I want to iterate all uitablewview cells and display the text of a uitextview contained in each cell.
My table can have many rows and to reach all you must scroll. I made an implementation, but it displays the text only for current visible cells in scroll, for the others gives me null.
for (int i = 0; i < [propertiesTableView numberOfRowsInSection:0]; i++) {
UITableViewCell* cell = [propertiesTableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:i inSection:0]];
UITextView* tx = (UITextView*)[cell viewWithTag:2];
NSString* temp = tx.text;
NSLog(#"%#", temp);
}
How to fix this?
This happens because only the visible cells are instantiated (remember the dequeueReusableCellWithIdentifier: function?). You should extract the needed information from the table data source.
Yes this behavior is expected, because of performance considerations the table view does not holds all cells initialized all the time. Your solution is just to update your data source - if it's an array for example, iterate though it and change the values accordingly - this is the power of MVC (fast UI, separate model)
Related
In my app I'm using ELCTextfieldCell. The idea is to use the data entered by the user for some calculations. But there is the problem. I have about 14 cells and, of course, they can't all fit on a screen. So when I click OK the app is checking if all fiels are filled in:
BOOL complete = YES;
for (int i = 0; i < [cellTextArray count] - [self.numberOfBools intValue]; i++) {
NSIndexPath *iPath = [NSIndexPath indexPathForRow:i inSection:0];
ELCTextfieldCell *theCell = (ELCTextfieldCell *)[self.tableView cellForRowAtIndexPath:iPath];
if (!theCell.rightTextField.text)
complete = NO;
}
This code works perfectly if all the cells are visible, but if some are out, then the complete becomes NO. The output of theCell in gdb is:
(gdb) po theCell
Can't print the description of a NIL object.
Can somebody push me in a right direction please? :)
All help will be appreciated, thank you.
EDIT
self.numberOfBools is just an NSNumber with total of bools in these rows. They are using UISwitches, not UITextField as the other cells, so I excluded them from the check.
Complete needs to be calculated on the data that is backing the cells rather than on the cells themselves. Let me explain.
The cell is a visual representation of your data and when it is not in view the run-time will release it and that is why it is nil.
However cellForRowAtIndexPath: creates the cell from data right? (or it is normal to do so) so when the user updates the cell.rightTextField you should update data.rightTextField and then complete should be looking something akin to ... and this is pseudocode not compilable
complete = YES;
for (Data* data in myDataSet) {
if (!data.rightTextField)
complete = NO;
}
So, in summary cells represent data and they are not guaranteed to persist. You yourself can ensure the data is persisted; therefore test for completeness on the data and not on the cells.
This is by design. Cells in UITableView are reusable, and they can be released when invisible to save resources. You have to store your data somewhere else than in cells.
I agree with Damo and anticyclope here. You should have updated the
theCell.rightTextField.text
into your datasource of your table in the first place.
Then you could make your calculation based on the datasource.
Let textFieldArray be the datasource of your table.
NSMutableArray *textFieldArray;
myTableView.dataSource = textFieldArray;
Then need to update the datasource when the textfield is updated.
Finally you can process the datasource.
So I've been trying to load cells from a UITableView and put those into an NSMutableArray to be iterated through later. I have a method called populateArrayWithCells which works fine until I put in more than 6 cells. For some reason the object returned is nil. My code is below, StocksAndAccounts is the UITableView and I have subclassed the UITableViewCells in section 1.
- (void) populateArrayWithCells
{
for (int i = 0; i < [StocksAndAccounts numberOfRowsInSection:1]; i++) {
if ([StocksAndAccounts cellForRowAtIndexPath:[NSIndexPath indexPathForRow:i inSection:1]] == nil) {
NSLog(#"object at index %i is nil", i);
}
[stocksCells addObject:[StocksAndAccounts cellForRowAtIndexPath:[NSIndexPath indexPathForRow:i inSection:1]]];
}
}
This function, when called through an IBAction, returns the cell successfuly until the index is 6, in which case it is nil and crashes because it's trying to add an object that is nil. Any help with this problem would be greatly appreciated.
