I use Xamarin Studio to create a new custom table cell in a MonoTouch project (File -> New -> File... -> iOS -> iPhone Table View Cell). It creates MyViewCell subclass of UITableViewCell. The class already contains a static Create() method.
Then I use this class in table's GetCell method this way:
public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
{
var cell = tableView.DequeueReusableCell(MyViewCell.Key) as MyViewCell;
if (cell == null)
{
cell = MyViewCell.Create();
}
// my own code to update the cell content
cell.Update(someData);
return cell;
}
In Update method I use some subview transformations. The problem is that when the cell is first time created (Create method is called) the transformations are not applied.
But if I schedule the update to the next run loop iteration everything works fine:
NSTimer.CreateScheduledTimer(TimeSpan.Zero, () =>
{
cell.Update(someData);
});
What is the problem here? Can I solve the problem without using this hack?
the first time a cell has not been added in the table, when you called Update
for cell subview transformation override PrepareForReuse method or LayoutSubviews method on the cell class, depending on what you need.
Related
I've got a collection view with multiple cells created programically. I want to update a variable to a different value when the user taps a specific cell. So eg: Cell 1 is tapped -> var test = "cell1" , cell2 is tapped var test = "cell2". Usually I'd just create an IBAction by dragging from the storyboard but I'm not sure how to do it in this case.
I'm using Swift 3.1
To add interactivity to UITableViews, UICollectionViews, and other kinds of views which display collections of data, you can't use Storyboard actions, as the content is generated dynamically during runtime, and the Storyboard can only work for static content.
Instead, what you need to do is set your UICollectionView's delegate property to an object that implements the UICollectionViewDelegate protocol. One of the methods defined as part of the protocol is the collectionView(_:didSelectItemAt:) method. This method will get called whenever the user selects (taps) a collection view cell with the IndexPath to that cell as an argument. You can update your variable in that method. Just remember to deselect the cell after handling the tap by using the deselectItem(at:) method on your UICollectionView.
There are UICollectionView delegate that you need to implement. It goes like this
did select item at index path will give index path of the cell that was selected. Using indexpath or any other property of the data source array you are using, you can modify the variable value.
override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
if let cell = collectionView.cellForItemAtIndexPath(indexPath) {
//check your condition and modify the variable value depending on index path or any other property you are referring to.
}
}
Screenshot of weird behavior
The screenshot tells is quite well. I have a tableview with dynamic custom cells. I added a println for one of the contents of the cell to check, if the labels are set. I can see in the debug log, that each cell has its content. Still, on the device there are empty cells at random, which means, the row, where no content appears, is changing a lot. Even just scrolling up and down makes the second row disappear, but the third row is filled. Scrolling again turns this around again. If I close the app and start it again, every row is filled correctly.
Here is the code for the cell generation:
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
// Return a count picker cell
if countPickerTableRow == indexPath.row {
...
}
// Return a normal wish list entry cell
else {
let article = wishListEntries[indexPath.row]!
let cell = tableView.dequeueReusableCellWithIdentifier("ArticleCell", forIndexPath: indexPath) as! WOSArticleCell
// Correct the order in case a count picker cell was inserted
var row = indexPath.row
if countPickerTableRow != -1 && indexPath.row > countPickerTableRow {
row--
}
cell.setThePreviewImage(UIImage(data: article.thumbnail))
cell.setArticleName(article.name)
cell.setArticleDescription(article.text)
cell.setArticleNumber(article.number)
cell.setArticleCount(article.count as Int)
cell.setOrderInTable(row)
cell.setTableViewController(self)
cell.setNeedsDisplay()
cell.setInputAccessoryView(numberToolbar) // do it for every relevant textfield if there are more than one
println(String(indexPath.row) + " " + cell.nameLabel.text!)
return cell
}
}
In the custom cell class there is nothing special. Just a few outlets to the labels.
Here is a screen of the storyboard:
Storyboard
Can anyone please help me finding out what is going on here? I can't find the reason why the debug log can output the contents of a cell, but the device is not able to render them.
You should change the logic of your code. If the PickerCell comes up just call reloadData() and reload everything in the tableview. If the amount of rows you have is small this won’t be an issue and it’s not an expensive operation as you are not doing any heavy calculating during display.
If you need to update only a single cell because of changes you made in the PickerCell then you should be calling reloadRowsAtIndexPaths:withRowAnimation: with the indexPath of the cell to be updated.
