Could not pass parameter to UITableViewCell - ios

Question

I have slightly different cells and for such purpose I need to pass parameter from my UIViewController to my subclass of UITableViewCell. But it does not work. The scenario is written as below:
MessagesViewController.m :
#import "MessagesViewController.h"
#import "MessageTableViewCell.h"
- (void)viewDidLoad
{
[super viewDidLoad];
[self.tableView registerClass:[MessageTableViewCell class] forCellReuseIdentifier:MessengerCellIdentifier];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
MessageTableViewCell *cell = (MessageTableViewCell *)[self.tableView dequeueReusableCellWithIdentifier:MessengerCellIdentifier];
if (cell == nil) {
cell = [[MessageTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:MessengerCellIdentifier customParam:YES];
}
return cell;
}
MessageTableViewCell.m :
- (instancetype)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier customParam:(BOOL)customParam
{
self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
if (self) {
// **** GET Custom Parameter (customParam) HERE ??? ****/
}
return self;
}
At this scenario customParam is my parameter. Everything seems as OK, but cell is not nil and so the procedure fails.

Answer 1

Option 1: Remove the dequeueReusableCellWithIdentifier line so that you create a new custom cell every time. Otherwise you are using a pre-existing cell that already has the previous customParameter set to whatever the last cell displayed was set to.
-Note to option 1 (added as explanation of why it is a very, VERY, VERY bad idea (#Duncan C). Since you are setting up your cells with a ReuseIdentifier in creating your cells iOS will hold on to them for you once they scroll offscreen so that you can reuse them when your code asks for it. But then your code never asks for reusable cells because it makes a completely new one each time the table asks for the next cell. This causes high load times (to create a new cell every time) and high memory use (since the OS is saving the cells for you to use later and not deallocating them immediately). The reusability was built for a reason, so don't use Option 1 unless you have very specific need to do so (and even then, you are probably wrong, don't do it).
Option 2: Change the custom parameter to a separate method call. Instead of in the initializer create a new method that clears the cell and rebuilds it the way your new custom parameter requires. Then you can re-use cells and modify their looks using the new setCustomParameter: method.
Edit: Code example of option 2, as simple as possible:
In table controller
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
MessageTableViewCell *cell = (MessageTableViewCell *)[self.tableView dequeueReusableCellWithIdentifier:MessengerCellIdentifier];
if (cell == nil) {
cell = [[MessageTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:MessengerCellIdentifier];
}
[cell setCustomParam:customParam];
return cell;
}
In your cell .m
-(void)setCustomParam:(ParamType)type
{
//Do whatever you would like right here to clear the previous
//cell's custom information and add the new custom information
//to this new cell.
}

Answer 2

Then you have to try some another method to add parameters in the MessageTableViewCell. The parameter is nil because the cell aren't nil everytime they are reusing the table view cell from the line
MessageTableViewCell *cell = (MessageTableViewCell *)[self.tableView dequeueReusableCellWithIdentifier:MessengerCellIdentifier];
You have to call another method like
MessageTableViewCell *cell = (MessageTableViewCell *)[self.tableView dequeueReusableCellWithIdentifier:MessengerCellIdentifier];
if (customParam)
{
// IF custom parameter is your labal
cell.yourCustomParameter.text = #"Add your content here"
}