Following on from my last question, I have a tableview populated with 2 NSMutableArrays, 2 sections and 2 section headers, all of which are working ok.
incompleteItems = [NSMutableArray arrayWithObjects: #"Item 1", #"Item 2", #"Item 3"... , nil];
completeItems = [NSMutableArray arrayWithObjects: nil];
I have set it up so that when a user swipes to the right, the cell accessory changes from disclosure to checkmark, and when swiping to the left changes from checkmark to disclosure. The gestures are achieved using handleSwipeLeft/Right methods.
What I'd like to do is when a user swipes to the right, the Item from the incompleteItems array is moved into the completedItems array, thus moving the item from the "Incomplete" section to the "Complete" section.
What would be the best way to achieve such a thing? My experience is limited so this is somewhat outside of my knowledge.
Any help appreciated as always.
You can simply add the object from one array to the other and then delete it immediately.
-(void)incompleteToCompleteAtIndex:(NSUInteger)index
{
[complete addObject:[incompleteItems objectAtIndex:index]];
[incompleteItems removeObjectAtIndex:index];
}
-(void)completeToIncompleteAtIndex:(NSUInteger)index
{
[incompleteItems addObject:[complete objectAtIndex:index]];
[complete removeObjectAtIndex:index];
}
Since this will only occur as a result of a UI action I assume that this will happen on the main thread and there will be no reason for locking.
Do you need a nice animation? Check out: deleteRowsAtIndexPaths:withRowAnimation: and insertRowsAtIndexPaths:withRowAnimation:. Make sure you wrap these calls with beginUpdates and endUpdates.
I don't know of an easy way to animate moving a cell from one tableView to another. I can imagine a method that requires you to do a 3-step animation manually, removing the cell (and adding it to a new view that floats in front of your whole view hierarchy), moving the new view to the destination location (you may need to do your own math to determine the screen coordinates of the destination) and finally an addition animation. You could use a dummy cell that is completely transparent and swap it in / out in the first and last pieces of the animation to give the tableview something to hold the place of your transferred cell.
Related
So, deleting a table view cell is pretty straight forward. You remove the object from the array, and reload the table views data. Now... I have a table view that is populated from an NSMutableDictionary rather than array (we need to because we are parsing data and storing it). Does anyone know how to delete a cell via this method? I've tried simply calling [tableView reloadData]; which surprisingly worked, but obviously created an endless loop. I do not like endless loops. Does anyone have any suggestions? I couldn't find any relevant information in my research.
This is some relevant code in the cellForRowAtIndexPath delegate:
if (![frString isEqual:#"COOL STUFF"] && [subString isEqualToString:#"COOL"]) {
NSLog(#"A COOL is showing where it shouldn't, and it's %#", subString);
//remove all cells starting with COOL
[myDictionary removeObjectForKey:[self.dictName objectAtIndex:row]];
[tableView reloadData];
}
Also, I'd rather hide the cell instead of permanently removing the info from the dictionary. Is this possible?
There are a few things you're doing wrong :
You shouldn't remove the rows in the cellForRowAtIndexPath, because that's called when the tableview wants to render. So you remove a row, and then it renders again, calls cellForRowAtIndexPath:,...
Either delete the rows, or reload the data. deleteRowsAtIndexPaths: deletes sets of rows with animation, reloadData reloads the whole tableView, so it cancels the animation, and deleteRowsAtIndexPaths: becomes pointlesss
Ensure that you return the proper numberOfRowsInSection: did you remove the data from your dictionary ?
I have six on-screen buttons whose titles need to correspond to six elements in an NSMutableArray, when the value in the array changes, I also need the title to change with it. I am having trouble figuring out how to create that constantly updating line to the button, I'm still quiet new to objective-c development as well as Xcode.
I also need to make sure that when there is no value at that particular index of the array, the button cannot be clicked on
here is an example of one of the buttons
- (IBAction)card1Pressed:(id)sender {
if (self.userHasEnteredFirstNumber) {
if (!self.userHasEnteredSecondNumber) {
self.secondNumber = [sender currentTitle];
}
}
else{
self.firstNumber = [sender currentTitle];
}
}
The end goal is to have the user press two buttons, then chose weather to add, subtract, multiply, or divide them. After they pick one of those four operations, the values that the buttons were assigned to in the array will be removed and replaced with whatever the new number is. So after they do this once there will only be 5 numbers left in the array, then 4, then 3..... and so on.