Your issue is with your subclass WOSArticleCell. Have you implemented prepareForUse()? If you have, are you setting any properties to nil?
UITableViewCell Class Reference
Discussion
If a UITableViewCell object is reusable—that is, it has a reuse
identifier—this method is invoked just before the object is returned
from the UITableView method dequeueReusableCellWithIdentifier:. For
performance reasons, you should only reset attributes of the cell that
are not related to content, for example, alpha, editing, and selection
state. The table view's delegate in tableView:cellForRowAtIndexPath:
should always reset all content when reusing a cell. If the cell
object does not have an associated reuse identifier, this method is
not called. If you override this method, you must be sure to invoke
the superclass implementation.
Is it possible to create and use 'Custom' prototype table cells in xamarin ios (monotouch) using storyboard?
I could only find this by Stuart Lodge explaining a method using xib/nibs:
http://www.youtube.com/watch?feature=player_embedded&v=Vd1p2Gz8jfY
Let's answer this question! I was also looking for this one. :)
1) Open Storyboard where you have your ViewController with TableView:
Add prototype cell (if there is no cell added before):
Customize cell as you want (in my case there is custom UIImage and Label):
Remember to set height of the cell. To do it select your whole TableView and from the Properties window select "Layout" tab. On the top of the properties window you should see "row height" - put the appropriate value:
Now select prototype cell once again. In the Properties window type the name of the class (it will create code-behind class for it). In my case this is "FriendsCustomTableViewCell". After that provide "Identifier" for your cell. As you can see my is "FriendCell". Last thing to set is "Style" property set to custom. "Name" field should be empty. Once you click "enter" after typing "Class" code-behind file will be automatically created:
Now code behind for the cell should look like below:
public partial class FriendsCustomTableViewCell : UITableViewCell
{
public FriendsCustomTableViewCell (IntPtr handle) : base (handle)
{
}
public FriendsCustomTableViewCell(NSString cellId, string friendName, UIImage friendPhoto) : base (UITableViewCellStyle.Default, cellId)
{
FriendNameLabel.Text = friendName;
FriendPhotoImageView.Image = friendPhoto;
}
//This methods is to update cell data when reuse:
public void UpdateCellData(string friendName, UIImage friendPhoto)
{
FriendNameLabel.Text = friendName;
FriendPhotoImageView.Image = friendPhoto;
}
}
In UITableViewSource you have to declare cellIdentifier at the top of the class (in my case it is "FriendCell") and in "GetCell" method you have to cast cells and set data for them:
string cellIdentifier = "FriendCell";
public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
{
FriendsCustomTableViewCell cell = (FriendsCustomTableViewCell) tableView.DequeueReusableCell(cellIdentifier);
Friend friend = _friends[indexPath.Row];
//---- if there are no cells to reuse, create a new one
if (cell == null)
{ cell = new FriendsCustomTableViewCell(new NSString(cellIdentifier), friend.FriendName, new UIImage(NSData.FromArray(friend.FriendPhoto))); }
cell.UpdateCellData(friend.UserName, new UIImage(NSData.FromArray(friend.FriendPhoto)));
return cell;
}
That's it, now you can use your custom cells. I hope that it will help.
I am trying to add cells to a static table that I created using storyboard. I want to be able to add cell to one section of it dynamically from code, I implemented a custom UITableViewSource but it keeps overwriting my static cells. How should I implement GetCell() method so it will work with static cells too? Looks like in ObjectiveC it can be done by following:
return [super tableView:tableView numberOfRowsInSection:section]
But how to implement it in Xamarin iOS?
I was able to get it to work using this code:
public partial class StaticTableController : UITableViewController
{
public StaticTableController (IntPtr handle) : base (handle)
{
}
[Export("tableView:cellForRowAtIndexPath:")]
public UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
{
var selector = new Selector("tableView:cellForRowAtIndexPath:");
//WTF?
var cell = new UITableViewCell(Messaging.IntPtr_objc_msgSendSuper_IntPtr_IntPtr(SuperHandle, selector.Handle, tableView.Handle, indexPath.Handle));
if (indexPath.Row == 2)
{
cell.TextLabel.Text = "Dynamic thingy";
}
return cell;
}
}
Looks a bit weird, you might be better off using a dynamic table instead. One thing I tried that doesn't work is modifying the number of cells in a section -- this just seems to directly crash with the Obj-C version of an "index out of range" inside UITableView.
