UITableViewCell: Dynamic Cell Height by 'Cell Identifier' - ios

(note: The tableView I am using is from the Parse.com iOS SDK - PFQueryTableViewController)
Scenario = I have a TableViewController that has two different types of cells (each with their own identifier). Each object upon being queried and loaded into the datasource is checked if a key on the object is true. Depending on the result I dequeueReusableCellWithIdentifier to the correct cell.
-(PFTableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath object:(PFObject *)object {
myTableViewCell *cell;
if ([object[#"orientation"] isEqualToString:#"left"] || [object[#"orientation"] isEqualToString:#"right"]) {
myTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"Cell"];
else {
myTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"Cell2"];
}
This all does its job. Each cell is being loaded at the correct indexPath.row and everything. Problem is my tableView "Row Height" itself does not readjust for the new cell. This causes overlapping of cells and makes everything ugly. I can tell the tableView in storyboard to set the row height to whatever the larger of the two cell heights is, but that leaves big spaces in-between cells too which also makes it look ugly.
Question = It is my belief (and correct me if I'm wrong) that I need to use the
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
method in order to achieve this. Where I need help is I am not sure how to set the height of each cell at indexPath depending upon the 'identifier' that I gave each cell in the cellForRowAtIndexPath method.
What I'm looking for = Something like this (please excuse the SuedoCode)
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
if ([cell.identifier isEqual:#"Cell"] {
return 100;
}
else {
return 200;
}
}
ANSWER: I figured it out! (I marked the answer below as accepted because it pointed me in the right direction)
Because I am using a PFQueryTableViewController all I had to do this...
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
PFObject *object = [self.objects objectAtIndex:indexPath.row];
if ([object[#"orientation"] isEqual:#"left"] || [object[#"orientation"] isEqual:#"right"]) {
return 100;
}
else {
return 200;
}
}

First, some things to keep in mind. heightForRowAtindexPath is calledbefore CellForRowatIndexPath, and simply says, if object is at indexPath X, then return Y or Z.
The more correct approach might be to subclass the tableCell class, set a property in the .h file and then figure out the path... I'll give you a dirty way :)
Create an NSMutableArray property (don't forget to init it somewhere/somehow), and based on your dataSource, populate it with Height A or Height B (a float). Now, back in heightForRowAtIndexPath, you can say something to the effect of:
return (int)self.myMutableArray[indexPath.row];

Related

heightForRowAtIndexPath called before cellForRowAtIndexPath

I am trying to reduce duplicate code when laying out my tableview but running into lifecycle problems. Basically its that heightFroRowAtIndexPath is called before cellForRowAtIndexPath. Which is what should happen and I understand why.
But...
I have a cell that is laid out in a storyboard. It has an optional field. If the optional field is not in the data then I remove a label for that field. However I am removing that label in a custom cell implementation:
CustomCell (extends UITableViewCell)
- (void) configureCellForData: (Data *) data {
if (data.optional) {
self.optionalLabel.text = [data.optional];
} else {
[self.optionalLabel removeFromSuperview];
}
}
Then in cellForRowAtIndexPath:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:self.tableLayout[indexPath.section][indexPath.row]];
[cell configureCellForData:self.data];
return cell;
}
Which works great for setting up the cell. However the height is wrong if the optional field is removed, ie I need to adjust if the optional field was removed.
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:self.tableLayout[indexPath.section][indexPath.row]];
CustomCell *headerCell = (CustomCell *) cell;
if (self.data.optional == nil) {
return cell.bounds.size.height - headerCell.optionalLabel.bounds.size.height;
}
return cell.bounds.size.height;
}
}
It does not seem like much but I simplified my check to "data.optional == nil" and it is more complex than that and involves a DB call.
Is there a better way to set this up such that I don't have to make the check twice once when the height for cell is calculated and once when the cell is initialized?
If you wanted to only check once you could store an array of booleans that stores whether or not the data is there or not. So, make the check for each row, store the result into the array, before you make the check next time, check to see if the array has an value for that cell, if it does, use that value, if not, make the database call.
Make sure that you only store values in the array index associated with the indexPath, and if the array is shorter than the indexPath you're at, you know you need to make the call and add the value into the array.
Edit: As I think more about it, I would put the bool value on the cell itself, and then just call cell.isDataAvailable (or whatever you want the value to be) in order to avoid the second call when you go to set the cell up, as you would have already checked this in heightForRowAtIndexPath.

