Develop Reference

ObjectListView editing doesn't work

I'm trying to create a simple listbox with ObjectListView (WinForm, C#). The goal is to have a single value (a double) and a check box.
I want to be able to edit the double value by Single Click, so here are the relevant lines of code from my MyWindow.Designer.cs file (i've left out the default values for efficiency):
this.olvDepths = new BrightIdeasSoftware.ObjectListView();
this.olvColumn1 = ((BrightIdeasSoftware.OLVColumn)(new BrightIdeasSoftware.OLVColumn()));
...
this.olvDepths.CellEditActivation = BrightIdeasSoftware.ObjectListView.CellEditActivateMode.SingleClick;
this.olvDepths.CheckBoxes = true;
this.olvDepths.CheckedAspectName = "IsDefault";
this.olvDepths.FullRowSelect = true;
//
// olvColumn1
//
this.olvColumn1.AspectName = "Depth";
this.olvColumn1.Text = "";
this.olvColumn1.IsEditable = true;
I then create a list of my class (ShieldingEntry) and use the olvDepths.SetObjects() with the list. My ShieldingEntry class looks like this:
public class ShieldingEntry
{
public double Depth { get; set; }
public bool IsDefault { get; set; }
}
However, when I click the field, it doesn't go into edit mode. I've also tried the DoubleClick, SingleClickAlways, and F2Only modes and they don't work either.
The Checkbox works fine.
************** I have additional information *********************
I've pulled and build the ObjectListView source, so I could step through it.
I put a breakpoint in the OLV StartCellEdit method and it gets called and appears to setup and select the control appropriately. It just never appears...
As I noted in the comments on the answer below, I've got this control on a tabbed dialog, and if I switch to another tab, then back, the control works fine.
What am I missing?

I've used ObjectListView before, and here is what I had to do:
Handle the CellEditStarting event. This event is raised when the cell goes into edit mode. Since OLV doesn't really have built-in editors, you have to make your own. Then handle the CellEditFinishing event to validate the data before putting it back into your model.
So first, handling the CellEditStarting event:
private void objlv_CellEditStarting(object sender, CellEditEventArgs e)
{
//e.Column.AspectName gives the model column name of the editing column
if (e.Column.AspectName == "DoubleValue")
{
NumericUpDown nud = new NumericUpDown();
nud.MinValue = 0.0;
nud.MaxValue = 1000.0;
nud.Value = (double)e.Value;
e.Control = nud;
}
}
This creates your editing control. If you want to make sure the size is right, you can set the size of the control (in this case a NumericUpDown) to the cell bounds using e.CellBounds from the event object.
This will show the editor when you click in the cell. Then you can handle the editor finished event to validate the data:
private void objlv_CellEditFinishing(object sender, CellEditEventArgs e)
{
if (e.Column.AspectName == "DoubleValue")
{
//Here you can verify data, if the data is wrong, call
if ((double)e.NewValue > 10000.0)
e.Cancel = true;
}
}
I don't think handling it is required, but its good practice to validate data from the user.
The editing control in the CellEditStarting event can be any control, even a user defined one. I've used a lot of user defined controls (like textboxes with browse buttons) in the cell editor.
[Edit]
I uploaded an example here dropbox link that seems to work. Might not be in the exact view as needed, but seems to do the job.

For anyone else with this problem. I had it specifically when trying to edit a 'null' value in a decimal? on the OLV on a tab page. Solution for me was to set UseCustomSelectionColors to 'False'. I didn't look elsewhere to see if it was reported as a bug. Seems like a bug.

Two-way bind a "virtual" list of strings to a column

I have a list of Strings.
Well, conceptually. They are stored somewhere else, but I want provide an object which acts like a list (and provides any necessary events on top of that), with properties that I could bind to.
I want to establish a two-way binding over this data, to display it as a modifiable column in a DataGrid. I have the following problems with that:
I can't make a two-way binding because the binding needs a path (i.e. I can't have it look like {Binding} or {Binding Path=.} in the column, must be {Binding Path=someField"} to be made modifiable if I got this right, which sounds reasonable).
I don't exactly know how the proxy collection object should look like, in terms of interfaces (would IEnumerable + INotifyCollectionChanged sufficient?)
Is there any solution which doesn't involve creating one proxy object per every String in the collection? Could you suggest an efficient design?
To keep the discussion on the rails, let's assume I want to bind to something like this:
class Source {
public String getRow(int n);
public void setRow(int n, String s);
public int getCount();
public void addRow(int position, String s);
public void removeRow(int position);
}
That's not exactly my case, but when I know how to bind to this, I think I'll be able to handle any situation like this.
I'm OK with having to provide an adapter object on top of that Source, with any necessary interfaces and events, but I don't want to have one adapter object per row of data.