The numbers will be drawn and added to an NSMutable array titled currentHand
UPDATE: Using UIOutletCollection I linked the buttons to the method like this
the link to the picture is here "sorry about not being able to directly post it but new users must have a reputation of 10 before they can"
link to photo of declaration and implementation with interface-builder of IBOutletCollection
was this correct?
the code for the header file regarding the IBOutletCollection is as follows "please note that this has been connected to the six buttons I want to use it with in interface builder, a picture of it is shown above"
#property (nonatomic,retain) IBOutletCollection (UIButton)NSArray *buttonArray;
the code in the implementation file regarding the IBOutletController is as follows
# synthesize buttonArray = _buttonArray;
You want to use Key-Value observing, check out this from the Apple documentation:
https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/KeyValueObserving/KeyValueObserving.html#//apple_ref/doc/uid/10000177i
Okay okay, so essentially you have a 'Button'-Array, whose 'Caption' is served by a NSMutableArray, which can easily be changed around, correct?
Now, this is only how I'd do it, there may be better solutions out there, but here goes:
You need a 'change' interface, which is called EACH time, something happens to your NSMutableArray. For example (since I don't know WHAT exactly is in that array of yours):
- (void) ChangeArray:(int)IDofElement (NSString *)newValue {
[arr replaceObjectAtIndex:IDofElement withObject:newValue]; //Updates/Empties the indexed Element.
if(newValue != nil) {
[buttons[IDOfElement] setText:newValue];
}
buttons[IDOfElement].enabled = (newValue != nil); //Makes Button 'clickable'
}
Like this, each time the value inside that array of yours gets changed, the corresponding caption also gets updated. Of course you would need an array of the buttons for this to work, but I don't think that's the big problem.
Another possible solution: Save a reference to the button inside of the object that's stored in the array and whenever the value is changed, change the button's caption too.
Does this help? Mind you, this is not the 'perfect solution', but something I'd come up with.
Please also note, that this is just from the top of my head and probably faulty at some points. But it should be able to point you in the general direction.
I've been trying to work out how to use table views and I'm a little stuck if I'm honest. I wanted to use a tableview with a limited number of rows (say 50 max). It starts of empty, with 0 rows. Then I wanted to do something along the lines of:
[self logMessage:#"Waiting for response"];
Which inserts a new row at the bottom with the above text. If I do another call to this pseudo function:
[self logMessage:#"Server response received"];
It should insert yet another new row below the previous row, and ensure it is visible. Once the above limit of 50 is reached, and a new message is inserted, I wanted the oldest message to be removed. All of this would be scrollable, with the latest being visible by default.
Am I looking at the right thing to do this? Eventually, I was hoping to have this in a nice little drawer below the main window, which I can then toggle from the main menu if needed. But as I said, I can't work out how to use a table view properly, it doesn't seem to be as straight forward as other objects are.
Any example code would be greatly appreciated!
Since log viewer is a read-only application of a UITableView, the way you do it is rather straightforward once you understand the basics. Recall that table views rely on their data models to provide them with the correct information that needs to be displayed.
A data model for "the last fifty lines of log" could be as simple as an NSMutableArray: use insertObject:atIndex: to add lines, and removeLastObject to remove the "overflow" lines, like this:
NSMutableArray *logLines = [NSMutableArray array]; // <<== this goes into the init method
-(void) addLogLine:(NSString*)line {
[logLines insertObject:line atIndex:0];
while (logLines.count > 50) {
[logLines removeLastObject];
}
}
Now you can use logLines as your table's "model": the data provider can tell how many lines there are by looking at logLines.count; the content of each row in the table will be the object at the corresponding index in logLines, and so on. Take a look at the UITableView section of your favorite iOs tutorial for the "boilerplate code" that needs to be written in order to display array elements in a UITableView.
I'm trying to create a UITableView with dates, shouldn't be very exciting, I know. It starts around the current date, but the user should be able to scroll down (the future) and up (the past) as far as he/she wants. This results in a potentially infinite number of rows. So what's the way to go about creating this?