Obtaining UITableViewCell selection status within tableView:heightForRowAtIndexPath:

I want to change the height of a UITableViewCell when it's selected because I'm using different cellPrototypes for selected and non-selected cells.
The cells are in a UITableView which is embedded in an UIView, which is the TableView's delegate and datasource.
But when I try to check whether the cell at indexPath is selected, I am apparently producing an infinite recursion.
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
CGFloat cellHeight = 64;
if ([tableView cellForRowAtIndexPath:indexPath].selected) {
cellHeight = 128;
return cellHeight;
}
Could you help me finding a working solution, please?
What you'r doing is wrong, because you call cellForRowAtIndexPath which cause the tableView to call heightForRowAtIndexPath, so you have the infinite recursion.
The best option to achieve what you want is by having an object to save the index path of the selected cell to make it wider
1) first have a global variable call it NSIndexPath currentSelectedCellIndex
2) in cellDidSelectCellAtIndexPath change the variable and reload the cell as follows
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
currentSelectedCellIndex = indexPath;
[self.tableView reloadRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationNone];
}
3) finally in heightForRowAtIndexPath return the new height for the selected cell
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
if(indexPath.row == currentSelectedCellIndex.row) {
// for example 60
return 60;
}
return 44;
}
Try to reload the tableView on didSelectRowAtIndexPath method.

Update single section of multi-section UITableView

I have a UITableViewController created in storyboard. It has two sections. The first section's rows contain controls laid-out in storyboard. I want to update the rows in the second section using values in an array.
I'm fairly new to iOS development. I understand how to use a UITableViewDataSource to update a table based on the array, but not how to restrict the updates to a specific section. Can anyone outline how to do this?
EDIT This seemed like a simple problem, so I thought I code would just obscure the question. Maybe I was wrong. Heres what I have:
My numberOfRowsInSection function returns 1 in the section number is 0, because the first section (the one I designed in storyboard) has a single row, otherwise it returns the number of elements in the backing data array:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
if (section == 0)
return 1;
else
return [myData length];
}
My cellForRowAtIndexPath function creates a cell if the section number is 1. But I don't know what to do if the section number is zero. How do I avoid having to recreate the rows I laid-out in storyboard?
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
if(indexPath.section == 1)
{
cell.textLabel.text = [myData objectAtindex:indexPath.row];
}
else
{
// What to do here?
}
}
Well If you only have few static controls in the first section why won't you put these controls in a table header view instead? Thus you'll only have one section to worry about :)
In your method - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPathadd this
Create 2 differents UITableViewCells and reference them like this
if (indexPath.section == 1) {
NSString *CellIdentifier = #"DynamicCell";
VideoCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
//You are drawing your second section so you can use your array as values
cell.property1...
cell.property2...
cell.property3...
return cell;
}else{//If you have only 2 sections then else represent your first section
//You are drawing your first section
NSString *CellIdentifier = #"StaticCell";
VideoCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
return cell;
}
You can change the row value in the delegate method
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
To identify the section, just use:
indexPath.section
You can use reloadRowsAtIndexPaths: with an array of all the indexPaths that are in the wanted section, built with a loop and a NSMutableArray.
- (void)reloadSections:(NSIndexSet *)sections
withRowAnimation:(UITableViewRowAnimation)animation;
The parameter "section" is An index set identifying the sections to reload.