While making an adapter for the Source is relatively clear, then, unfortunatelly, the core of the second problem ('not wrapping every string in a miniobject') is a clash built into the .Net and WPF..
The first thing is that the WPF does provide you with many ways of registering 'on data modified' callbacks, but provides no way of registering callbacks that would provide a value. I mean, the "set" phase is only extendable, not interceptable, and the "get" - nothing at all. WPF will simply keep and return whatever data it has once cached.
The second thing is that in .Net the string is ... immutable.
Now, if ever you provide a string directly as a pathless binding or as a datacontext to any control, you are screwed in a dead end. The problem is, that WPF actually passes only the actual value of the binding, without the information of "where it came from". The underlying control will be simply given the string instance, and will have no sane way of modifying it as the string cannot change itself. You will not be even notified about such attempt, just like with read-only properties. What's more - if you ever manage to intercept such a modification attempt, and if you produce a proper new string, the WPF will never ask you again for the new value. To update the UI, you'd have to mannually, literally, force the WPF to re-ask you by for example changing the original binding so it points elsewhere (to the new value) or set the datacontext (to the new instance). It is doable with some VisualTree scanning, as every 'changed' callback gives you the DependencyObjects (Controls!), so yo ucan scan upwards/downwards and tamper with their properties.. Remember that option - I'll refer to this in a minute.
So, everything boils down to the fact that to get a normal 2-way binding you do not have to have a Path, you "just" have to have a mutable underlying data object. If you have immutable one - then you have to use a binding to a mutable property that holds the immutable value..
Having said that, you simply have to wrap the strings some how if you want to modify them.
The other question is, how to do that. There's a plenty of ways to do it. Of course, you can simply wrap them like Joe and Davio suggested (note to Joe: INotify would be needed there also), or you can try to do some XAML tricks with attached properties and/or behaviours and/or converters to do that for you. This is completely doable, see for example my other post - I've shown there how to "inject a virtual property" that pulled the data completely from elsewhere (one binding+converter performed the wrapping on the fly, second binding extracted the values from the attached-wrapper). This way you could create a "Contents" property on the string, and that property could simply return the string itself, and it'd be completely 2-way bindable with no exceptions.
But.. it would NOT work 2-way-ish.
Somewhere at the root of your binding/behaviour/conveter chain, there will be an immutable string. Once your smart autowrapping binding chain fires with 'on modified' callback you will be notified with pair of old/new values. You will be able to remap the values to new and old strings. If you implemented everything perfectly, the WPF will simply use the new value. If you tripped somewhere, then you will have to push the new value artificially back to the UI (see the options I'd asked you to remember). So, it's ok. No wrapper, old value was visible, it was changeable, you've got new value, the UI displays new value. How about storage?
Somewhere in the meantime you've been given a old/new value pair. If you analyze them, you'll get old/new strings. But how do you update the old immutable string? Can't do. Even if autowrapping worked, even if UI worked, even if editing seemed to work, you are now standing with the real task: you onmodified callback was invoked and you have to actually update that immutable string piece.
First, you need your Source. Is it static? Phew. What a luck! So surely it is instanced. In the on-modified callback we got only a old+new string.. how to get the Source instance? Options:
scan the VisualTree and search for it in the datacontexts and use whatever was found..
add some more attached properties and binding to bind a virtual "Source" property to every string and read that property from the new value
Well doable, but smells, but no other options.
Wait, there's more: not only the old/new value and an instance of Source are needed! You also need the ROW INDEX. D'oh! how to get that from the bound data? Again, options:
scan the VisualTree and search for it (blaargh)...
add some more attached properties and bindings to bind a virtual "RowIndex" property to every (blaaergh)...
At this point of time, while I see that all of this seems implementable and actually might be working properly, I really think that wrapping each string in a small
public class LocalItem // + INotifyPropertyChanged
{
public int Index { get; }
public Source Source { get; }
public string Content
{
get { Source...}
set { Source... }
}
}
will simply be more readable, elegant and .. SHORTER to implement. And less error-prone, as more details will be explicit instead of some WPF's binding+attached magic..