Returning NSIntegerMax as the number of rows already crashes the app, but even if it wouldn't, that still doesn't account for being able to scroll up. I could start half way of course, but eventually there's a maximum.
Any ideas how to do or fake this? Can I update/reload the table somehow without the user noticing, so I never run into a border?
SOLUTION:
I went with #ender's suggestion and made a table with a fixed amount of cells. But instead of reloading it when the user scrolls to near the edges of the fixed cells, I went with reloading the table when the scrolling grinds to a halt. To accomodate with a user scrolling great distances without stopping, I just increased the row count to 1000, putting the ROW_CENTER constant to 500. This is the method that takes care of updating the rows.
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
NSArray *visible = [self.tableView indexPathsForVisibleRows];
NSIndexPath *upper = [visible objectAtIndex:0];
NSIndexPath *lower = [visible lastObject];
// adjust the table to compensate for the up- or downward scrolling
NSInteger upperDiff = ROW_CENTER - upper.row;
NSInteger lowerDiff = lower.row - ROW_CENTER;
// the greater difference marks the direction we need to compensate
NSInteger magnitude = (lowerDiff > upperDiff) ? lowerDiff : -upperDiff;
self.offset += magnitude;
CGFloat height = [self tableView:self.tableView heightForRowAtIndexPath:lower];
CGPoint current = self.tableView.contentOffset;
current.y -= magnitude * height;
[self.tableView setContentOffset:current animated:NO];
NSIndexPath *selection = [self.tableView indexPathForSelectedRow];
[self.tableView reloadData];
if (selection)
{
// reselect a prior selected cell after the reload.
selection = [NSIndexPath indexPathForRow:selection.row - magnitude inSection:selection.section];
[self.tableView selectRowAtIndexPath:selection animated:NO scrollPosition:UITableViewScrollPositionNone];
}
}
The magic breaks when a user scrolls to the edge of the table without stopping, but with the table view bounces property disabled, this merely feels like a minor glitch, yet totally acceptable. As always, thanks StackOverflow!
You should establish a fixed number of cells and adjust your datasource when the user scrolls near the end of the tableview. For example, you have an array with 51 dates (today, 25 future and 25 past). When the app tries to render a cell near one of the borders, reconfigure your array and call reloadData
You might also have a look at the "Advanced Scroll View Techniques" talk of the WWDC 2011. They showed how you would create a UIScrollView which scrolls indefinitely. It starts at about 5 mins. in.
Two thoughts:
Do you really need a UITableView? You could use a UIScrollView, three screens high. If end of scrolling is reached, layout your content and adjust scrolling position. This gives the illusion of infinite scrolling. Creating some date labels and arranging them in layoutSubviews: should not be too much of an effort.
If you really want to stick to UITableView you could think about having two UITableViews. If scrolling in your first one reaches a critical point, spin off a thread and populate the second one. Then at some point, exchange the views and trigger the scrolling manually so that the user does not note the change. This is just some idea from the top of my head. I have not implemented something like this yet, but I implemented the infinite UIScrollView.
I answered this question in another post: https://stackoverflow.com/a/15305937/2030823
Include:
https://github.com/samvermette/SVPullToRefresh
SVPullToRefresh handles the logic when UITableView reaches the bottom. A spinner is shown automatically and a callback block is fired. You add in your business logic to the callback block.
#import "UIScrollView+SVInfiniteScrolling.h"
// ...
[tableView addInfiniteScrollingWithActionHandler:^{
// append data to data source, insert new cells at the end of table view
// call [tableView.infiniteScrollingView stopAnimating] when done
}];
This question has already been asked: implementing a cyclic UITableView
I'm copying that answer here to make it easier because the asker hasn't ticked my answer.
UITableView is same as UIScrollView in scrollViewDidScroll method.
So, its easy to emulate infinite scrolling.
double the array so that head and tail are joined together to emulate circular table
use my following code to make user switch between 1st part of doubled table and 2nd part of doubled table when they tend to reach the start or the end of the table.
:
/* To emulate infinite scrolling...
The table data was doubled to join the head and tail: (suppose table had 1,2,3,4)
1 2 3 4|1 2 3 4 (actual data doubled)
---------------
1 2 3 4 5 6 7 8 (visualizing joined table in eight parts)
When the user scrolls backwards to 1/8th of the joined table, user is actually at the 1/4th of actual data, so we scroll instantly (we take user) to the 5/8th of the joined table where the cells are exactly the same.
