors:guessColors];
[listOfGuesses addObject:guessColors];
[listOfOutcomes addObject:resultOfGuess];
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:_numberOfTurnsPlayed inSection:0];
UITableViewCell *thisCell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:CellIdentifier];
thisCell.textLabel.text = [self.listOfGuesses lastObject];
thisCell.detailTextLabel.text = [self.listOfOutcomes lastObject];
[guessColors setString:#""];
if([self checkForWin:resultOfGuess])
[UpdateLabel setText:#"You have won!"];
else
[UpdateLabel setText:#""];
self.colorCounter = 0;
self.isStepOne = YES;
_numberOfTurnsPlayed++;
}
else
{
if([self checkForLoss])
[UpdateLabel setText:#"You have lost!"];
}
}
The UITableView DataSource Methods I've called at the bottom of the viewcontroller.m file:
#pragma mark - UITableViewDataSource protocol
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
if(section == 0)
return #"Guesses: Results:";
return 0;
}
-(NSInteger) numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
-(NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return 6;
}
-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if(cell == nil)
{
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:CellIdentifier];
}
return cell;
}
So my questions are: Can I change a control's properties with datasource methods, if I created the controls through the storyboard? How do I properly display the text in a uitableview's cells?
Edit/update: Thank you, I've used your advice jrturton, but now I've found something peculiar that may be the source of my problems. in my viewController.h file I've changed my header from
ViewController: UIViewController to ViewController: UITableViewController
Thinking that the datasource methods I call within the viewcontroller files have to be able to call the same methods and properties of the class that I call in the header-- Also, I see this done in other UITableView tutorial files.
The problem is that when I change the header to read-- ViewController: UITableViewController -- and I try to compile, I get this error:
Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[UITableViewController loadView] loaded the "2-view-3" nib but didn't get a UITableView.'
It compiles fine if I use just :UIViewController in the header file though.
Any ideas?
Further update: I''ve noticed within my storyboard that the only available ViewController object is a UIViewController object, while in the other tutorial files I've seen, this ViewController object is a UITableViewController object. I imagine this is my problem, but I can't seem to switch my UIViewController object to a UITableViewController. All I can do is create a new one, which isn't what I want, I imagine.
Your action method should update the data model (which I think it does, since it changes your listOfGuesses array). You then need to let your table view know that you have added or updated rows so that it can re-load them for you - check the UITableView documentation for reloading data or specific rows.
Creating a cell outside of the datasource methods isn't going to let that cell appear in your table.
At the moment I'm guessing you have 6 empty cells in your table view? You need to populate the text and detail labels in your cellForRowAtIndexPath method. The difference now there are storyboards is that you don't need to do the if (cell == nil) bit, as long as you have set the re-use identifier in your storyboard prototype cell then it will do all that for you. So your cellForRowAtIndexPath method can be reduced to:
-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath*)indexPath
{
// This will dequeue or create a new cell based on the prototype in your storyboard
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"Cell"];
// Put your actual configuration here based on your model array
cell.textLabel.text = #"Hello";
return cell;
}
Further hints (this is homework so I'm not giving full samples)
'indexPath.row` in the above method will give you the index from your model array that the cell refers to
You have defined the table as having 6 rows, but you are adding items to your model arrays as you go - so when the table asks for row 5, and your model only has 3 entries, you need to deal with this. Consider changing the number of rows in the table dynamically and using table view methods to indicate that new rows have been added. Again, see the UITableView documentation for this.
Typically the text is set in each cell by accessing the setText property:
[[cell textLabel] setText:#"static string"];
or
[[cell textLabel] setText:someNSString];
or with .dot notation
cell.textLabel.text = someNSString;
return cell;
BTW this is done in the method:
-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:
I think many of us has faced this problem on UITableView delegate method - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath which gets called twice.
In my application I transforming the tableView. The code is:
CGAffineTransform transform = CGAffineTransformMakeRotation(-M_PI/2);
theTableView.transform = transform;
theTableView.rowHeight = self.bounds.size.width;
theTableView.frame = self.bounds;
Now inside the delegate method I am doing a couple of things:
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath*)indexPath
{
modelRef.currentCellAtIndexPathRow = indexPath.row;
static NSString *CellIdentifier = #"Cell";
CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil)
{
cell = [[[CustomCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier frame:self.bounds] autorelease];
cell.selectionStyle = UITableViewCellSelectionStyleNone;
}
modelRef.currentPageIndex = (indexPath.row + 1);
[cell showPage];
NSLog(#" visible cell %i ",[[tableView visibleCells] count]);
return cell;
}
At a time 1 cell is visible, but first time when the application launches. The log shows visible cells 0.
Many a times this particular delegate method gets called twice abruptly.
How can I solve this?
I think an immediate fix is just to set a flag which changes the first time it is hit, so then you ignore the second call. It's probably not the perfect solution, and I can't tell you why it gets hit twice - but this will work. (I have experienced exactly the same behavior when I implemented an Apple delegate from the UIWebView class)
EDIT:
Create a BOOL member in the class header, then in the init set the value to be YES. So if the BOOL is called mbIsFirstCall for example, in your delegate method, do the following:
if (mbIsFirstCall)
{
// do your processing, then the line below
mbIsFirstCall = NO;
}
else
{
// you don't need this else, but just for clarity it is here.
// you should only end up inside here when this method is hit the second time, so we ignore it.
}