I find your approach a little weird.
DataGrids are usually used to display Rows. Rows consist of data that belongs together.
You could for instance easily map a row to a certain class. This means that the columns in your datagrid represent properties in your class.
What you're trying to do is the opposite, you're trying to get a relation between the column values instead of the row values.
Wouldn't it be easier to have a collection of your class which you can then bound the column to?
For instance
class MyClass : INotifyPropertyChanged
{
// Remember to actually implement INotifyPropertyChanged
string Column;
}
If you would have an ObservableCollection of MyClass you could bind the DataGrid to this collection. Whenever the property which I called "Column" changes, you could update your special list.
You can do this by hooking up some events. With the implementation of INotifyPropertyChanged, your columns will be updated if you update the "Column"-value directly.

I have this bit of code I use to bind a list of custom object to a DataContextMenu. You can alter it to use a list of strings and bind it to what you need
class SampleCode
{
class Team
{
private string _TeamName = "";
private int _TeamProperty1 = 0;
ObservableCollection<Territory> _Territories = new ObservableCollection<Territory>();
public Team(string tName)
{
this.TeamName = tName;
}
public ObservableCollection<Territory> Territories
{
get { return _Territories; }
set { _Territories = value; }
}
public string TeamName
{
get { return _TeamName; }
set { _TeamName = value; }
}
public int TeamProperty1
{
get { return _TeamProperty1; }
set { _TeamProperty1 = value; }
}
}
class Territory
{
private string _TerritoryName = "";
Team _AssociatedTeam = null;
public Territory(string tName, Team team)
{
this.TerritoryName = tName;
this.AssociatedTeam = team;
}
public Team AssociatedTeam
{
get { return _AssociatedTeam; }
set { _AssociatedTeam = value; }
}
public string TerritoryName
{
get { return _TerritoryName; }
set { _TerritoryName = value; }
}
public void Method1()
{
//Do Some Work
}
}
class MyApplication
{
ObservableCollection<Team> _Teams = new ObservableCollection<Team>();
ContextMenu _TeritorySwitcher = new ContextMenu();
public MyApplication()
{
}
public void AddTeam()
{
_Teams.Add(new Team("1"));
_Teams.Add(new Team("2"));
_Teams.Add(new Team("3"));
_Teams.Add(new Team("4"));
foreach (Team t in _Teams)
{
t.Territories.Add(new Territory("1", t));
t.Territories.Add(new Territory("2", t));
t.Territories.Add(new Territory("3", t));
}
SetContextMenu();
}
private void SetContextMenu()
{
HierarchicalDataTemplate _hdtTerritories = new HierarchicalDataTemplate();
_hdtTerritories.DataType = typeof(Territory);
HierarchicalDataTemplate _hdtTeams = new HierarchicalDataTemplate();
_hdtTeams.DataType = typeof(Team);
FrameworkElementFactory _TeamFactory = new FrameworkElementFactory(typeof(TreeViewItem));
_TeamFactory.Name = "txtTeamInfo";
_TeamFactory.SetBinding(TreeViewItem.HeaderProperty, new Binding("TeamProperty1"));
FrameworkElementFactory _TerritoryFactory = new FrameworkElementFactory(typeof(TreeViewItem));
_TerritoryFactory.Name = "txtTerritoryInfo";
_TerritoryFactory.SetBinding(TreeViewItem.HeaderProperty, new Binding("TerritoryProperty1"));
_hdtTeams.ItemsSource = new Binding("Territories");
_hdtTeams.VisualTree = _TeamFactory;
_hdtTerritories.VisualTree = _TerritoryFactory;
_hdtTeams.ItemTemplate = _hdtTerritories;
_TeritorySwitcher.ItemTemplate = _hdtTeams;
_TeritorySwitcher.ItemsSource = this._Teams;
}
}
}

Lazy solution
Derive from ObservableCollection<string> and let that collection be populated from the Source. In the derived class, register to collection change events and update the source accordingly. Bind the DataGrid column to the observable collection.
This should be pretty straightforward to write, but has a big drawback of duplicating all data in the collection.
More efficient solution
Create an adapter (as you suggested) and implement IList<string> and INotifyCollectionChanged. Let the list operations fall through directly to the source. Bind the DataGrid column to the adapter.
This approach would require some tedious boilerplate, but it's a thin layer between the WPF control and your Source.

