table view data loading issue - objective-c

Question

I have a doubt in table view. I have placed a label & switch in table view cell. I set the switch value as NO by default. Now when table view is loaded in simulator the table view displays switch with NO value. Now I selected switch value as YES. But table view uses dequeue reusable cell method Property when table view is scrolled objects will reload every time now what will be the switch value will it be NO or YES?

Answer 1

It will be YES.
One more thing on scrolling tableview it not call reload method. Its just reusing already created tableview cells if you are using deque reusable cell method Property.

Answer 2

TableViewCells get destroyed and created where necessary when the table view gets scrolled.
When a cell gets destroyed as it goes out of the visible screen area, your switch control being a subview of the cell also gets destroyed.
So when you scroll back to one of your previously set switches, what you're actually seeing is another instance of a UITableViewCell with a switch view added to it, and so it looks like the switch value changed back to NO.
What you need is a third thing that remembers what the value of each switch should be in each row. If you're display a table of Core Data entity information, then perhaps you can define a property for your entity like "active". In that case, every time you change a switch value, you set your core data entity "active" property to the switch value e.g.:
-(UITableViewCell *)tableView:(UITableView)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
...
if(cell == nil)
{
// set switch control tag number (don't use 0)
}
// get switch control by tag number
// pseudocode
Engine *myEngine = [arrEngine objectAtIndex:indexPath.row];
mySwitchControl.active = myEngine.active;
...
}
// when you change switch value, remember to update your core data entity value
-(void)updateSwitchValue:(BOOL) newValue
{
// update value
}
Otherwise, you can simply use a NSMutableArray of bool values to identify which row each switch should be YES or NO:
// my header file (.h file)
#interface
{
NSMutableArray *arrSwitchValues;
}
// my implementation file (.m file)
-(UITableViewCell *)tableView:(UITableView)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
...
if(cell == nil)
{
// set switch control tag number (don't use 0)
}
// get switch control by tag number
// pseudocode
BOOL switchVal = [arrSwitchValues objectAtIndex:indexPath.row];
mySwitchControl.active = switchval;
...
}
// when you change switch value, remember to update your array
-(void)updateSwitchValue:(BOOL) newValue
{
// update value
}
Hope that helps.

Answer 3

to guarantee not have duplicated cells:
use this code in
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
as follows :
for(UIView *v in [cell subviews])
{
if([v isKindOfClass:[UILabel class]] ||[v isKindOfClass:[UISwitch class]])
[v removeFromSuperview];
}