I have a UITableView with a top navigation bar. The data for the UITableView comes from an array which contains more than 20 objects.
Everything is fine so far. However sometimes when i do repeated scrolling (fast), I find last row being repeated, sometimes gets cut into half, overwritten.
I am new to iPhone development and have no clue why this happens.
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
// Return the number of sections.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
// Return the number of rows in the section.
return [appDelegate.preList count];
}
// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
// Configure the cell...
Item *i=[appDelegate.preList objectAtIndex:indexPath.row];
cell.textLabel.text=i.iName;
cell.accessoryType=UITableViewCellAccessoryNone;
return cell;
}
I have attached a screenshot of my problem as well. Notice how the navigation bar and the last cell are.
Help would be greatly appreciated
This looks like you have added two identical table views to your view. If you place a break point on numberOfSections… and then inspect the tableView object, I bet you will find two different table views. Start by looking for places in your code where you [self.view addSubview:tableView] or something similar. Remember, if you are using IB to setup your table, you do not need to programmatically add it.
I think you are seeing this when scrolling fast because only then the tableView bounces leaving some content offset. You have probably added 2 tableViews back to back.
Related
Context
Building for iOS 7
Two UITableViews on a viewcontroller
Using constraints so tableview resize like I'd like for between 3.5inch and 4inch screen sizes.
What I've tried
Read UITableView documentation
Search stackoverflow
tried this code: [self.bottomTableView scrollToRowAtIndexPath:0 atScrollPosition:UITableViewScrollPositionTop animated:NO];
Result
The content in the bottom tableView loads in the middle of the tableview. I can scroll those cells upwards towards the top of the table view, but they "snap" back to the middle. How do I avoid this?
Update
This is how the tableview looks on load. The green background shows all the white space that left on the top half of the bottom table view.
This is the code:
#pragma mark - Table View Methods
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
if (tableView == self.topTableView) {
return [self.array count];
}
else{
return [self.array count];
}
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *simpleTableIdentifier = #"SimpleTableItem";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:simpleTableIdentifier];
}
if (tableView == self.topTableView) {
cell.textLabel.text = #"60";
return cell;
}
else{
cell.textLabel.text = #"60";
return cell;
}
}
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
}
Everything is fine with your code. It seems to be a bug with Xcode and iOS 7 unless I missed something in the WWDC documentation.
He applies the height of the navbar to the first element in the subviews array. It doesn't matter if the element is actually under the bar, he just blindly applies it. You can change the order in the storyboard, lets say you move the bottom tableview to the top, then the bottom view has the problem.
I see two options.
If you disable "Under Top Bars" on the ViewController everything is fine. Or you move the UILabel to the top. There is nothing he can adjust with the static label. Maybe Xcode 5.0.1 that was released with the Maverics GM will fix that. Still downloading that one. Will try as soon DL is done.
Here is an xcode project that I just did to ask this question:
http://www.mediafire.com/?z26ufsfhby62br9
Open the log and run it. You will find that it outputs display: x and create: x where x is a number 0 to 49 and corresponds to the cell of the same number. It should only output to 22 before any scrolling is performed as Apple are always boasting that their tableviews are loaded as needed.
It basically shows that tableView:willDisplayCell:forRowAtIndexPath: and tableView:cellForRowAtIndexPath: are fired for each cell pretty much as soon as the tableview appears, why is this?
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
NSLog(#"create: %i", indexPath.row);
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:CellIdentifier] autorelease];
}
// Configure the cell...
cell.textLabel.text = [NSString stringWithFormat:#"%i", indexPath.row];
return cell;
}
- (void) tableView:(UITableView *)tableView
willDisplayCell:(UITableViewCell *)cell
forRowAtIndexPath:(NSIndexPath *)indexPath {
NSLog(#"display: %i", indexPath.row);
}
Why are the above meothds called just after the tableView loads (and just before each cell appears)? Surely they should be called just before each cell appears only?
These are the default delegate methods.. This will be be called for each cell everytime.
You use willDisplayCell:forRowAtIndexPath: to configure things like font and text color. In the newer version of the iPhone, with certain table configurations, if you configure things like the label text color in the tableView:cellForRowAtIndexPath: method, your changes will be lost at some point before the cell is actually displayed. Here you can do things like change the label's color, adjust background highlighting, such things as these.