First cell always empty in table. Display only from the second cell - Objective c

I have a table view which display the contacts from array. I setup the table view delegates by follows.
-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [contactArray count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *simpleTableIdentifier = #"ContactCell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:simpleTableIdentifier];
}
cell.textLabel.text = [contactArray objectAtIndex:indexPath.row];
return cell;
}
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
return 60.0;
}
But the first cell in the table view always empty. It starts display only from second cell. I thought it may be header view. So I removed the header using the following delegate methods.
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section
{
return 0.0;
}
But still have the problem. I attached the screenshot about this issue.
Any help will be appreciated.
Your TableView is fine and it is working correctly, this is due to some other problem that is included in iOS 7, that automatically scroll insets. To solve this problem, go to your storyboard and select the viewcontroller in which your TableView is and select the ViewController and select the Properties of that ViewController, and uncheck this checkbox, which is read as Adjust ScrollView Insets. See this screen shot,
Your table is correct.Just your table was auto adjusted by the viewController.
You can write self.automaticallyAdjustsScrollViewInsets = NO;
Your Deduction is wrong your first cell isn't missing, but your tableview has started by 64 points down. So change your frame of your tableview or your tableview constraints accordingly.
Tip : Try setting a background colour when you have to debug things like this to clear your doubts.

tableView: cellForRowAtIndexPath: get called not only for visible cells?

