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.
Related
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
Is it possible to load all cells of an UITableView when the view is loaded so that they are not loaded when I'm scrolling?
(I would show a loading screen while doing this)
Please, it's the only way at my project (sorry too complicate to explain why ^^)
EDIT:
Okay let me explain you, what I'm definite doing:
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSString *cellIdentifier = [NSString stringWithFormat:#"Identifier %i/%i", indexPath.row, indexPath.section];
CustomTableCell *cell = (CustomTableCell *)[tableView dequeueReusableCellWithIdentifier:cellIdentifier];
NSDictionary *currentReading;
if (cell == nil)
{
cell = [[[CustomTableCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier] autorelease];
UILabel *label;
UIView *separator;
if(indexPath.row == 0)
{
// Here I'm creating the title bar of my "table" for each section
}
else
{
int iPr = 1;
do
{
currentReading = [listData objectAtIndex:iPr-1];
iPr++;
} while (![[currentReading valueForKey:#"DeviceNo"] isEqualToString:[devicesArr objectAtIndex:indexPath.section]] ||
[readingresultsArr containsObject:[currentReading valueForKey:#"ReadingResultId"]]);
[readingresultsArr addObject:[currentReading valueForKey:#"ReadingResultId"]];
//
// ...
//
}
}
return cell;
}
My error happens in the do-while-loop:
"listData" is an array with multiple dictionaries in it.
My problem ist that when I’m scrolling my table slowly down, all is fine, but when I’m scrolling quickly to the end of the view and then I’m scrolling to the middle, I get the error that iPr is out of the array’s range. So the problem is, that the last row of the first section has already been added to the "readingresultsArr", but has not been loaded or wants to be loaded again.
That’s the reason why I want to load all cells at once.
You can cause all of the cells to be pre-allocated simply by calling:
[self tableView: self.tableView cellForRowAtIndexPath: indexPath];
for every row in your table. Put the above line in an appropriate for-loop and execute this code in viewDidAppear.
The problem however is that the tableView will not retain all of these cells. It will discard them when they are not needed.
You can get around that problem by adding an NSMutableArray to your UIViewController and then cache all the cells as they are created in cellForRowAtIndexPath. If there are dynamic updates (insertions/deletions) to your table over its lifetime, you will have to update the cache array as well.
put a uitableview on a uiscrollview
for example , you expect the height of the full list uitableview is 1000
then set the uiscrollview contentsize is 320X1000
and set the uitableview height is 1000
then all cell load their content even not visible in screen
In my case it was that I used automaticDimension for cells height and put estimatedRowHeight to small that is why tableview loaded all cells.
Some of the answers here and here suggest using automaticDimension for cells height and put mytable.estimatedRowHeight to a very low value (such as 1).
Starting with iOS 15 this approach seems not to work anymore. Hence, another way to achieve the table to "load" all cells could be by automatically scrolling to the last cell. Depending on the tables height and how many rows it can show some cells are discarded but each cell would be loaded and shown at least once.
mytable.scrollEnabled = YES;
NSIndexPath* indexPath = [NSIndexPath indexPathForRow:cellCount - 1 inSection:0];
[mytable scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];
mytable.scrollEnabled = NO;
If you want to scroll up again just scroll to the top as outlined here.
Following the comment that was made by juancazalla, I found that if you have a tableView that is using automaticDimension, loading all the cells at once can be best achieved by setting estimatedRowHeight to a low value (such as 1).
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.
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'm trying to mimic the address cell in Address Book / Contacts App.
I want a cell with style UITableViewCellStyleValue2 to display an address such as:
// 123 Fake St.
// Suite 555
// Denver CO, 80000
But actual cell isn't drawing the way I want. The label is drawing outside the bounds of the tableview row and part of top of the label is being cut off by the row directly above it.
Here's what I have so far:
cell.detailTextLabel.lineBreakMode = UILineBreakModeWordWrap;
cell.autoresizingMask = UIViewAutoresizingFlexibleHeight; //doesn't seem to do anything
self.tableView.rowHeight = 88.0f; // default is 44.0
cell.detailTextLabel.numberOfLines = 0; //unlimited lines
An NSLog statement confirmed the rowHeight is set to 88.0.
I realize a delegate method exists to change the row height. However, in my current app I only need this one cell to expand with the text, so I didn't feel it necessary to implement the delegate method.
Thank you for your help.
I don't think that setting row height this way (self.tableView.rowHeight = 88.0f;) for a single row will work. You should implement the delegate method which in your case is very simple, i.e.
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
return ([indexPath row] == MY_TALLER_CELL_ROW) ? 88.0f : 44.0f;
}
I think you'll probably have more luck not using the cell's default textLabel and detailTextLabel views; instead, create your own labels and add them to the cell's content view.