I'm having a hard time understanding some of the logic behind the UITableView. I am populating my table from a MPMediaItemCollection as a queue of songs. What I am trying to achieve is to have a now playing indicator as the accessory view of the cell at the index path that matches the currently playing song.
I originally tried this with the following:
if (indexPath.row == [mutArray indexOfObject:[mainViewController.musicPlayer.nowPlayingItem valueForProperty:MPMediaItemPropertyTitle]]) {
UIImageView *playButtonView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"PlayButton.png"]];
[cell setAccessoryView:playButtonView];
}
This works fine for the now playing item, which is always actually objectAtIndex:0. But what I don't understand is why my table seems to define this index once every height of combined visible cells.
Let me try to explain this more clearly. Lets say that my table is 600px tall, and its content height is 1800px. This causes the indicator to be added roughly every 600px down the content height.
Now my first thought was that this was something wrong with the code for judging the index based off the name of the song, so I tried changing it to:
if (indexPath.row == 0)
But this produces the same result!
This screenshot should help explain what I'm talking about.
So, is there anything I can do to make the table treat indexPath0 as only the first cell in reference to the entire table instead of in reference to the currently visible cells?
You have to state explicitly also when the accessory should not be there:
if (indexPath.row==0) {
UIImageView *playButtonView = [[UIImageView alloc] initWithImage:
[UIImage imageNamed:#"PlayButton.png"]];
[cell setAccessoryView:playButtonView];
}
else {
[cell setAccessoryView:nil];
}
The reason is that when cell 0 gets dequeued (i.e. reused) on a different row it still has the accessory view in it.
Actually, this is a nice case study for understanding how dequeueing table view cells actually works ;-).
That's how tableview reuse cells: when cell scrolls out of screen it's added to reuse pool, so once you've added your accessory view to cell and that cell is reused - you'll see it in random places while scrolling.
You can check your cells index in -willDisplayCell:forIndexPath and add (if it's not added), hide (if it's there, but not your desired index) or show (if it's there and it's your index), or add accessory view to all cells and show/hide as needed.
Related
I've got a UIImageView to place a picture there and UITableView to place comments there. The part of the view with UIImageView should be scrolled with comment cells, that's why separate UIImageView and UITableView can't be used - the image won't be scrolled. If UIScrollView is used, than I receive scroll in scroll. Can cellForRowAtIndexPath method be used to create different cells? E.g.:
if (indexPath.row == 0) {
CellWithImage * cell = (CellWithImage *)[tableView dequeueReusableCellWithIdentifier:#"CellWithImage"];
//some code here
return cell;
}
else {
CellWithComment * cell = (CellWithComment *)[tableView dequeueReusableCellWithIdentifier:#"CellWithComment"];
//some code here
return cell;
}
For your case, its better to make the imageview part of the header view for the section
Yes, you can use different identifiers to load different cell types and use them together inside the same table. In fact, your case is somewhat simple -- you're only using a different cell for the first row. You could easily choose the cell type based on the type of data that will be displayed in the row, position of data within a hierarchy, etc.
I acknowledge that UITableview load dynamically a cell when user scrolls. I wonder if there is a way to preload all cells in order not to load each one while scrolling. I need to preload 10 cells. Is this possible?
You can initialize table view cells, put them into an array precomputedCells and in the data source delegate method tableView:cellForRowAtIndexPath: return the precomputed cells from the array instead of calling dequeueReusableCellWithIdentifier:. (Similar to what you would do in a static table view.)
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
return [self.precomputedCells objectAtIndex:indexPath.row];
}
It might also be useful to have a look at the
WWDC 2012 Session 211 "Building Concurrent User Interfaces on iOS"
where it is shown how to fill the contents of table view cells in background threads while keeping the user interface responsive.
I was looking for a solution to the original question and I thought I'd share my solution.
In my case, I only needed to preload the next cell (I won't go into the reason why, but there was a good reason).
It seems the UITableView renders as many cells as will fit into the UITableView frame assigned to it.
Therefore, I oversized the UITableView frame by the height of 1 extra cell, pushing the oversized region offscreen (or it could be into a clipped UIView if needed). Of course, this would now mean that when I scrolled the table view, the last cell wouldn't be visible (because the UITableView frame is bigger than it's superview). Therefore I added an additional UIView to the tableFooterView of the height of a cell. This means that when the table is scrolled to the bottom, the last cells sits nicely at the bottom of it's superview, while the added tableFooterView remains offscreen.
This can of course be applied to any number of cells. It should even be possible to apply it to preload ALL cells if needed by oversizing the UITableView frame to the contentSize iOS originally calculates, then adding a tableFooterView of the same size.
Hopefully this helps someone else with the same problem.
As suggested by Mark I also changed the height of my UITableView temporarily so that the table view creates enough reusable cells. Then I reset the height of my table view so that it stops creating reusable cells while scrolling.
To accomplish that I create a helper bool which is set to false by default:
var didPreloadCells = false
It is set to true when my table view first reloaded data and therefore created the first reusable cells.
resultsHandler.doSearch { (resultDict, error) -> Void in
[...]
self.tableView.reloadData()
self.didPreloadCells = true
[...]
}
The real trick happens in my viewDidLayoutSubviews Method. Here I set the frame of my table view depending on my boolean. If the reusable cells were not created yet I increase the frame of the table view. In the other case I set the normal frame
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
self.tableView.frame = self.view.bounds
if !didPreloadCells
{
self.tableView.frame.size.height += ResultCellHeight
}
}
With the help of that the table view creates more initial reusable cells than normal and the scrolling is smooth and fluent because no additional cells need to be created.