Similarly, when user scrolls to 6/8th of the table, we will scroll back to 2/8th where the cells are same. (I'm using 6/8th when 7/8th sound more logical because 6/8th is good for small tables.)
In simple words, when user reaches 1/4th of the first half of table, we scroll to 1/4th of the second half, when he reaches 2/4th of the second half of table, we scroll to the 2/4 of first half. This is done simply by subtracting OR adding half the length of the new/joined table.
Written and posted by Anup Kattel. Feel free to use this code. Please keep these comments if you don't mind.
*/
-(void)scrollViewDidScroll:(UIScrollView *)scrollView_
{
CGFloat currentOffsetX = scrollView_.contentOffset.x;
CGFloat currentOffSetY = scrollView_.contentOffset.y;
CGFloat contentHeight = scrollView_.contentSize.height;
if (currentOffSetY < (contentHeight / 8.0)) {
scrollView_.contentOffset = CGPointMake(currentOffsetX,(currentOffSetY + (contentHeight/2)));
}
if (currentOffSetY > ((contentHeight * 6)/ 8.0)) {
scrollView_.contentOffset = CGPointMake(currentOffsetX,(currentOffSetY - (contentHeight/2)));
}
}
P.S. - I've used this code on one of my apps called NT Time Table (Lite). If you want the preview, you can check out the app: https://itunes.apple.com/au/app/nt-time-table-lite/id528213278?mt=8
If your table can sometimes be too short, at the beginning of the above method you can add a if logic to exit when data count is say for example less than 9.
My iPad app features a UITableView populated from a feed. Like most RSS readers, it displays a list of links to blog posts in reverse chronological order, with their titles and a summary of each post. The feed updates frequently, and is quite large, around 500 posts. I'm using libxml2 push parsing to efficiently download and parse the feed in an NSOperation subclass, constructing entry objects and updating a database as I go. But then I need to update the UITableView with changes.
So far, the app has been updating the UITableView for every post parsed, as it is parsed. The parser performs a selector on the main thread to do this work. But this leads to some serious lag for a couple of seconds if a lot of cells need to be updated. I can mitigate this by running the table update on a background thread, but it seems that this is not a good idea. So now I'm trying to figure out how to update the table more efficiently on the main thread.
I could just call reloadData when all the posts have been parsed, but it's not very user friendly: there's no animation to indicate that anything has changed, just a flash and the new data is there. I'd much rather have it animate to show that new posts are added and old posts removed. Existing posts that are not removed from the feed should be pushed down the table by the new posts appearing at the top.
I know this is possible. Byline, to give one example, does a beautiful job. Each post is added or removed from the UITableView one-at-a-time with no gaps showing the table background. All without making the UI in the least bit unresponsive. How is that done??
My latest attempt is to update the table only after all the posts have been parsed (the parser is quite fast, so it's not much of a delay). It then loads the existing posts in an NSDictionary mapping their IDs to their indexes in the array used as the table data source. It then iterates over every object in the newly-parsed array of posts, adding NSIndexPath for each to arrays that are later passed to -insertRowsAtIndexPaths:withRowAnimation:, -deleteRowsAtIndexPaths:withRowAnimation:, and -reloadRowsAtIndexPaths:withRowAnimation: as appropriate to insert, remove, move, or update cells. For 500 posts, this takes around 4 seconds to update, with the UI completely unresponsive. That time is used almost exclusively for the UITableView animated updates; iterating over the two arrays of posts takes very little time.
I then modified it so that those are updated without animation, and I have separate arrays to insert/delete/reload with animation only for row positions corresponding to currently-visible rows. This is better, but gaps appear as posts are removed and new ones added.
Sorry this is so long-winded, but here's the upshot:
How can I update a UITableView, with new cells pushed on, others pushed off, and still others moved from one position to another, with up to 500 cells in the UITableView (6-8 are visible at one time), and each animation happening in sequence, all while the UI remains completely responsive?
This question actually has three answers. That is, there are three parts to this question:
How to keep the UI responsive
How to keep the updating fast
How to make table update animation smooth
UI Responsiveness
To solve the first problem, I now make sure that no more than one table-updating message can be delivered on each iteration of the main event loop. That prevents the main thread from locking up if the background thread is feeding it stuff to do faster than it can cope with it.