I think you've misunderstood how UITableViews work. The cells in a tableview are only loaded when they need to be displayed, and they are recycled, so if you can only see six cells on screen at a time then the table will only ever contain six cells and it will just keep updating and reusing those same six as you scroll up and down.
Instead of storing data in your table cells, store it in an array of custom objects in your view controller and use those objects to populate the cells when the table requests them from your datasource methods.
That way if you ever need to use that data for something other than displaying in the table, you can re-create it from the original object instead of trying to copy it out of the table cell.
You are doing it backwards.
Your NSMutableArray (and preferably a sturdier model than that) should be holding what you want to display in your UITableView, not the other way around. Please review the Model-View-Controller design pattern.
This page
http://networkpx.blogspot.com/2009/07/multiple-row-selection-with-uitableview.html
mentions a way to implement table views that can allow multiple selections of rows.
At the time of this article, it seems that it was not a blessed way of doing this.
Now, apparently, Apple is allowing this kind of tableViews.
The article mentions this
NSArray* selectedRows = [tableView indexPathsForSelectedRows];
as a way of getting a list of all rows selected but this is not a legal functionality of the SDK.
The big question is: how do I get a list of all rows selected, so I can perform an action with them?
thanks
EDIT
To answer some questions... this is the code I am using to discover if a row is selected, but this is giving me zero entries.
NSMutableArray *selectedRows = [[NSMutableArray alloc] init];
for (int i=0; i<[list count]; i++) {
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:i inSection:0];
UITableViewCell *aCell = (UITableViewCell*) [myTable cellForRowAtIndexPath:indexPath];
if (aCell.accessoryType == UITableViewCellAccessoryCheckmark) {
[selectedRows addObject:indexPath];
}
}
// selectedRows has always 0 entries... all cells give me their type as UITableViewCellAccessoryNone even those with checkmark
Apple will reject your app for for iOS 4 and below.
We found the following non-public API/s in your app:
indexPathsForSelectedRows
Create a NSMutableArray.
Whenever a table cell is selected insert the current indexpath in the array. whenever he deselects the cell remove it from the array. Final array will have everything you selected.
MultipleCheck in Table – UITableView Example with Demo
http://sugartin.info/2011/08/19/multiplecheck-in-table-uitableview/
Are you looking to have the user select multiple rows at the same time? If not you could create an array that holds each row that is selected as the user selects them.
Also for the check mark you could just subclass UITableViewCell.
How to subClass UITableViewCell and use it to not clear UILabel background color on UITabeViewCell selected?
I have a table view which I'm using for some settings in my app. The tables cells are all default (no customisation at all), and simply contain some text for their label and a UISwitch for the accessory view.
My problem is that I need a reference to the switch so that I know when it has been switched on and off.
Currently I am setting the 'tag' property of the switch to be that of the cell's index within the table (grabbed from [indexPath row] in tableView:cellForRowAtIndexpath:).
This is fine when you only have one Section in your table, but I am now adding a new section. The problem is that they are both 0 based indexed so the switches in each section will end up reusing the tags - which isn't good.
Any suggestions on a better way to achieve this?
Thanks.
If you know roughly how many sections and rows you will have, like oh, say, not more than 1 million rows per section, just hash the section and row like this:
const int oneMillion = 1000000;
int tag = (section * oneMillion) + row;
slider.tag = tag;
Then, to figure out the section and row, reverse the logic:
int tag = slider.tag;
int row = tag % oneMillion;
int section = tag / oneMillion;
NSIndexPath *indexPath = [NSIndexPath indexPathForRow: row inSection: section];
Now get the slider that is in the cell in that section,row of the table
UITableViewCell *sliderCell = [tableView cellForRowAtIndexPath: indexPath];
UISlider *slider = [[sliderCell.contentView subviews] objectAtIndex: 0];
This assumes the slider is always the only view in the contents of the cell.