If your table view is reloading before it actually fully displays, that could cause the behavior you're seeing. Then the cells would get initialized, prepared for display, but then all of that would be lost (before even shown on screen) as the table is reloaded.
I have a UILabel in a custom UITableViewCell that gets resized when the device is rotated. The text in this label needs to be recalculated after the rotation because I am cutting it down to size and appending some text at the end.
E.g. the datamodel has: "This is a run-on sentence that needs to stop."
In portrait mode it becomes "This is a run-on sent... more"
In landscape mode it becomes "This is a run-on sentence that... more"
From (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation
I am able to access the visible UITableViewCells and update the descriptions.
The problem seems to be that there are UITableViewCells that are cached but I can't get to. When I scroll the UITableView after a rotation, one or two cells that are below the visible area after the rotation don't have the correct text in the label. So they haven't been rendered via (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath - but they weren't returned by [tableView visibleCells] (or via looping through all views returned via [tableView subViews]).
I've tried to access the "extra" cells via this method:
for (int index=max + 1; index < max + 3 && index < [cellTypes count]; index++) {
NSIndexPath *updatedPath = [NSIndexPath indexPathForRow:index inSection:0];
UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:updatedPath];
if (cell == nil) { continue; }
[self updateCellForRotate:cell forRow:index];
}
(where max is the biggest row returned from visibleCells) but cell is always nil.
Is there anyway to flush the cache of UITableViewCells so that they don't get re-used? Or to access them so I can update them?
Thanks!
Two things.
First. In your didRotateFromInterfaceOrientation method you can simply reload the visible rows like so:
- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation) fromInterfaceOrientation
{
[super didRotateFromInterfaceOrientation:fromInterfaceOrientation];
NSLog(#"didRotateFromInterfaceOrientation:%d",fromInterfaceOrientation);
[tableView reloadRowsAtIndexPaths:[tableView indexPathsForVisibleRows] withRowAnimation:UITableViewRowAnimationNone];
}
Then I would recommend you add either the interfaceOrientation number or simply the table width to the dequeue cell name that way the tableView knows that cells in one rotation are different from those in another. Like so:
- (UITableViewCell *)tableView:(UITableView *)tv cellForRowAtIndexPath:(NSIndexPath *)indexPath withType:(NSString *)s_type
{
UITableViewCell *cell = nil;
// add width of table to the name so that rotations will change the cell dequeue names
s_cell = [s_cell stringByAppendingString:[NSString stringWithFormat:#"%#%d",#"Width",(int)tv.bounds.size.width]];
NSLog(#"%#",s_cell);
cell = [tv dequeueReusableCellWithIdentifier:s_cell];
if( cell == nil ) {
cell = [[[UITableViewCell alloc];
initWithFrame:CGRectZero reuseIdentifier:s_cell] autorelease];
}
}
Firstly, to reload all of your table cells use [self.tableView reloadData]
Secondly, add the line of code that is responsible for the shrinking inside the (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath method.
Example:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
//Some identifier and recycling stuff
if (UIInterfaceOrientationIsPortrait(self.interfaceOrientation)) {
//Make labels smaller
}
else {
//Make them bigger
}
}
Or you can just call your updateCellForRotate:forRow: method when making them. But I'm not sure how that function works, so I can't be too specific.
When you create the cell in cellForRowAtIndexPath:, add it to an array. Then, loop through the array, updating the text as necessary.
Hope this helps,
jrtc27
EDIT:
You say they are custom cells - could you not update your text in your UITableViewCell subclass?
So, I was having (what I think was) a very similar problem recently, and none of the posted answers helped me, I'm sorry to say.
My issue was that I deliberately resized and repositioned the UITableView upon rotation, and I did that programatically. The table cells in portrait took up the width of the view, and in Landscape were made somewhat higher but less wide. I then repositioned the elements of the cell depending on the orientation we'd come to.
Upon application start, the first viewing of the table was fine. Then I rotated and found that I appeared to have two instances of some elements, and these appeared to be where the cells had been visible in the first table. Rotating back then corrupted the initial orientation table with elements from the previous table.
I tried all of the applicable answers above, until I looked closer at the cellForRowAtIndexPath code:
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
I understand cell re-use is a great idea and all, but I really didn't need to retain (as in preserve) any cells and wanted them all bright, spangly and new after each rotation.
EDIT: In my own app I'll have maybe 20-30 rows maximum, as I personally don't like hugely long tables. If there were going to be lots of rows returned for a particular query I'd have some filters available to the user to help them sort out which rows they wanted. If you're going to have loads of rows displayed, then dequeuing them may cause you a performance impact that you don't want.
