Enum comboBox lists every item twice - winforms

I have a custom ComboBox in WinForms that is supposed to display an enumeration. Basically, I derived from ComboBox and in the constructor, I load the items from the enum.
The problem is that, even though at the end of the process it says the count of items is the same as the enum item count, the visual representation shows as if the same items were added twice. In other words, if my enum had values Value1 and Value2 the ComboBox says it has two values but when dropping down it shows Value1, Value2, Value1, Value2 as if I had added them twice.
public class EnumComboBox : ComboBox
{
public EnumComboBox() : base()
{
foreach (MyEnum p in Enum.GetValues(typeof(MyEnum)) {
base.Items.Add(p);
}
SelectedIndex = 0;
}
}
As you can see in the code, in the constructor the items are added ONCE but they are listed twice. What am I doing wrong here?

Rather than in the Constructor the manner to get it to behave properly was to leave the constructor empty and move the insertion code to the OnCreate method:
protected override void OnCreateControl()
{
if (!DesignMode) {
foreach (MyEnum p in Enum.GetValues(typeof(MyEnum))) {
Items.Add(p);
}
SelectedIndex = 0;
}
}

Related

Control Binding Times in XAML

I want To know if there is a way to Define how many times a Grid can bind to a list ?
for example , If I have a list of 20 elements , can I restrict the Binding To just the First Ten elements of the list .
the problem is that I use the same list for 2 different controls , I need the first control to bind to the entire all list , and the second to bind to the first 10 elements . so is there is anyway to do this from XAML ?
thanks :))
On your code-behind, or view-model, or wherever said list is, just set a property that exposes what you want:
public IEnumerable<something> MyTopElements
{
get { return myList.Take(10); }
}
and bind to that instead
in that case
public List<something> MyTopItems
{
get { return myItems.Take(10); }
}
public List<something> MyItems
{
get { return myItems; }
}

Setting the Text property of a DropDownList ComboBox to an invalid value doesn't raise exception?

I'm looking at ways to resolve an issue with a Winforms application, which uses a ComboBox control. Specifically, the ComboBox (Style=DropDownList) is bound to a datasource and, as the user navigates through some other data, the "Text" property of the ComboBox property is set - and the user can select some other value.
The trouble starts when the value I set the "Text" property to is not in the list of available items. It seems that nothing happens. Take the following simple example:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
myComboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
//myComboBox1.Items.AddRange(new[] { "One", "Two", "Three" });
List<KeyValuePair<Int32, String>> values = new List<KeyValuePair<Int32, String>>();
values.Add(new KeyValuePair<Int32, String>(1, "One"));
values.Add(new KeyValuePair<Int32, String>(2, "Two"));
values.Add(new KeyValuePair<Int32, String>(3, "Three"));
myComboBox1.DataSource = values;
myComboBox1.ValueMember = "Key";
myComboBox1.DisplayMember = "Value";
button1.Click += (s, e) => { myComboBox1.Text = "Four"; };
button2.Click += (s, e) => { myComboBox1.SelectedIndex -= 1; };
}
}
public class MyComboBox : System.Windows.Forms.ComboBox
{
public override string Text
{
get { return base.Text; }
set { MessageBox.Show(value); base.Text = value; }
}
}
This technique is used throughout a large application, so when it was noticed that (in the example above) setting the "Text" to "Four" does nothing, I thought that maybe I could trap this and throw an exception. In reality, the application is peppered with code like this:
if (myDataRow.IsBlahNull())
myComboBox1.Text = "";
else
myComboBox1.Text = myDataRow.Blah;
Now, while I appreciate that setting "SelectedIndex = -1" would be better for the "IsNull" case, the fact remains that myDataRow.Blah may not be a valid value. Also, the application is written (and live) so the fewer changes the better.
So, my immediate thought was "let's override the Text property setter and check that the value is in the list". That, it turns out, is nothing like as simple as it would seem. The problem being that the "Text" property is set to all kinds of things, in all kinds of scenarios. For example, it's set when the DataSource property is assigned, or when the SelectedIndex is set to -1. Also, it's set to the string representation of the selected item - so if you happen to have a ComboBox control that's bound to a List of KeyValue pairs, you get the "Text" property set to something like "[Key,Value]". If it's bound to a DataTable/DataView, you get the string representation of the DataRow, and that gets even harder to detect.
It's at this point I thought that there might be another way to achieve the desired result (which is to detect the setting of the Text property to some invalid value - which does nothing).
Any ideas ?
Upon reflection, is this a reasonable work-around ?
/// <summary>
/// Gets or sets the text associated with this control.
/// </summary>
public override string Text
{
get { return base.Text; }
set
{
base.Text = value;
if ((value != null) && (base.Text != value))
if (value == "")
this.SelectedIndex = -1;
else
throw new ArgumentException(String.Format("Cannot set Text property of {0} to \"{1}\".", this.Name, value));
}
}

