I'm using a UITableView control to show some data that can be edited by the user. To edit the details the user taps on an edit button which pushes a new view onto the stack. The user edits the data, taps a save button and the data is saved to a plist and the view popped off the stack. Even though the plist has been updated the UITableView still shows the old data. This can be corrected by adding a call to reloadData in the viewWillAppear method. However when the view is first loaded the data is displayed correctly, by adding the reload statement does this mean a double bind? If so, how can this be avoided?
I found the following code (here) which forces a refresh without explicitly calling reloadData:
- (void) viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
int orientation = [[UIDevice currentDevice] orientation];
if(orientation != UIDeviceOrientationUnknown)
[self willRotateToInterfaceOrientation:orientation duration:0];
}
Can anyone explain how/why this works?
The trick from your link is a dirty hack. Not only does it reload the data, but also forces the table to redraw. It tells your app that the device is getting a new orientation, so your table gets redrawn, along with other UI elements.
The standard way of refreshing a single row or a specific set of rows in your UITableView is calling its reloadRowsAtIndexPaths:withRowAnimation: method: doing so calls through to your data source to get data for only the row(s) that have been updated, preventing the full reload.
Do this:
- (void) viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
//remove all objects from yourTableViewDataSourceArray
[yourTableViewDataSourceArray removeAllObjects];
//add new records from plist
yourTableViewDataSourceArray = plist request of data here
//reload table now
[yourtableView reloadData];
}
Related
I have implemented pull to refresh in a table view that is a subview to my main view like so:
UITableViewController *tableViewController = [[UITableViewController alloc] init];
tableViewController.tableView = self.tableView;
self.refreshControl = [[UIRefreshControl alloc] init];
[self.refreshControl addTarget:self action:#selector(refresh:) forControlEvents:UIControlEventValueChanged];
tableViewController.refreshControl = self.refreshControl;
This updates the table and everything fine, the problem I'm having is when I touch the table to drag the cells seem to randomly shift up above the screen. This happens when I touch and drag from the middle of the screen down, or if I pull before the the cells shift back to their normal position. Here are some screen shots to better paint a picture. Keep in mind that all of these are taken after I drag down, yet the cells shift upward.
Should look like:
actually looks like these after the cells jump:
For anyone that may be having this issue or an issue like this I found a way to get the scroll to refresh to work very smoothly and not cause the issues I was having. I'm using an actual UITableViewController now instead of an embedded UITableView which helped with some of the scroll issues, but I still had an issue where instead of animating the closing of the refresh icon (table sliding up to cover the spinning circle) it just shut instantly and seemed very jarring. I put my refresh logic in the background, let it finish and then finished refreshing. My code structure is as follows:
- (void)viewDidLoad {
//set up refreshcontrol to call my refresh method
}
- (void)refresh {
[self performSelectorInBackground:#selector(getUpdatedInfo) withObject:nil];
}
Updated info runs and my TableViewController is a delegate of my class that gets refreshed information. When all the information is received and the update is completed I call the delegate method in my refreshing TableViewController class that puts the received array into the table, updates the table, and ends refreshing.
- (void)didFinishingUpdatingWithArray:(NSArray *)array {
//configure table sections
//Save the data
[self.tableview reloadData];
[self.refreshControl endRefreshing];
}
I have subclassed a CollectionView and using it using to display a collection of images in different categories. For example: Most Popular, Most Viewed. I access each category/page through a TabbarController.
The classes I have are:
Main class - MediaList - Base class for fetching and displaying media in a collection view depending on what type of media is requested.
SubClasses - MostPopular and MostViewed are both very light classes that inherit from the main class.
The problem is that when I move from MostPopular to MostViewed, the collection view initially displays the last category of pictures and then refreshes to the new...As a result you see a flicking effect.
Sample code from MediaList
- (void)viewDidLoad
{
[super viewDidLoad];
self.mediaCollection.dataSource = self;
self.mediaCollection.delegate = self;
[self getMedia];
}
(void) getMedia
{
NSLog(#"///////////////////////// GETTING MEDIA /////////////////////////");
XMLGenerator * sharedXmlGen = [XMLGenerator sharedXmlGenerator];
GlobalVars * sharedGlobalVars = [GlobalVars sharedGlobalVars];
sharedXmlGen.assetFlag = _contentFilter;
NSLog(#"The filter is: %#", _contentFilter);
[sharedXmlGen getPhotoVideoWithCallBackFunction:^{
[_mediaCollection performSelectorOnMainThread:#selector(reloadData) withObject:nil waitUntilDone:YES];
}];
}
Sample code from SubClass (MostPopular):
- (void)viewDidLoad
{
[super setContentFilter:FILTER_POPULAR]; //Set the filter for the type of content
[super viewDidLoad];
// Do any additional setup after loading the view.
}
Two clarifications:
I should add that I am trying to re-use as much code as possible without having to create new views on the storyboard or controllers.
Because the media returned is very dynamic and can be updated regularly, I have had to reload my data (using getMedia) on viewDidAppear. This now means each selection of a particular page will result in the flickering when the new view is loaded...