All I did was comment out the if and the following bracket, and my table cells renewed exactly as I wanted them to:
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
//if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
//}
Apologies for the waffle, and the late answer to an old question.
Ben.
Waffles and cream, or syrup.
You can use this simple line on the shouldAutorotateToInterfaceOrientation method :
self.view.autoresizesSubviews = YES;
For me it works always successfully
I have a UITableView in that some cells are marked with UITableViewCellAccessoryCheckmark at the initialization of the view.
When the user selects another row, I have to check if the maximum number of selected rows was achieved before. To do that, I used the code bellow:
- (NSInteger)tableView:(UITableView *)tableView numberOfSelectedRowsInSection:(NSInteger)section{
NSInteger numberOfRows = [self tableView:tableView numberOfRowsInSection:section];
NSInteger numberOfSelectedRows = 0;
for (int i = 0; i < numberOfRows; i++) {
UITableViewCell *otherCell = [tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:i inSection:section]];
if (otherCell.accessoryType == UITableViewCellAccessoryCheckmark) {
numberOfSelectedRows++;
}
}
return numberOfSelectedRows;
}
If my number of rows is, as example, 20, the variable numberOfRows is setted correctly with 20. Lets say that 13 rows already are marked with UITableViewCellAccessoryCheckmark. So, numberOfSelectedRows should be 13 after the loop, but only the marked and VISIBLE cells are considered. So, if I have 9 cells showed and 7 are marked, the numberOfSelectedRows returns 7 instead of 13 (but the for iterate 20 times, as expected).
Is this a correct behavior of UITableView or it is a bug of iPhone simulator?
Thanks in advance.
Yes, it works as designed. You should never store model data in your views. UITableView knows nothing about the data, it only displays cells (and throws them aways as soon as they scroll off the screen). You need to store the checkmark state of each cell in a model object (e.g. an array) that you then access from your view controller.
This is correct behavior.
The UITableView is not a list. The system caches cell that are off screen to save memory and CPU and they can not be iterated over in a manner that makes sense.
Ok, you should keep track of the model/data and the tableView will keep track of displaying it. I have had some problems with this until I accepted that uitableView is not a list:)
So, have an array of objects that each corresponds to the data in the a cell. When building the individual cells like this:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *CellIdentifier = #"categoryCell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];
}
Item *item = [self.itemList objectAtIndex:indexPath.row];
[cell.textLabel setText:[item itemBrand]]; //notice that here we set the cell values
return cell;
}
The when a user clicks you change you model like this:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
NSLog(#"IndexPat.row%i", indexPath.row);
Item item = (Item*) [self.itemList objectAtIndex:indexPath.row];
//change the state of item
}
This way the tableView will update to resemble the model/data, you just managed the model.
I need help in using checkbox cell. I currently added the object to tableview. It looks ok until i tried building and running the program where I cannot check the checkbox. I am currently using a tableview which displays items runtime with a checkbox for each item so i can have multiple selections.
I am new to xcode and I have been stuck for a week with this problem. i tried google but still no luck.
Any snippets, answers, or explanations is very much appreciated.
First we need to edit this method: - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath. Assuming you generated a Navigation-based application, this method should already be there, only commented out. I don't know the exact details of your implementation, but you somehow have to keep track of the checkbox state for each cell in the tableView. For example, if you had a BOOL array, the following code would work:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
if (checkboxArray[indexPath.row])
checkboxArray[indexPath.row] = NO;
else
checkboxArray[indexPath.row] = YES;
[self.tableView reloadData];
}
Now that we know what cells need to have a checkmark next to them, the next step is to modify how the cell is displayed. - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath handles the drawing of each cell. Building off the previous example, this is how you would display the checkbox:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
if (checkboxArray[indexPath.row]) {
cell.accessoryType = UITableViewCellAccessoryCheckmark;
}
else
cell.accessoryType = UITableViewCellAccessoryNone;
// Configure the cell.
return cell;
}
If we don't call reloadData, the checkmark will not show up until it goes off-screen and reappears. You need to explicitly set the accessoryType each time because of the way cells are reused. If you set the style only when a cell is checked, other cells that may not necessarily be checked will have a checkmark when you go to scroll. Hopefully this gives you a general idea on how to use checkmarks.