This really depends on how you're implementing the UI. Bea Stollnitz did an excellent post of virtualizing the ItemsSource for the WPF DataGrid at http://bea.stollnitz.com/blog/?p=344 . With work I used this to edit as well as display data.

The easiest way is by placing the string in a wrapper class.
public class Wrapper
{
public string Content{get;set;}
}
Then you use the string via the wrapper class. This was the list items remain the same but the content changes.
The problem is when you do this without that then an old string is being deleted and a new one is created and the collection is confused.

Start with an ObservableCollection<string>. Then set the bindable control's ItemsSource to the ObservableCollection.

Adding Items to ListView too slow in C#

I want to add item to listview control. This is a bit of code :
this.lView.ListViewItemSorter = null;
ListViewItem[] lvitems = new ListViewItem[ListMyObjects.Count];
int index = 0;
foreach (MyObject object in ListMyObjects)
{
ListViewItem item = new ListViewItem();
item.Text = object.Name;
lvitems[index++] = item;
}
this.lView.BeginUpdate();
this.lView.Items.AddRange(lvitems); // Slow in here with debugger
this.lView.EndUpdate();
I'm only add about 1000 item but it's very slowly. It's spend about 15secs to finish.
why does anyone know the reason ? Thank in advance.
Edit :
I have customized listview before.
public partial class MyListView: ListView
{
public MyListView()
{
InitializeComponent();
this.View = View.Details;
this.FullRowSelect = true;
this.DoubleBuffered = true;
}
private bool mCreating;
private bool mReadOnly;
protected override void OnHandleCreated(EventArgs e)
{
mCreating = true;
base.OnHandleCreated(e);
mCreating = false;
}
public bool ReadOnly
{
get { return mReadOnly; }
set { mReadOnly = value; }
}
protected override void OnItemCheck(ItemCheckEventArgs e)
{
if (!mCreating && mReadOnly) e.NewValue = e.CurrentValue;
base.OnItemCheck(e);
}
}
I do it because i don't want to hang when i use multiple threading. I don't know what does this influenced to it ?

You could make it much faster by enabling virtual mode.
However, that will take some work.

The preferred way of adding multiple items is to use the AddRange() method. However if you must add the items one by one you can use the BeginUpdate() and EndUpdate() methods around your loop. Following is from the MSDN
The preferred way to add multiple items to a ListView is to use the AddRange method of the ListView.ListViewItemCollection (accessed through the Items property of the ListView). This enables you to add an array of items to the list in a single operation. However, if you want to add items one at a time using the Add method of the ListView.ListViewItemCollection class, you can use the BeginUpdate method to prevent the control from repainting the ListView every time that an item is added.

Appologies for a more architectural solution, but if your domain objects are large this might cause the bottleneck (reading the comments it sounds like they may be slowing it down). Before you get to the presentation layer you could flatten them into some (very simple) domain transfer objects (DTOs): literally just a bag of getters-and-setters.
A tool like AutoMapper could potentially take a lot of the donkey work out there
That way your domain objects stay in the business logic domain (where they belong) and your presentation layer just gets the data in needs from the DTO.
Sorry for the non-code-based suggestion :) good luck!

Show only a part of an ItemsControl's source at first

I have an ItemsControl displaying a collection of files. Those files are sorted by most recent modification, and there's a lot of them.
So, I want to initially only show a small part (say, only 20 or so) of them, and display a button labelled "Show More" that would reveal everything when clicked.
I already have a solution, but it involves using a good old LINQ Take on my view model's source property. I was wondering if there was a cleaner way.
Thanks.

Why not have the object that you assign to the ItemsSource handle this logic - on first assignment, it would report a limited subset of the items. When Show More is clicked, the object is updated to show more (or all entries) and then notifies the framework that the property has changed (e.g. using the IPropertyNotifyChanged).
public class MyItemSource
{
private List<string> source = { ... };
public MyItemSource()
{
this.ShowThisMany = 20;
}
public int ShowThisMany
{
get;
set; // this should call\use the INotifyPropertyChanged interface
}
public IEnumerable<string> this[]
{
return this.source.Take(this.ShowThisMany);
}
}
...
MyItemsSource myItemsSource = new MyItemsSource();
ItemsControl.Source = myItemsSource;
...
void OnShowMoreClicked(...)
{
myItemsSource.ShowThisMany = 50;
}

In order to do this, you need to create some sort of 'view' on your data. There is nothing within the WPF framwork that will give you this functionality for free. In my opinion, a simple bit of Linq, Take(), is a clean and simple solution.