Updates
- After further investigation it looks like this has nothing to do with subclassing the uicollectionview. The issue instead is just reloading data into the uicollectionview. To be sure, I just clicked on one of the two subclassed views. I also added a reload method to the viewdidAppear method just to see the issue get even worse. It's also much easier to see that the issue is that last set of images in the collection view initially displays the last category of pictures before the new one refreshes. Then once the collection is refreshed I get the flicker.
*Updates Oct 4 *
Starting to think my best solution is to display a waiting indicator and block the page while loading. I did try setting the uicollectionview to nil, and believe that will solve the problem as well, but not sure it will be straightforward to reset.
Although it may not be immediately apparent in the code above the root cause was actually the getMedia call. All of the subclassing etc. works perfectly fine.
Specifically having the reload method in the getMedia call and was creating the issue.
[_mediaCollection performSelectorOnMainThread:#selector(reloadData) withObject:nil waitUntilDone:YES];
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!
This seems ridiculous but I can't seem to sort it out. I need to insert a row in a table view in response to a push notification. The implementation should be as simple as
- (void)didSaveMessage:(Message*)message atIndex:(int)index
{
//check to make sure I have an array to populate the table from...
if (self.messageManager.messages != nil)
{
self.indexRow = index;
NSLog(#"refresh table view from code");
//remove a label that says "You have no messages"...
[[messageTable tableFooterView] removeFromSuperview];
[messageTable beginUpdates];
[messageTable insertRowsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForRow:index inSection:0]]
withRowAnimation:UITableViewRowAnimationFade];
[messageTable endUpdates];
[self scrollToNewestMessage];
}
}
This method is called when I receive a remote notification and it does fire. The log statement prints. However, the UITableView does not update. What is particularly strange to me is that if I put the same code in an IBAction and link it to a refresh button in storyboard, it works. Is there something special that I have to do to update a UITableView programmatically?
Try to send the table the reloadData message. This should force the table view to update.
It seems pretty trivial, but is it possible that the Message* that you are passing into the didSaveMessage is nil? It would explain why the NSLog statement works, and I would assume that you had to create the message manually when testing from an IBAction.
This is resolved. I was calling the method to update the UI from didReceiveRemoteNotification: in the AppDelegate but to a different instance of my view controller. So I added a viewController property onto the app delegate, set the value for that in my view controller's view did load, and now it's all working.
I have a problem in my application. Any help will be greatly appreciated. Basically it is from view A to view B, and then come back from view B.
In the view A, it has dynamic data loaded in from the database, and display on the table view. In this page, it also has the edit button, not on the navigation bar. When user tabs the edit button, it goes to the view B, which shows the pick view. And user can make any changes in here. Once that is done, user tabs the back button on the navigation bar, it saves the changes into the NSUserDefaults, goes back to the view A by pop the view B.
When coming back to the view A, it should get the new data from the UIUserDefaults, and it did. I used NSLog to print out to the console and it shows the correct data. Also it should invoke the viewWillAppear: method to get the new data for the table view, but it didn't. It even did not call the tableView:numberOfRowsInSection: method. I placed a NSLog statement inside this method but didn't print out in the console.
As the result, the view A still has the old data. the only way to get the new data in the view A is to stop and start the application.
Both view A and view B are the subclass of UIViewController, with UITableViewDelegate and UITableViewDataSource.
Here is my code in the view A :
- (void)viewWillAppear:(BOOL)animated {
NSLog(#"enter in Schedule2ViewController ...");
// load in data from database, and store into NSArray object
//[self.theTableView reloadData];
[self.theTableView setNeedsDisplay];
//[self.theTableView setNeedsLayout];
}
In here, the "theTableView" is a UITableView variable. And I try all three cases of "reloadData", "setNeedsDisplay", and "setNeedsLayout", but didn't seem to work.
In the view B, here is the method corresponding to the back button on the navigation bar.
- (void)viewDidLoad {
UIBarButtonItem *saveButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemSave target:self action:#selector(savePreference)];
self.navigationItem.leftBarButtonItem = saveButton;
[saveButton release];
}
- (IBAction) savePreference {
NSLog(#"save preference.");
// save data into the NSUSerDefaults
[self.navigationController popViewControllerAnimated:YES];
}
Am I doing in the right way? Or is there anything that I missed?
When a view is first loaded, it calls the viewDidLoad method. If you create a stack, drill down into it (from A to B) and then return (B to A) the viewDidLoad does not get called again on A. What you may want to try is passing A into B (by passing in self) and call the viewDidLoad method to get the new data and then reloadData method on the the tableView to refill the table view.
What you may want to try is taking the data fetching and setting functionality out of the viewDidLoad method and place it in its own getData method. At the end of the getData method, you could place a [self.tableView reloadData]; to reset/refill the table view. From class B, you could call [self getData] and minimize the amount of work you would do in class B. This would help increase reuse-ability of that code and may prevent side effects from calling the viewDidLoad method.
You could also use viewDidAppear. It is called every time the screen appears. For performance reasons, set a flag so you don't repeat the same functionality in viewDidLoad with viewDidAppear for the first screen view.