This is done thanks to example code sent to me by Byline author Milo Bird, which I then integrated into Dave Dribin's DDInvocationGrabber. This interface makes it super easy to queue a method to be invoked on the next available iteration of the main event loop:
[[(id)delegate queueOnMainThread]
parserParsedEntries:parsedEntries
inPortal:parsedPortal];
I quite like how easy it is to use this method. The parser now uses it to call all of the delegate methods, most of which update the UI. I've released this code on GitHub.
Performance
As for performance, I was originally updating one UITableView row at a time. This was effective, but somewhat inefficient. I went back and studied the XMLPerformance example, where I noticed that the parser was waiting until it had collected 10 items before dispatching to the main thread to update the table. This was key to keeping the performance up without making the UI lock up by updating all 500 rows at once. I played around with updating 1, 10, and all 500 rows in a single call, and updating 10 seemed to offer the best tradeoff between performance and UI lockup. five would probably work pretty well, too.
Animation
And finally, there's the animation. Watching the “Mastering Table Views” WWDC 2010 session, I realized that my use of the deleteRowsAtIndexPaths:withRowAnimation: and updateRowsAtIndexPaths:withRowAnimation: methods was wrong. I had been keeping track of where things should be added and removed in the table and adjusting the indexes as appropriate, but it turns out that's not necessary. Inside a table update block, one only needs to reference the index of a row from before the update, regardless of how many may be inserted or deleted to change its position. The update block, apparently, does all that bookkeeping for you. (Go to about the 8:45 mark in the video for the key example).
Thus, the delegate method that updates the table for the number of entries passed to it by the parser (currently 10-at-a-time) now explicitly tracks the positions of rows to be updated or deleted from before the update block, like so:
NSMutableDictionary *oldIndexFor = [NSMutableDictionary dictionaryWithCapacity:posts.count];
int i = 0;
for (PostModel *e in posts) {
[oldIndexFor setObject:[NSNumber numberWithInt:i++] forKey:e.ident];
}
NSMutableArray *insertPaths = [NSMutableArray array];
NSMutableArray *deletePaths = [NSMutableArray array];
NSMutableArray *reloadPaths = [NSMutableArray array];
BOOL modified = NO;
for (PostModel *entry in entries) {
NSNumber *num = [oldIndexFor objectForKey:entry.ident];
NSIndexPath *path = [NSIndexPath indexPathForRow:currentPostIndex inSection:0];
if (num == nil) {
modified = YES;
[insertPaths addObject:path];
[posts insertObject:entry atIndex:currentPostIndex];
} else {
// Find its current position in the array.
NSUInteger foundAt = [posts indexOfObject:entry];
if (foundAt == currentPostIndex) {
// Reload it if it has changed.
if (entry.savedState != PostModelSavedStateUnmodified) {
modified = YES;
[posts replaceObjectAtIndex:foundAt withObject:entry];
[reloadPaths addObject:[NSIndexPath indexPathForRow:num.intValue inSection:0]];
}
} else {
// Move it.
modified = YES;
[posts removeObjectAtIndex:foundAt];
[posts insertObject:entry atIndex:currentPostIndex];
[insertPaths addObject:path];
[deletePaths addObject:[NSIndexPath indexPathForRow:num.intValue inSection:0]];
}
}
currentPostIndex++;
}
if (modified) {
[tableView beginUpdates];
[tableView insertRowsAtIndexPaths:insertPaths withRowAnimation:UITableViewRowAnimationTop];
[tableView deleteRowsAtIndexPaths:deletePaths withRowAnimation:UITableViewRowAnimationBottom];
[tableView reloadRowsAtIndexPaths:reloadPaths withRowAnimation:UITableViewRowAnimationFade];
[tableView endUpdates];
}
Comments welcome. It's entirely possible that there are more efficient ways to do this (the use of -[NSArray indexOfObject:] is particularly suspicious to me), and that I may have missed some other subtlety.
But even so, this is a huge improvement for my app. The UI now stays (mostly) responsive during a sync, the sync is fast, and the table update animation looks just about right.
Have you tried [tableView beginUpdates]; and [tableView endUpdate];?