Objective-C: How to refresh a UITableView? - ios

Question

I have some code that displays file name in my uitableview. however once deleting a file and refreshing i receive an error. Here is my code to display my file name, my delete button actions and the error:
Firstly when a button is pressed i run this code which works when adding a file to the table:
-(IBAction)refresh{
[[self mytable] reloadData];
}
Secondly I have this code to get and display the values the table is going to display. This works fine until the deletion and update occurs:
- (void)viewDidLoad
{
[super viewDidLoad];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
filePathsArray = [[[NSFileManager defaultManager] subpathsOfDirectoryAtPath:documentsDirectory error:nil]mutableCopy];
mytable.dataSource = self;
mytable.delegate = self;
}
-
-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
if(!filePathsArray)
{
return 0;
}
if ([filePathsArray count] > 0)
return [filePathsArray count];
else
return 0;
}
-
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
if (editingStyle == UITableViewCellEditingStyleDelete) {
//add code here for when you hit delete
NSString *currentFileName = filePathsArray[indexPath.row];
NSString *documentsDirectoryPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask,YES) objectAtIndex:0];
NSString *filePath = [documentsDirectoryPath stringByAppendingPathComponent:currentFileName];
fileURL = [NSURL fileURLWithPath:filePath];
NSLog(#"urlstring %#",fileURL);
NSFileManager *fileManager = [NSFileManager defaultManager];
[fileManager removeItemAtPath:filePath error:NULL];
NSLog(#"successfully deleted");
}
}
-
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"MainCell"];
if (cell == nil) {
cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:#"MainCell"];
}
NSLog(#"urlstring %#",[filePathsArray objectAtIndex:indexPath.row]);
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
filePathsArray = [[NSFileManager defaultManager] subpathsOfDirectoryAtPath:documentsDirectory error:nil];
cell.textLabel.text = [filePathsArray[indexPath.row] lastPathComponent];
filePathsArray = [[NSArray alloc] initWithArray: [[[NSFileManager defaultManager] subpathsOfDirectoryAtPath:documentsDirectory error:nil]mutableCopy]];
return cell;
}
-
-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView{
return 1;
}
The error i receive is this:
*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayI objectAtIndex:]: index 6 beyond bounds [0 .. 5]'
*** First throw call stack:
(0x2049012 0x1473e7e 0x1ffeb44 0x3c3a 0x69b8fb 0x69b9cf 0x6841bb 0x694b4b 0x6312dd 0x14876b0 0x2c84fc0 0x2c7933c 0x2c79150 0x2bf70bc 0x2bf8227 0x2bf88e2 0x2011afe 0x2011a3d 0x1fef7c2 0x1feef44 0x1feee1b 0x23dc7e3 0x23dc668 0x5e0ffc 0x2212 0x2145)
libc++abi.dylib: terminate called throwing an exception
(lldb)
I receive this error due to:
NSLog(#"urlstring %#",[filePathsArray objectAtIndex:indexPath.row]);
but once removed it says the problem is with the next line. Can anybody help?

Answer 1

Because of the way you're setting data in filePathsArray, your tableView is rendering one extra cell more than needed.
After you delete a file, update your filePathsArray.
What happens is that in your commitEditingStyle method you delete a file, but you do not update the filePathsArray object to remove the subpath for that file.
The only place where you update filePathsArray is in cellForRowAtIndexPath which is called after numberOfRowsInSection
So basically:
E.g. your filePathsArray contains subpaths for 6 files.
You delete a file in commitEditingStyle but you don't update filePathsArray (which still contains 6 subpaths).
You press the button to reloadData
numberOfRowsInSection is called to get the number of cells to be displayed on your UITableView... This returns [filePathsArray count] which is still 6.
cellForRowAtIndexPath is now called for every row.
Inside the above method, you call filePathsArray = [[NSFileManager defaultManager] subpathsOfDirectoryAtPath:documentsDirectory error:nil]; so now your filePathsArray has 5 objects because of the deleted file.
But guess what.... Your UITableView has already started rendering 6 rows for the old filePathsArray count.
Now when it renders cell number 6 (indexPath.row = 5), it calls cell.textLabel.text = [filePathsArray[indexPath.row] lastPathComponent]; and the last index of your array is now 4. This causes the crash.
Simply do filePathsArray = [[NSFileManager defaultManager] subpathsOfDirectoryAtPath:documentsDirectory error:nil]; in your commitEditingStyle and the error should stop.
Also, try not modifying your data source object in cellForRowAtIndexPath. Take the filePathsArray = [[NSFileManager defaultManager] subpathsOfDirectoryAtPath:documentsDirectory error:nil]; call out of there as your array is now being updated in commitEditingStyle.

Answer 2

In tableView:cellForRowAtIndexPath:, remove this code: filePathsArray = [[NSFileManager defaultManager] subpathsOfDirectoryAtPath:documentsDirectory error:nil];
In tableView:commitEditingStyle:,add this code:
[filePathsArray removeObjectAtIndex:indexPath.row];
This should maintain the integrity of the data you're using to populate the table view (so you don't change the number of items when the table doesn't know about it and you do change it when the table thinks you have).