I have two UITableViews on one view and would like to implement the following logic:
- when a row is selected on tableView1 populate tableView2 with related information
I have set both UITableViews delegate and datasource, and am processing the initial population of tableView1 and didSelectRowAtIndexPath on tableView1. I am also checking to make sure the right UITableView is being handled i.e. tableView == MyTableViewVariable
Within handling didSelectRowAtIndexPath for tableView1 I finish off by calling [tableView2 reloadData] expecting that this would initiate the chain of method calls to force tableView2 to load up. But calling that method doesn't do anything.
A couple of posts indicate to me that people have got this working by putting a delay in their code, or forcing the call to be made from the main thread.
Can anyone point me to the best way to do this?
Cheers, James
use tags. But Its easier if you have two separate view controllers.
UITableView *a, *b;
a.tag = 0;
b.tag = 1;
- (void)tableView:(UITableView *)tv didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
if(tv.tag==0 && indexpath.row==0)
b.frame = CGRectMake(0,0,320,480);
[self.view addSubView:b];
[b reloadData];
}
Related
I have checked out every similar question and every answer,I have implemented with code. I have set
self.tableView.allowsMultipleSelection = NO;
self.tableView.allowsSelection = YES;
self.tableView.userInteractionEnabled = YES;
Check out the method name of what i expect of is didSelectRowAtIndexPath . There is
no UITapGestureRecognizer.UI Hierarchy shows nothing on the cell.
I have not implemented the method: willSelectRowAtIndexPath, shouldHighlightRowAtIndexPath, tableView:didDeselectRowAtIndexPath.
My custom cell is clean without xib.
Tapping the cell doesn't work ,but dragging the cell works and calls didSelectRowAtIndexPath.
Is there anyone know any other reason that can cause this bug?
wired! I have try take this UITableViewController into a demo and show, but in this demo it worked. Maybe some method in my project block didSelectRowAtIndexPath. How can find which method has blocked? How can I catch the tap event ,and find out which method has happened
If you are using UITableViewController inside a UIViewController, please check if you set the delegate & datasource of the UITableViewController or not.
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
check return height is correct. You can set cell backgroundColor to check cell frame.
I'm getting an EXC_BAD_ACCESS error when using scrollToRowAtIndexPath in the viewWillAppear method. I searched for solutions and saw some old posts recommending to set delegate and table to nil (see code below), however when I set that I simply dont get anything loaded in my tableview.
I should say that this is part of a chat application where I want to show the last message entered first. Many thanks for any assistance with this.
Here's my viewWillAppear:
-(void)viewWillAppear:(BOOL)animated {
[self.table reloadData];
int lastRowNumber = [self.table numberOfRowsInSection:0] - 1;
NSIndexPath* ip = [NSIndexPath indexPathForRow:lastRowNumber inSection:0];
//self.table.delegate = nil;
//self.table = nil;
[self.table scrollToRowAtIndexPath:ip atScrollPosition:UITableViewScrollPositionTop animated:YES];
}
I should add that this code seems to work fine in other parts of my program, the only time I get the error is in the viewWillAppear method.
viewWillAppear: is too early to do any animation on view. Per Apple Documentation:
This method is called before the view controller's view is about to
be added to a view hierarchy and before any animations are configured
for showing the view. You can override this method to perform custom
tasks associated with displaying the view. For example, you might use
this method to change the orientation or style of the status bar to
coordinate with the orientation or style of the view being presented.
If you override this method, you must call super at some point in your
implementation.
So, you cannot add animations when even the view hierarchy is not set completely.
It may help you
NSIndexPath * lastIndex =[NSIndexPath indexPathForRow:yourContenetArray.count-1 inSection:0];
[self.yourTableView scrollToRowAtIndexPath:lastIndex atScrollPosition:UITableViewScrollPositionNone animated:YES];
Write your code in viewDidAppear method.As your table view is loaded
then after you should call the method scrollToRowAtIndexPath . Then
your animation will be performed.And if you want to use in
viewWillAppear , then You can try to reload your tableView and then
write code for scrollToRowAtIndexPath
You should probably use the viewDidLoad method for scrolling, and if your array count is 0 (empty array) it will throw an error. It is not possible to scroll to cell at index -1.
I understand this might be covered in parts in answers to other questions (see references) I've seen on the site, but due to my limited experience I haven't been able to understand each part as it relates to my code. Please forgive me for any duplications.
I have a PFQueryTableViewController (essentially a UITableViewController) called threadsViewController that sources cell information from a Parse backend. The table view consists of threads similar to what you would see on a web forum.
I then have a separate class postsViewController which is another PFQueryTableViewController that I wish to display a table of all the responses ('posts') to that particular thread.
The functionality I'm looking for is for a user tapping on a thread (left screen in the image) to be presented with a postsViewController (right screen) containing only those posts/responses related to that thread. (See basic diagram below).
What I do know from my research:
The Parse backend is established with classes for Thread and Post.