Override two collection - pattern

I have Model like this
interface IStudent {
string Name;
List<Subjects> Marks;
int RollNumber;
}
class ViewModel {
ObservableCollection<IStudent> FromExcel;
ObservableCollection<IStudent> FromDB;
}
I need to bind the union of both collection on UI. Whats the best way. I was thinking of having another property ObservableCollection<IStudent> FromBoth; generated using LINQ Union method with comparer. My question is
Is it fine to have three collection to bind on UI? Note: I need to remove duplicates, giving priority to data from excel.
I need to pick some data from DB rather than excel in certain case.
For example: name="hungrymind" in fromExcel and name="hungrymind concepts" on fromDB collection. By default, grid on UI should show hungrymind (priority to excel), but if user uncheck column(aka property) from UI, then priority to data for that column becomes DB, i.e, UI should show "hungrymind concepts"
What should be approach to achieve this. My approach would be on user event, pick data from FromDB or FromExcel for each items in the collection and assign it to property in FromBoth collection. Since there are more than 100 columns, I had to use reflection, but wouldn't be slow down the performance? If I avoid reflection, then I have to write a method for each column. Any suggestion on pattern or approach ?
I solved the issue like this
interface IStudent {
string Name { get; set; }
List<Subjects> Marks { get; set; }
int RollNumber { get; set; }
}
class EntityViewModel: IStudent {
IStudent FromExcel;
IStudent FromDB;
public string Name {
get { return Choose("Name").Name; }
set { Choose("Name").Name = value; }
}
public string RollNumber{
get { return Choose("RollNumber").RollNumber; }
set { Choose("RollNumber").RollNumber = value; }
}
internal IStudent Choose(string propertyName){
if(IsOveridable(propertyName))
return this.FromExcel;
else
return this.FromDB
}
}
class ViewModel{
ObservableCollection<EntityViewModel> Entities;
}
In that case why don't you build a meta-model which would help you in organizing the data, like for instance
String objectName
String dataType
String defaultName
String displayName
String userSelectedName
boolean isUserOvverride
String viewType // (i.e. Text Input, Combo Box, Text Area, Radio Button, Multi Line List)
String viewElementTypeId // (i.e. for Combo Box,Radio Button this refers to user options available and for Text Input or Area it would be null)
Though the above approach decreases the performance but you can adopt to any number of types that might come in tomorrow.

How to achieve INotifyPropertyChanged functionality for the values in a bool[]?

