From Swift to Objective C - updateCallDurationForVisibleCells - objective-c

Question

I'm trying to covert Speakrbox code in Objective-C.
I have already converted most of the code but I have a little problem with this one:
private func updateCallDurationForVisibleCells() {
/*
Modify all the visible cells directly, since -[UITableView reloadData] resets a lot
of things on the table view like selection & editing states
*/
let visibleCells = tableView.visibleCells as! [CallSummaryTableViewCell]
guard let indexPathsForVisibleRows = tableView.indexPathsForVisibleRows else { return }
for index in 0..<visibleCells.count {
let cell = visibleCells[index]
let indexPath = indexPathsForVisibleRows[index]
guard let call = call(at: indexPath) else { return }
cell.durationLabel?.text = durationLabelText(forCall: call)
}
}
I tried to convert it, and here is what I have:
-(void) updateCallDurationForVisibleCells :(id)sender {
/*
Modify all the visible cells directly, since -[UITableView reloadData] resets a lot
of things on the table view like selection & editing states
*/
_visibleCells = _tableview.visibleCells;
if(_indexPathsForVisibleRows == _tableview.indexPathsForVisibleRows) { return ; }
int index;
for (index=0; index<_visibleCells.count; index ++)
{
UICollectionViewCell *cell = _visibleCells[index];
NSIndexPath *indexPath = _indexPathsForVisibleRows[index];
UITableViewCell* call;
if((call = [self.tableView cellForRowAtIndexPath:indexPath]))
{ return ; }
}
}
Could any one please help me to convert this Swift code into Objective-C? The code doesn't compile for the reason that I didn't know how to convert this line of code:
cell.durationLabel?.text = durationLabelText(forCall: call)
Also, I don't know if I did it in the right way, especially the conversion of guard let.
you will find here Call and durationLabelText functions that I have used in pdateCallDurationForVisibleCells function:
private func call(at indexPath: IndexPath) -> SpeakerboxCall? {
return callManager?.calls[indexPath.row]
}//swift
private func durationLabelText(forCall call: SpeakerboxCall) -> String? {
return call.hasConnected ? callDurationFormatter.format(timeInterval: call.duration) : nil
}//Swift

Answer 1

Here's a fixed up version of your Objective-C code. Please note that when you see var or let in Swift, you are creating a local variable. Do not create a bunch a needless instance variables or properties in the Objective-C code when you should just use local variables.
- (void)updateCallDurationForVisibleCells {
/*
Modify all the visible cells directly, since -[UITableView reloadData] resets a lot
of things on the table view like selection & editing states
*/
NSArray *indexPathsForVisibleRows = self.tableView.indexPathsForVisibleRows;
if(!indexPathsForVisibleRows) { return ; }
NSArray *visibleCells = self.tableview.visibleCells;
for (NSInteger index = 0; index < _visibleCells.count; index++) {
CallSummaryTableViewCell *cell = visibleCells[index];
NSIndexPath *indexPath = indexPathsForVisibleRows[index];
SomeDataType *call = [self call:indexPath];
if (!call) { return; }
cell.durationLabel.text = [self durationLabelText:call];
}
}
There is some information missing which means this conversion may not be 100% correct.
You haven't shown the Objective-C signature of the call: method so I can't be sure how to call it properly and I don't know what data type to use for the call variable. Replace SomeDataType with the proper type.
You haven't shown the Objective-C signature of the durationLabelText: method so I can't be 100% sure about the proper way to call it.
If you post those details in your question I can be sure this answer is updated properly.

Answer 2

Edit: Thanks to users like #rmaddy, newbies like me get to learn how to write answers.Adding the final full code part.
Skip to the final part of the answer to get the working code.
In case you want to know where you went wrong, read the full answer.
There are multiple things that are possibly not right here, let me address what I know:
The guard statement is used for graceful exit. I'm no Java expert, but consider this to be like Exceptions in JAVA. The Obj-C code for your first guard would be:
if (nil == _tableview.indexPathsForVisibleRows){
return
}
This also means that there's no necessity for the _indexPathsForVisibleRows variable.
I'd recommend this article to understand guard better:
https://ericcerney.com/swift-guard-statement/
With respect to your second guard, please pay attention to detail.
call(at: indexPath) is not the same as cellForRowAtIndexPath.
call(at: indexPath) is a class function that returns a datatype, say CallType. cellForRowAtIndexPath is a UITableView function, that returns a cell.
The cell in the below line is more likely to be of type CallSummaryTableViewCell
UICollectionViewCell *cell = _visibleCells[index];
Regarding durationLabelText(), it seems to be a class function in the swift file whose declaration would be something like:
//Assume the type of "call" is CallType
private func durationLabelText(forCall call : CallType) -> String{
//your code here
}
The Objective-C equivalent would be:
-(NSString*) durationLabelTextForCall: (id<CallType>) call{
//your code here
}
The Objective-C call would be:
cell.durationLabel.text = [self durationLabelTextForCall: call]
So, the final code would be like this:
-(NSString*) durationLabelTextForCall: (id<CallType>) call{
//your code here
}
-(id<CallType>) callAtIndexPath:(NSIndexPath) indexPath{
//your code here
}
- (void)updateCallDurationForVisibleCells {
/*
Modify all the visible cells directly, since -[UITableView reloadData] resets a lot
of things on the table view like selection & editing states
*/
if (nil == _tableview.indexPathsForVisibleRows){
return
}
NSArray *visibleCells = self.tableview.visibleCells;
for (index=0; index<visibleCells.count; index ++)
{
CallSummaryTableViewCell *cell = visibleCells[index];
NSIndexPath *indexPath = _tableview.indexPathsForVisibleRows[index];
id<CallType> call = [self callAtIndexPath:indexPath];
if (nil == call){
return
}
cell.durationLabel.text = [self durationLabelTextForCall: call]
}
}