HOWTO: Sort TableView per column using NSSortDescriptor when column names are unknown? - objective-c

Question

I'm loading a CSV file that I know nothing about except that the first row are column headers, which could be anything. The number of columns is unknown too. I tried to add a sortDescriptorPrototype to each column and when I do I get up/down arrows visible in the TableView.
for(NSTableColumn * col in self.tableView.tableColumns){
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey: col.title ascending: YES];
col.sortDescriptorPrototype = sortDescriptor;
}
Each time I click on the column sortDescriptorsDidChange is called:
- (void)tableView:(NSTableView *)tableView sortDescriptorsDidChange:(NSArray *)oldDescriptors
{
[_data sortUsingDescriptors: [tableView sortDescriptors]];
[tableView reloadData];
}
_data is a NSMutableArray where data is stored and first row are the header names. Each row is another NSArray Unfortunately I get this error:
2017-04-17 12:35:09.979142+0200 Table Tool[20954:2577488] [General] [<__NSCFString 0x610000474840> valueForUndefinedKey:]: this class is not key value coding-compliant for the key beds.
2017-04-17 12:35:09.982161+0200 Table Tool[20954:2577488] [General] (
0 CoreFoundation 0x00007fffb31a837b __exceptionPreprocess + 171
1 libobjc.A.dylib 0x00007fffc7f9c48d objc_exception_throw + 48
2 CoreFoundation 0x00007fffb31a82c9 -[NSException raise] + 9
3 Foundation 0x00007fffb4c83e5e -[NSObject(NSKeyValueCoding) valueForUndefinedKey:] + 226
4 Foundation 0x00007fffb4b55d9c -[NSObject(NSKeyValueCoding) valueForKey:] + 283
5 Foundation 0x00007fffb4b59aac -[NSArray(NSKeyValueCoding) valueForKey:] + 467
6 Foundation 0x00007fffb4b55b79 -[NSArray(NSKeyValueCoding) valueForKeyPath:] + 448
7 Foundation 0x00007fffb4b7cc9f _sortedObjectsUsingDescriptors + 371
8 Foundation 0x00007fffb4be94f7 -[NSMutableArray(NSKeyValueSorting) sortUsingDescriptors:] + 468
9 Table Tool 0x00000001000051d8 -[Document tableView:sortDescriptorsDidChange:] + 184
10 AppKit 0x00007fffb0f05425 -[NSTableView setSortDescriptors:] + 260
11 AppKit 0x00007fffb13c9fbc -[NSTableView _changeSortDescriptorsForClickOnColumn:] + 480
Obviously I have read a lot on the topic, but all examples assume that you know column names at design-time. I'm interested in a solution with NSSortDescriptor and sortUsingDescriptors in Obj-C or Swift, some explanation on sortDescriptorPrototype and why you need it in the first place, since sortDescriptor changes when I click on the column. Is there anything in KVC I can use for the sorting key, like "self" (there is ...valueForKeyPath:#"#sum.self"...)?
Some useful links:
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/TableView/SortingTableViews/SortingTableViews.html
https://www.raywenderlich.com/143828/macos-nstableview-tutorial

Answer 1

Here is a completely moronic way of solving it that partly works:
First I extract the column index with this method:
-(NSUInteger)getColumnIndexFromTableViewSortDescriptor {
for(NSUInteger i = 0; i < _maxColumnNumber; i++){
if(_tableView.tableColumns[i].title == _tableView.sortDescriptors[0].key){
return i;
}
}
assert(false && "Missing column name");
return 0;
}
Then I sort the array in-place with sortUsingComparator. Surely this has to be the "wrong". It's completely idiotic to use sortDescriptors if they are not used, other than to figuring out which column was clicked. I guess the click event could figure that out too?
-(void)tableView:(NSTableView *)tableView sortDescriptorsDidChange: (NSArray *)oldDescriptors
{
NSUInteger idx = self.getColumnIndexFromTableViewSortDescriptor;
if(tableView.sortDescriptors[0].ascending){
[_data sortUsingComparator: ^(id obj1, id obj2) {
return [[obj2 objectAtIndex:idx] compare:[obj1 objectAtIndex:idx]];
}];
} else {
[_data sortUsingComparator: ^(id obj1, id obj2) {
return [[obj1 objectAtIndex:idx] compare:[obj2 objectAtIndex:idx]];
}];
}
[tableView reloadData];
}
Now the CSV data I'm importing the data in the columns is not uniform, so it could be a NSNumber, followed by three NSDecimalNumber and a few NSString. Partly that's a problem with the data and/or the CSV parser I'm using (ripped from the web, but I will rewrite the sucker later).
So you could end up comparing NSDecimalNumber with NSString which will generate errors like:
unrecognized selector sent to instance
So I continued my stupidity with:
#interface NSDecimalNumber (CompareString)
-(NSComparisonResult)compare:(NSString *)string;
#end
#implementation NSDecimalNumber (CompareString)
-(NSComparisonResult)compare:(NSString *)string{
NSString *decimalString = self.stringValue;
return[decimalString compare:string options:NSCaseInsensitiveSearch];
}
Now if you compare two NSDecimalNumber the above will be called and the parameter "string" NSDecimalNumber, even though "string" declared NSString, resulting in "unrecognized selector sent to instance" once again.