I'm probably going to use the didSelectRowAtIndexPath delegate method
What I need help with:
How can I know which thread cell a user tapped on, and then pass that on so that the postsViewController only displays posts from that Thread?
A layman's description of how to use indexPath.row etc
I understand how to complete PFQueries etc to get the data for the cells, I just don't know how to implement the navigation and how to tell postsViewController which posts to show.
In case it helps somehow, here is my implementation so far. I have tried addign a property to the postsViewController called fromThread to somehow store the thread but apart from that I'm out of ideas!
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
[super tableView:tableView didSelectRowAtIndexPath:indexPath];
postsViewController *postsVC = [[postsViewController alloc] init];
postsVC.fromThread = //?
[self performSegueWithIdentifier:#"threadsToPosts" sender:self];
}
References
How to filter a Parse query by an tableview index?
Pass Index Number between UITableView List segue
didSelectRowAtIndexPath and prepareForSegue implementation
You're on the right track. You need know how to do two things: (1) access your parse objects by indexPath, and (2) push a new view controller in a navigation controller.
(1) is simpler: PFQueryTableVC provides a method called objectAtIndexPath: that does just what you need.
// indexPath is the indexPath parameter to the didSelectRow delegate method
PFObject *fromThread = [self objectAtIndexPath:indexPath];
(2) is simple, too. But more complicated because there are a couple ways to do it. Segue is the more modern way, but I think the old way is simpler, and certainly easier to describe in code. View Controllers are given storyboard ids on the "Identity" tab in the storyboard editor. Give your Posts-presenting VC a storyboard id like "PostVC".
To get a new instance, use that storyboard id as follows:
MyPostVC *postVC = [self.storyboard instantiateViewControllerWithIdentifier:#"PostVC"];
// initialize it with the PFObject we got above
postVC.fromThread = fromThread;
// present it on the navigation stack
[self.navigationController pushViewController:postVC animated:YES];
And fromThread is just what the PostVC will need to form a query for posts associated with the selected thread.
You can pass data of cell to next ViewController in prepareForSegue with something like this
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"threadsToPosts"]) {
UINavigationController *navCon = segue.destinationViewController;
postsViewController *postsViewController = [navCon.viewControllers objectAtIndex:0];
// Whatever you are populating your tableView with
Thread *thread = [self.thread objectAtIndex:self.tableView.indexPathForSelectedRow.row];
postsViewController.thread = thread;
}
}
I have an IOS application, which uses a UICollectionView for displaying a horizontal grid of cells. All i need, is a clever way of (lazy) loading data when the user reaches the end of my UICollectionView. The code i use now is :
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
GridCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:Cell forIndexPath:indexPath];
/**
TODO
- Find a good way to check if the user has reach the end of the grid
- This next piece of code is for demonstration purposes. A real check has to be
done yet!!!
**/
// releases is my datasource //
if(indexPath.row == (releases.count - 1)) {
[self getNextListData];
}
return cell; // <-- finally return the cell
}
The problem with this code is : if a user scrolls really fast to the end, he has to scroll back and forth to load more items. This is really not user friendly and i need a better way to load items when needed.
Does anyone have any suggestions?
Thanks in advance.
UICollectionView inherits from UIScrollView. UIScrollView has a delegate, UIScrollViewDelegate that has a bunch of methods related to scrolling. In one of these delegate methods (such as scrollViewDidBeginDecelerating:), you can check to see how far along the page you are, with the contentOffset and contentSize properties. If you're close to the end (defined by whatever % is the end for you), fetch more data.
An advantage to using a scrollview method is that it will not cause collectionView:cellForItemAtIndexPath: to be slower (by forcing it to run code for every collectionview unnecessarily).
This is basically the same technique that Apple suggests for lazy-loading of UITableView data's, applied slightly differently. They have some sample code for that as well (such as LazyTableImages)
When I ran into this problem with table views, I had to do some user testing. I found that if I started my load 10 cells before the end of the table, the new cell should be ready. Assuming that you are doing background loading of the data, that is.
if (indexPath.row >= [releases count] - 10)
[self getNextListData];
You would want to do some testing to see what number works for you.
In addition, I also had a loading indicator cell. In my number of rows in section callback, I always returned 1 extra.
return [releases count] + 1;
At the start of my cell for row callback I returned a special loading indicator cell.
if (indexPath.row == [releases count])
return [JLTActivityCell sharedInstance];
I'm not sure exactly how that advice will apply to collection views, but hopefully it gets you pointed in a good direction.
I have set up a demo application with a simple UITableViewController with no contents, but an 'Add' button in the toolbar. This launches a modal view controller which is again empty other than a 'cancel' button. The cancel button just tells its delegate (the UITableViewController) to dismiss the modal.
I then added an NSLog statement in the UITableViewController's numberOfSectionsInTableView method.
Ordinarily, when the table view controller loads I see two calls to numberOfSectionsInTableView. When I open and dismiss the modal (which returns to the UITableViewController) I see no further calls to numberOfSectionsInTableView.
