I have the following code:
- (CGFloat)tableView:(UITableView *)_tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
PostTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"Cell"];
return cell.imageView.frame.size.height + 40;
}
What I want to do is be able to access the cell's properties somehow. I want the cell's height to be equal to the height of the image in the cell's image view. I don't think this is working.
Don't try to access the cell. Your table's data source or some other object besides your cell should be managing that image. Ask that object for the image and take its size.
Treating your cell as a data container is tangling up your model, view, and controller layers and is likely to make changes more difficult down the line.
Related
I have setup the auto-sizing cells with UILabels with no problem in iOS8 following this tutorial:
http://useyourloaf.com/blog/2014/08/07/self-sizing-table-view-cells.html
But I am having problems setting up a UIImageView using auto-sizing. I need the images to be different sizes in Landscape compared to portrait (so they retain the same aspect ratio). But each time I get a broken layout constraints error
"<NSLayoutConstraint:0x14554680 'UIView-Encapsulated-Layout-Height' V:[UITableViewCellContentView:0x14564440(200)]>
As the actual code has quite a few different types of cell (that all work with auto-sizing cells) I have setup a simple example of the issue with a blue image view here:
https://github.com/AdrianMW/ios8autosizingCells
I have setup the constraints to the superview and am setting up the height like so:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
ImageTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:kImageCell forIndexPath:indexPath];
cell.heightConstraint.constant = [self heightForOrientation:self.interfaceOrientation];
return cell;
}
Solutions Tried
I have tried turning off setTranslatesAutosizingMask: on the cell as per some of the other suggestions but when I do I just get a blank space instead of a image. I have also tried adding the following:
[cell setNeedsDisplay];
[cell layoutIfNeeded];
I have seen mention of overriding sizethatfits: to get it to work on this cell using the old way but that doesn't seem to be called on the cell.
Cheers
In your ImageTableViewCell.xib, try changing the constraint:
Image View.Bottom EQUAL Superview.Bottom
Change the priority from 1000 to 999.
I am curious as to the behavior of the reuse identifier system.
I am working with a uitableviewcell that has two different uilabels on them.
Label one is always there and is updating correctly,
Label two starts with .alpha=0 and appears on a certain condition within the specific cell.
Label one is acting as suspected,
Label two acts strangely, when I first load the scene(viewdidload) it appears as it should.
When I scroll down and find a uitableviewcell has the labeltwo with .alpha=1 because it satisfied the conditional.
Up to this point everything is working, but now if I scroll back up, all label two's have an .alpha=1.
After doing some research, I have come to the conclusion that this has to do with me redefining what the reuse identifier cell template actually looks like programatically.
My question is , is there a way to reset the "buffer" to the uitableview cell i have created in storyboard that DOESNT have the changes I have made programatically.
Also since these are my own deductions, I may be incorrect in my assumptions,
Thanks for your time.
Your cells begins .alpha = 1, because of reuseIdentifier, that already see .alpha = 1, and set another sell to this parameter. As a first decision, you can control .alpha parameter for the each cell individually.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"FeedbackCell";
VZDetailFeedbackTableViewCell *cell = (VZDetailFeedbackTableViewCell *)[self.p_tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil)
{
cell = [[VZDetailFeedbackTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
// There can be more cells with Identifier
CGFloat alpha = 1.0f;
//if (something)
{
alpha = 0.0f;
}
[cell setSellAlpha:alpha];
}
// In your custom cell class you make method setAlpha and there control visibility
I've searched SO and have not seen an answer specifically for Autolayout.
I have a UITableViewCell using Autolayout. The UIImageView is constrained to have its edges 12 pt from Cell edges and the trailing edge of the Label.
Images are retrieved asynchronously and assigned to the UIImageView's image property.
[self downloadImageWithURL:[NSURL URLWithString:imageUrlString] completionBlock:^(BOOL succeeded, UIImage *image) {
if (succeeded) {
weakSelf.newsImageView.image = image;
// [weakSelf.contentView layoutIfNeeded];
}
}];
If there is a blank placeholder image assigned to the image of the cell in cellForRowAtIndexPath, then the asynchronously retrieved image is loaded and visible. If the blank placeholder assignment is commented out, the asynchronously retrieved image never appears.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
SCTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:tableCellIdentifier];
// cell.newsImageView.image = _blankImage;
return cell;
}
I tried layoutIfNeeded (commented out above) and updateConstraintsIfNeeded to see if the image would appear but it did not work. So for now I've been putting a blank image there first, which seems like a hack, and wouldn't be flexible if relying on intrinsic content size of images who's sizes could be different. Are the constraints being optimized out of existence when the first layout occurs? Anyone know what's going on and how to resolve it?
Try calling: invalidateIntrinsicContentSize on your UIImageView in the completion handler. This should force the auto layout system to recalculate the view intrinsic size. Possibly, you could also need calling updateConstraintsIfNeeded after that (but try first without).
If this does not work and your UIImageViews have a known size, you could try subclassing UIImageView and override the -intrinsicContentSize method. Return the known size from it.
Turns out the nib somehow had two outlets referring to the same UIImageView element. One outlet didn't exist in code, yet still linked in the nib UI. Must have been a mishap in refactoring, but removing it fixes it.
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 am using customcell with label. How to change the textcolour of label when the cell selected .By default it is black after selecting that, it needs to be white. How to do that in customcell point. Anyone help me.
Thanks in advance.
Try this code(I presume that you have an access to that label, right?):
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
yourLabel.textColor = //Your color;
}
You have to take one integer. when you select the cell assign the row value to that integer and reload the table view. in cellForRowAtIndexPath method out the code like
if(selectedIndex == indexpath.row){
textLabel.textColor = [UIColor whiteColor];
}
selectedIndex is a integer value
try out I am not tested but it may be working
In the custom cell xib .I have connected the label to the customcell.i just changed the text colour and highlighted text colour in the xib .and it is working great.