I'm figuring out the correct way to reuse cells in a UITableView and I would know if the mechanism I'm using is correct.
The scenario is the following.
I've a UITableView that displays a list of data obtained from a web service.
_listOfItems = e.Result as List<Item>;
where _listOfItems is an instance variable.
This list is passed to a class that extends UITableViewSource. Obviously this class override GetCell method to visualize data in this manner:
public override UITableViewCell GetCell (UITableView tableView, MonoTouch.Foundation.NSIndexPath indexPath)
{
UITableViewCell cell = tableView.DequeueReusableCell(_cID);
Item item = _listOfItems[indexPath.Row];
int id = item.Id;
if (cell == null)
{
cell = new UITableViewCell(UITableViewCellStyle.Value1, _cID);
cell.Tag = id;
_cellControllers.Add(id, cell);
}
else
{
bool vb = _cellControllers.TryGetValue(id, out cell);
if(vb)
{
cell = _cellControllers[id];
}
else
{
cell = new UITableViewCell(UITableViewCellStyle.Value1, _cID);
cell.Tag = id;
_cellControllers.Add(id, cell);
}
}
cell.TextLabel.Text = item.Title;
return cell;
}
where
_cID is an instance variable identifier for the cell
string _cID = "MyCellId";
_cellControllers is a dictionary to store cell and the relative id for an Item instance
Dictionary<int, UITableViewCell> _cellControllers;
I'm using the dictionary to store cells bacause when a row is tapped, I have to retrieve the id for the cell tapped (through cell.Tag value), do some other operation - i.e.retrieve other some data from the service - and then update that cell again with new values. In this case each cell has to be unique.
So, my question is:
Is this the right manner to reuse cell or is it possible to figured out another solution to reuse cell and guaranteeing each tap for a cell is unique?
I hope it's all clear :) Thank you in advance. Regards.
I think what you are doing here is a bit too much. Especially the part where you are holding extra references to cells in a Dictionary.
I would do it differently. The DequeueReusableCell method is there so that you can retrieve any existing cell, but not necessarily the values it contains. So something like this will suffice:
public override UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath)
{
int rowIndex = indexPath.Row;
Item item = _listOfItems[rowIndex];
UITableViewCell cell = tableView.DequeueReusableCell(_cID);
if (cell == null)
{
cell = new UITableViewCell(UITableViewCellStyle.Value1, _cID);
}
// Store what you want your cell to display always, not only when you are creating it.
cell.Tag = item.ID;
cell.TextLabel.Text = item.Title;
return cell;
}
Then, in the RowSelected method, change your data source:
public override void RowSelected (UITableView tableView, NSIndexPath indexPath){
// Do something here to change your data source _listOfItems[indexPath.Row] = new Item();
}
If I understand correctly what you want to do, this solution is better.
You will save yourself a lot of trouble if you use my MonoTouch.Dialog library that takes care of all of these details for you and does exactly what you want and more. It will let you focus on your app instead of focusing on the administrivia, and I believe will let you move faster, you can get it from:
http://github.com/migueldeicaza/MonoTouch.Dialog
The first problem with this code is that this hardcodes the cells to a single type. In general, you would have to first check the section/row and based on this information determine the kind of cell that you want.
Once you determine the kind of cell you want, then you use this information to call DequeueReusableCell with the token associated with this cell ID. This is different for example for a cell that contains an entry line vs a cell that contains an image. You need to dequeue the right kind of cell.
You do not need to make every cell unique, all the information that you need is in the section/row, so what you need is something that maps a section/row to your unique cell. A simple approach is that there is a single section, and the row is the index into your data array that you want to fetch more information from.
A small tutorial on best practices when creating these cells can be found here:
http://tirania.org/monomac/archive/2011/Jan-18.html
If you were using MonoTouch.Dialog, your whole code could be:
var elements = "foo, bar, baz";
var dvc = new DialogViewController ();
dvc.Root = new RootElement ("My results") {
from x in elements.Split (',')
select (Element) new StringElement (x);
};
dvc.Root.Add ("Final one");
current.PresentModalViewController (dvc, true);
The above creates a UITableView with 4 rows, one for "foo", "bar" and "baz" using Linq, and adds an extra node at the end just to show how to use the Add API.
There are also many assorted elements you can use, you are not limited to String elements.