This method is a bit longer than some of the other suggestions above, but it keeps you from having to cache references off to the side.
For each cell, set a delegate link back to the table view controller, and also some kind of row reference ID - then wire the switch to a cell IBAction method, that calls back to the delegate with the reference ID for that cell.
What you can do is either have an Array of arrays or a dictionary, key it by the section number (or in case of the array they will be in order of the section numbers), now to retreive a switch all you do assuming you know the section and the row number
UISwitch *switch=[[switchArray objectAtIndex:section] objectAtIndex:row];
or if you have a dictionary
UISwitch *switch=[[switchDictionary objectForKey:section] objectAtIndex:row];
I have a tableView that needs to be updated after information has been inserted from another view. If I perform a
[self.tableView reloadData];
The very next time I insert more information in another view and try to reload the table, all the currently visible rows are duplicated.
In other words, when I start up the app I have:
tableView:
Row 1
Row 2
Then I submit some information that will also show up in the table and suddenly I have:
tableView
Row 1
Row 2
Row 3 <- info I just added
Row 1
Row 2
My numberOfRowsInSection implementation looks like this:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [ItemsController sharedItemsController].count;
}
My cellForRowAtIndexPath implementation looks like this:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
ItemsController* controller = [ItemsController sharedItemsController];
NSMutableArray* recentItems = controller.listOfRecentItems;
CustomCell *cell = nil;
NSUInteger row = [indexPath row];
if( row < recentItems.count )
{
Items* item = [recentItems objectAtIndex:row];
if( recentCellData == nil )
recentCellData = [[NSMutableDictionary alloc] initWithCapacity:[indexPath length]];
if( [recentCellData count] > 0 )
cell = [recentCellData objectForKey:[NSString stringWithFormat:#"%d", row]];
if (cell == nil) {
UIViewController * view1 = [[UIViewController alloc] initWithNibName:#"CustomCell" bundle:nil];
cell = (CustomCell*)[view1 view];
[recentCellData setObject:cell forKey:[NSString stringWithFormat:#"%d",row]];
}
// do some other stuff here
}
// Set up the cell
return cell;
}
What's the best way to update the table and avoid duplicating the currently visible rows.
Thank in advance for all the help!
The error isn't in how you're reloading the table, it's in how you're providing data to it. Set a breakpoint in the data source methods and the method that adds new rows to see where you're going wrong.
You'll only end up with five items if tableView:numberOfRowsinSection: returns 5. Thats the simple answer to your question, but I see other problems here. I'm wondering why you have this test: row < recentItems.count. Is that array the same thing as [ItemsController sharedItemsController].count? You really need to be using the same array for both methods.
(Also, it's not a syntax error, but you shouldn't use the property syntax for things that aren't declared as properties. You should write [recentItems count] instead.)
I'm also confused by the code you use to set up the cell. Cells are meant to be reusable. That is, you create one cell, then reconfigure it every time in your implementation of tableView:cellForRowAtIndexPath:. Your code creates a cell for each item in your list. This is very memory-inefficient, and will likely crash your program due to insufficient memory on the iPhone if you keep lots of cells in memory like this.
The recommended approach is to call dequeueReusableCellWithIdentifier:. If that returns nil, then you set up a cell using the initWithFrame:reuseIdentifier: initializer. The table view is very smart, and will only ask you to redraw the cell when it needs you to.
Your recentCellData dictionary looks really shaky to me, too. What if you insert an item after the item with key #"2"? All the items with key #"3" onward will need to be shifted one element to the right to work the way you expect. That's a ton of bookkeeping that seems rather unnecessary to me. If you really needed something like this -- and to be clear, I don't think you do -- why wouldn't you use an NSMutableArray, which is much easier to use?
I added a bit more info above.