I have a tableView with sections, which could be opened and closed. So, when I tap on a section to open it, it is getting filled up with cells and -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *) get called exactly as much times as I provided in -(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section.
Is that correct? Shouldn't it be just number of visible cells?
Because in my case I have bad situation: I have a lot of custom cells (50~100 cells) and calling -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *) for each cell slows down the opening of a section, cause each time reading from nib is performed and cell content is being populated with image.
I've check visibility of cell inside -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *) like this:
if ([[self.tableView indexPathsForVisibleRows] containsObject:indexPath])
NSLog(#"visible %#", indexPath);
and it shows that from out of 45 cells, only 6 or 7 are visible. Others are out of visible area. But creating cells still performed.
Here is the code:
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *CellIdentifier = #"IVCell";
IVCamera *camera = [server.cameras objectAtIndex:indexPath.row];
IVServerListViewCell *cell = (IVServerListViewCell*)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
[[NSBundle mainBundle] loadNibNamed:#"IVServerListCell" owner:self options:nil];
cell = (IVServerListViewCell*)_tableViewCell;
self.tableViewCell = nil;
}
[cell textLabel].text = camera.cameraName;
cell.preview = camera.preview;
cell.userData = camera;
cell.isEnabled = (server.isInactive)?NO:camera.isOnline;
return cell;
}
Is it still correct? Or am I missing something?
increase your
estimatedRowHeight of UITableview.
Well, I somehow dealt with my problem. Here are my ideas and thoughts how I came to the solution. Maybe it could be helpful to somebody.
I've instructed memory allocations and call stack using Instruments during opening section events. It showed me, that the majority of time is spent on loading cell from nib file.
Firstly, that I've done was reducing the size of nib file, i.e. minimizing the number of views used in custom tableview cell (now its only 2 views and 2 labels, instead of 6 views, 2 images and 2 labels before). It gave me some improve in cells loading. Apple documentation suggests to use as few as possible views and do not use transparency. So be attentive to these suggestions.
Secondly, as I discovered earlier, that not all cell are visible which are created by -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *), I decided to reduce somehow the number of loadings new cells from nib file. To achieve this, I've came to simple idea: return blank default cells for invisible rows, while load custom cells from nib for visible ones. Here is the piece of code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
if ([self index:indexPath isInvisibleInTableView:tableView])
return [self getBlankCellForTableView:tableView];
// the rest of the method is the same
...
}
-(BOOL)index:(NSIndexPath*)indexPath isInvisibleInTableView:(UITableView*)tableView
{
NSMutableArray *visibleIndexPaths = [self getExtendedVisibleIndexPathsForTableView:tableView];
return ![visibleIndexPaths containsObject:indexPath];
}
-(UITableViewCell*)getBlankCellForTableView:(UITableView*)tableView
{
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"IVBlankCell"];
if (!cell)
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:#"IVBlankCell"] autorelease];
return cell;
}
As you can see, I'm not using just -(NSArray*)indexPathsForVisibleRows method of tableview for detecting visible cells. Instead, I've wrote my own method -(NSMutableArray*)getExtendedVisibleIndexPathsForTableView:(UITableView*)tableView. It was necessary because for some reason, when using -(NSArray*)indexPathsForVisibleRows the cells that are next to the last one visible cell or the cells that are previous to the first one visible cell were created as blank cells and looked like empty cells while scrolling. To overcome this, in -(NSMutableArray*)getExtendedVisibleIndexPathsForTableView: (UITableView*)tableView i'm adding border cells to the visible array cells:
-(NSMutableArray*)getExtendedVisibleIndexPathsForTableView:(UITableView*)tableView{
NSArray *visibleIPs = [tableView indexPathsForVisibleRows];
if (!visibleIPs || ![visibleIPs count])
return [NSMutableArray array];
NSIndexPath *firstVisibleIP = [visibleIPs objectAtIndex:0];
NSIndexPath *lastVisibleIP = [visibleIPs objectAtIndex:[visibleIPs count]-1];
NSIndexPath *prevIndex = ([firstVisibleIP row])?[NSIndexPath indexPathForRow:[firstVisibleIP row]-1 inSection:[firstVisibleIP section]]:nil;
NSIndexPath *nextIndex = [NSIndexPath indexPathForRow:[lastVisibleIP row]+1 inSection:[lastVisibleIP section]];
NSMutableArray *exVisibleIndexPaths = [NSMutableArray arrayWithArray:[tableView indexPathsForVisibleRows]];
if (prevIndex)
[exVisibleIndexPaths addObject:prevIndex];
[exVisibleIndexPaths addObject:nextIndex];
return exVisibleIndexPaths;
}
Thereby, I've reduced the time of opening sections with large number of custom cells, which was proved by Instruments tracing and felt while experiencing the app.
Simply add estimated height for UITableViewCell
Problem In my case was: cellforRowAtIndexPath was getting called array.count number of times, whereas, displayed cells where less than array.count.
To resolve this issue, I have just replaced,
(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
with,
(CGFloat)tableView:(UITableView )tableView estimatedHeightForRowAtIndexPath:(nonnull NSIndexPath )indexPath;
check your tableview size.
may be that your tableview height is very large that it keep loading cells until your cell fills all tableview size..
This seems correct yes. the idea about optimizing the loading itself lies within how "dequeueReusableCellWithIdentifier" works.
if u are loading the image from a remote location this is where u would want to optimize the code. but not from the loading of cells as this looks correct here.
I used some similar technique but since indexPathsForVisibleRows is sorted you don't need to use containsObject. Instead you can just do:
//
// Checks if indexPath is visible in current scroll state, we are expanding bounds by 1
// because the cells that are next to the last one visible or the cells that are previous
// to the first one visible could look empty while scrolling.
//
- (BOOL)isIndexPathVisible:(NSIndexPath *)indexPath
{
NSInteger row = [indexPath row];
NSArray *visible = [self.tableView indexPathsForVisibleRows];
NSInteger count = [visible count];
NSInteger first = (count > 0) ? MAX([visible[0] row] - 1, 0): 0;
NSInteger last = (count > 1) ? [visible[1] row] + 1: first + 2;
return row >= first && row <= last;
}
By the way; this assumes that you are using only one section. It won't work for more than one section.
Adding an else solved my problem.
Where I reseted any changes that were made to the cell.
if (! self.cell) {
self.cell = [[LanguageCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
self.cell.accessoryType = UITableViewCellAccessoryNone;
}
else
{
self.cell.checkImage.image = NO;
}

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