Change the dequeueReusableCellWithIdentifier when you are reusing the table view otherwise it will load the old data
Solution for autoresizing cells. Change 'estimatedRowHeight' to lower value
- (void)viewDidLoad {
[super viewDidLoad];
self.tableView.rowHeight = UITableViewAutomaticDimension;
self.tableView.estimatedRowHeight = 32; //Actual is 64
}
Actual estimated height is 64. 32 is used to add more cells for reuse to avoid lagging when scrolling begins
I have a timer which calls the below code to reload a cell in the second section of my grouped UITableView. It works perfectly fine unless I scroll the screen up so that the first section/cell cannot be seen. Once it "springs back" to its correct position, I see that the text which should appear in section 0 has appeared in section 1 and vice-versa.
[self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForRow:0 inSection:1]] withRowAnimation:UITableViewRowAnimationNone];
Does reloadRowsAtIndexPaths or cellForRowAtIndex path work from the top of the full (visible or invisible) cells, or does it only work starting on the cells that are visible on the screen? In other words, does section 0 actually change depending whether it is visible on-screen or not?
What else would cause cellForRowAtIndexPath to load the wrong data into the cells?
Ok, I played a bit with your project, here are my suggestions:
As you are adding the button to the cell, remember to remove it when you don't want use it (when you refresh the cell, basically you create a new cell, and store the second one to reuse, so if you scroll down and then up, you'll reuse that cell as the cell for the name).
if (cell == nil)
{
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
[[cell viewWithTag:2] removeFromSuperview];
for this to work, you must set the corresponding tag to the button:
myButton1.tag = 2;
[cell addSubview:myButton1];
And also, add the button directly to the cell, not to the contentView (this just worked for me, I'm not sure why).
EDIT: I uploaded a fixed version of your project, download it.
I making an app with a table view and a data source (core data). In this table i group several tasks ordered by date, and i have this segmented control.
I want the table to only load the tasks later or equal than today's date, when the user taps the second segment i want to show all tasks, if he taps the first segment the table must only show the later dates tasks again.
The problem is:
1 - I'm using fetchedResultsController associate with a indexPath to get the managed object.
2 - I use the insertRowsAtIndexPaths:withRowAnimation: and deleteRowsAtIndexPaths:withRowAnimation: methods to make the cells appear and disappear. And this mess with my indexPaths, if i want to go to the detail view of an specific row it is associate with a different indexPath, after delete the rows.
This problem was fixed by a method i did, but i still have other problems of indexPaths and cells, and it seems to me that is gone be me messy to each problem a fix.
There is a simple way to do that?
I tried just to hide the cells instead of delete, it works just fine, but in the place of the hidden cells was a blank space, if there is a way to hide these cells and make the non-hidden cells occupy the blank space i think that will be the simplest way.
Anyone can help me?
set the height of the cell to 0 when it hides, and set the height back to the original value when it appears.
TableViewController.h
#interface TableViewController{
CGFloat cellHeight;
}
TableViewController.m
- (void)cellHeightChange{
//if you need hide the cell then
cellHeight = 0;
cellNeedHide.hidden = YES;
//if you need hide the cell then
cellHeight = 44; // 44 is an example
cellNeedHide.hidden = NO;
}
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath;
{
switch (section) {
// for example section 0 , row 0 is the cell you wanna hide.
case 0:
switch (row) {
case 0:
return cellHeight;
}
}
}
When the user taps on a segment execute a new fetch request on your managed object to give you an appropriate array (either an array of all dates, or the greater/equal dates). Then use reloadData on the tableView using this new array in the datasource.
or
Give the cell's you wish to hide a height of 0?
I am currently working a on project where I have lots of custom table view cells. Part of the requirements is that the cells be able to expand if their default size can not hold all of the content. If they need to be able to expand I have to add a UIButton to the cell and when it is tapped redraw it in a bigger view where all the data fits. Currently in draw rect I essentially do this:
if([self needsExpansion]) {
[self addExpansionButton];
}
-(void)addExpansionButton {
self.accessoryButton = [UIButton buttonWithType:UIButtonTypeCustom];
[self.accessoryButton setShowsTouchWhenHighlighted:YES];
UIImage *buttonImage = [UIImage imageNamed:#"blue_arrow_collaps_icon.png"];
[self.accessoryButton setFrame:CGRectMake(280, 82, buttonImage.size.width, buttonImage.size.height)];
[self.accessoryButton setImage:buttonImage forState:UIControlStateNormal];
[self.accessoryButton addTarget:self action:#selector(toggleExpanded) forControlEvents:UIControlEventTouchUpInside];
[self addSubview:self.accessoryButton];
}
This works fine, except for when I click anywhere else in the cell the button flickers and disappears. Anyone know how to propertly do this?
From the UITableViewCell Class Reference:
You have two ways of extending the
standard UITableViewCell object beyond
the given styles. To create cells with
multiple, variously formatted and
sized strings and images for content,
you can get the cell's content view
(through its contentView property) and
add subviews to it.
Instead of adding the accessory button as a subview of the UITableViewCell, you should add it as a subview of the contentView:
[[self contentView] addSubview:self.accessoryButton];
Have you worked out the following problem in your design approach?: Let's say one of your cells (let's call it A) determines it needs expansion, so you add a button to it. What happens when the user scrolls through the UITableView? For performance reasons, your UITableView delegate should be using dequeueReusableCellWithIdentifier in tableView:cellForRowAtIndexPath:. So you'll be reusing A to display a different row of the table. Do you really want A to have an accessory button? Probably not, since it's now representing a different object.
You're probably better off doing the cell customization at the UITextViewDelegate. In tableView:cellForRowAtIndexPath:, you can determine if the object being displayed at the row specified needs a button, and if it does add it as a subview to the contentView.
Then again, if your table size is always relatively small (say < 50), you can use this approach Jeremy Hunt Schoenherr suggests.