However, if I return 0 from numberOfSectionsInTableView, in addition to the two calls on display, I also see an additional numberOfSections call when the modal is dismissed.
This only happens when numberOfSectionsInTableView returns 0, and I have added no additional code to my project besides that mentioned. This is easily verifiable by setting up a couple of controllers as I've described and modifying the result from numberOfSectionsInTableView.
My questions:
Why is the UITableView calling numberOfSectionsInTableView on return from a modal view?
Why is it only doing this if numberOfSectionsInTableView returns 0?
In addition to numberOfSectionsInTableView, the UITableViewController is also calling cellForRowAtIndex: when the modal is dismissed. In fact, it is attempting to display the new contents of its dataSource. How am I meant to manually animate a row insertion if the first row added is going to already be updated automatically? Shouldn't it be left to me to make sure that my UITableView is consistent with its dataSource?
What property is the UITableViewController checking to know that there is one or more sections (and therefore ask my delegate how many sections)? It can't be numberOfSectionsInTableView itself, since I would see it called whenever I return from the modal, not only when numberOfSections = 0.
From UITableViewController docs:
When the table view is about to appear the first time it’s loaded, the
table-view controller reloads the table view’s data... The
UITableViewController class implements this in the superclass method
viewWillAppear:
If you watch in the debugger, the second call upon app launch is from UITableViewController's viewWillAppear: implementation - specifically the part referred to above, where tableView is sent the reloadData message.
Now, the first call to numberOfSectionsInTableView: on launch is also from UITableViewController's implementation of viewWillAppear: but not directly from that implementation's call to -[UITableView reloadData]. I'm not sure what the first call is all about.
But, to your question, the call to numberOfSectionsInTableView: that happens when dismissing the modal has exactly the same call stack as the second call from applicationDidFinishLaunching:withOptions:. My hypothesis then is that UITableView interprets having zero sections as being in a state where it has not loaded at all. That does make some sense actually. I'd consider an "empty" table view to be one without any rows, but one without any sections seems almost "uninitialized" to me. Furthermore the UITableViewDataSource documentation implies UITableView has by default one section. Returning zero from this method would be inconsistent with that assumption of the docs as well.
Now, to your concern about animation - if you give the table an empty section to work with, you will be able to have full control over inserting the first row with whatever animation you'd like, and not be locked in to when you need to reload.
I think the moral of the story is, don't return zero sections unless you really, really need to for some reason. The title of your post refers to this table view being "empty" as well but I think it's clear the framework finds zero sections to not be empty but unloaded.
Hope this helps! And thanks for posting the sample project for me to play around with.
Perhaps the delegate just couldn't believe its eyes. But seriously, since a table view has to have at least one section, passing 0 doesn't make any sense. Why do it? You pass it an invalid argument and it gives you back a weird response. As to why it doesn't ask for number of sections when you pass 1, I think it's because it doesn't need to know at that point (coming back from the modal view controller) -- the table view has already been populated (if there were some data) and you haven't changed anything in the model, so it doesn't need to update.
I added a few lines to your example project to slide in a row each time you return from the modal view controller, which is what I think you're trying to do. I added an int property num for the return value of numberOfRowsInSection, added an array to populate the table, and a call to insertRowsAtIndexPaths from the modal view controller dismissal method.
- (void)viewDidLoad
{
_num = 0;
self.theData = #[#"one",#"two",#"three"];
[super viewDidLoad];
self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd
target:self
action:#selector(addRecipe)];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
NSLog(#"# sections requested");
//when 0, this fires on return from the modal. When 1, it does not.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSLog(#"in numberOfRows in section");
return _num;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"in cellForRowAtIndexPath");
UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:nil];
cell.textLabel.text = [self.theData objectAtIndex:indexPath.row];
return cell;
}
- (void)addRecipe
{
//create the modal and suscribe for delegate notifications
AddRecipeViewController *addRecipeController = [[AddRecipeViewController alloc]initWithStyle:UITableViewStyleGrouped];
addRecipeController.delegate = self;
//display the modal in a navigation controller
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:addRecipeController];
[self.navigationController presentModalViewController:navController animated:YES];
}
- (void)addRecipeVC:(AddRecipeViewController *)addRecipeVC didAddRecipe:(NSString *)recipe
{
[self dismissModalViewControllerAnimated:YES];
_num += 1;
[self performSelector:#selector(addRow) withObject:nil afterDelay:.5];
}
-(void)addRow {
[self.tableView insertRowsAtIndexPaths:#[[NSIndexPath indexPathForRow:_num-1 inSection:0]] withRowAnimation:UITableViewRowAnimationRight];
}
The tableview checks number of sections when it's populating the table view with data!
Since the table can be divided into sections, it has to know specifically how many sections to divide it into.
When you reload the data, the number of sections is also checked.
Because every time the table view has to take action in accessing either the data of the table, like what row you tapped, and in what section, or populating the data table, the number of sections has to be known!
Hope this helped!