PropertyGrid alternatives

I love PropertyGrid, well, at least the concept behind it - use reflection and attributes to edit your objects without writing much UI code.
My excitement died out pretty quickly though, the default PropertyGrid shipping with WinForms flat-out sucks. Well, it's fine for editing simple objects and such, but that's as far as it goes.
It doesn't display appropriate UITypeEditors for dynamic properties which have type "Object".
As soon as your objects contain collections, you might be able to edit them with so called CollectionEditor. However, it won't fire PropertyValueChanged event. So once you need to add undo functionality, you're screwed.
And I still haven't found an elegant way to add validation for CollectionEditor.
It's also problematic to implement undo if you have multiple objects selected, because in that case PropertyValueChanged event args ChangedItem is null.
I soon found myself writing hacks to address those issues with less than agreeable results.
What would you do?
Is there an elegant solution to at least the first three issues?
Is there an alternative propertygrid? Preferably free & without PInvokes?

A lot of the PropertyGrid's elegance comes from its simplicity. Above all else, it's designed to play nice with Visual Studio, and i'd expect to see it used primarily in custom UITypeEditors and extensions, rather than in application code.
Presumably the objects you are attaching to the PropertyGrid are classes of your own design? I've found that, in order to make good use of the property grid, you have to heavily decorate your classes and members with attributes.
You may find some joy in writing your own subclasses of CollectionEditor (and other types of editors) and attaching them to class members using the [Editor] attribute - if you can attach this attribute to your dynamic properties, you can force the use of a particular editor.
The only way I can think of adding validation to CollectionEditor is to override the CreateCollectionForm() method, returning an instance of your own, custom subclass of CollectionEditor.CollectionForm. There's a chance you will be able to fire the change events from here.
Unfortunately all I can do is nod and agree with the assertion about implementing undo. You might have to resort to 'backing up' the affected objects via cloning or serialization in order to implement undo.
I've seen alternatives to the built-in property grid control, but they exist mainly to offer different visual styles.

If someone is interested - here is a workaround for the PropertyValueChanged problem that simulates a change by invoking the MemberwiseClone function of System.Object if the CollectionEditor's PropertyValueChanged had been fired ...
public class FixedCollectionEditor : CollectionEditor
{
bool modified;
public FixedCollectionEditor(Type type)
: base(type)
{ }
public override object EditValue(System.ComponentModel.ITypeDescriptorContext context, IServiceProvider provider, object value)
{
value = base.EditValue(context, provider, value);
if (value != null && modified)
{
value = value.GetType()
.GetMethod("MemberwiseClone", BindingFlags.Instance | BindingFlags.NonPublic)
.Invoke(value, new object[] { });
}
modified = false;
return value;
}
protected override CollectionForm CreateCollectionForm()
{
CollectionForm collectionForm = base.CreateCollectionForm();
foreach (Control table in collectionForm.Controls)
{
if (!(table is TableLayoutPanel)) { continue; }
foreach (Control c1 in table.Controls)
{
if (c1 is PropertyGrid)
{
PropertyGrid propertyGrid = (PropertyGrid)c1;
propertyGrid.PropertyValueChanged += new PropertyValueChangedEventHandler(GotModifiedHandler);
}
if (c1 is TableLayoutPanel)
{
foreach (Control c2 in c1.Controls)
{
if (!(c2 is Button)) { continue; }
Button button = (Button)c2;
if (button.Name == "addButton" || button.Name == "removeButton")
{
button.Click += new EventHandler(GotModifiedHandler);
if (button.ContextMenuStrip != null)
{
button.ContextMenuStrip.ItemClicked += new ToolStripItemClickedEventHandler(GotModifiedHandler);
}
}
}
}
}
}
return collectionForm;
}
void GotModifiedHandler(object sender, EventArgs e)
{
modified = true;
}
}

Visualhint sells a replacement for the property grid that may help. As I have never used it in a real project, I don't know how well it works.