I have a bool array of size 4 and I want to bind each cell to a different control.
This bool array represents 4 statuses (false = failure, true = success).
This bool array is a propery with a class:
class foo : INotifyPropertyChanged {
...
private bool[] _Statuses;
public bool[] Statuses
{
get {return Statuses;}
set {
Statuses = value;
OnPropertyChanged("Statuses");
}
}
In XAML there are 4 controls, each one bound to one cell of the array:
... Text="{Binding Path=Statuses[0]}" ...
... Text="{Binding Path=Statuses[1]}" ...
... Text="{Binding Path=Statuses[2]}" ...
... Text="{Binding Path=Statuses[3]}" ...
The problem is that the notify event is raised only when I change the array itself and isn't raised when I change one value within the array, i.e, next code line raises the event:
Statuses = new bool[4];
but next line does not raises the event:
Statuses [0] = true;
How can I raise the event each time one cell is changed?
You need to expose your statuses as an indexer, then raise a property change event that indicates that the indexer has changed.
private bool[] _Statuses;
public bool this[int index]
{
get { return _Statuses[index]; }
set
{
_Statuses[index] = value;
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(Binding.IndexerName));
}
}
See this blog post:
http://10rem.net/blog/2010/03/08/wpf---silverlight-quick-tip-inotifypropertychanged-for-indexer
It doesn't raise the event becuase Array itself doesn't implement INotifyPropertyChanged. You can either use a different container than the primitive array (anything that implements INotifyCollectionChanged liked ObservableCollection<T> should do) OR you have to call RaisePropertyChanged("Statuses") each time you update the Statuses array OR, as metioned in another answer, use one class that implement INotifyPropertyChanged that contains 4 properties.
You cannot do it while using an Array. Changing a value at any index on an Array does not raise change notification required by the UI.
Can you use a class with four properties that implements INotifyPropertyChanged interface instead?

WPF Create generic "Selector Tool" for multiple classes

the problem is pretty easy if you reduce it to one class. Given the following image, I want to create a simple two sided control, which puts items from one list into the other depending on a boolean value.
EDIT: You can of course click on items in both lists, and the item switches to the other list. Also, a callback is called, in case I need to update some DB stuff...
I created a nice picture to movivate you a little bit, because I am stuck...
The world is not so simple like the example: How would you solve this for various classes.
Imagine a class like "Car" with "IsFast". Or a class like "Fruits" with "ILikeIt". I do not want to reprogramm the WPF control each time, I need some way to bind... (oh, I think I just got an idea)... but still, is there any good practice how to allow generic classes (like T) as long as they implement certain properties.. Or a wrapper class?
I have no idea, how would you solve it. Simple binding with OnClick Functions seems not enough... Not sure... And, by the way, "write 3 controls" IS a suitable answer. If it is simpler, just tell me.
alt text http://img31.imageshack.us/img31/96/listexample.png
I think I understand what you are after, this should get you started.
I am assuming that your usercontrol has two listviews, one intended for the true items named "TrueList", the other for the false items named "FalseList".
Extend your usercontrol from ItemsCollection and bind the ItemsSource property of each listview to the ItemsSource of the parent usercontrol.
Add a TrueFilter and a FalseFilter property to your usercontrol:
Predicate<object> trueFilter;
public Predicate<object> TrueFilter
{
get
{
return trueFilter;
}
set
{
if (trueFilter!= null && this.TrueList.Items != null)
this.TrueList.Items.Filter -= trueFilter;
trueFilter = value;
if (trueFilter!= null && this.TrueList.Items != null)
this.TrueList.Items.Filter += trueFilter;
}
}
Predicate<object> falseFilter;
public Predicate<object> FalseFilter
{
get
{
return falseFilter;
}
set
{
if (falseFilter!= null && this.FalseList.Items != null)
this.FalseList.Items.Filter -= falseFilter;
filter = value;
if (falseFilter!= null && this.FalseList.Items != null)
this.FalseList.Items.Filter += falseFilter;
}
}
Then create an "IToggle" (or some other more meaningful name) interface:
public interface IToggle
{
Predicate<object> TrueFilter { get; }
Predicate<object> FalseFilter { get; }
}
Then, extend ObservableCollection for each of your custom classes, implementing the "IToggle" interface:
public class Cars : ObservableCollection<Car>, IToggle
{
Predicate<object> trueFilter;
public Predicate<object> TrueFilter
{
get
{
if (trueFilter == null)
trueFilter = new Predicate<object>(this.TrueFilterPredicate);
return trueFilter;
}
}
private bool TrueFilterPredicate(object value)
{
Car car = (Car)value;
return car.IsFast;
}
Predicate<object> falseFilter;
public Predicate<object> FalseFilter
{
get
{
if (falseFilter == null)
falseFilter = new Predicate<object>(this.FalseFilterPredicate);
return falseFilter;
}
}
private bool FalseFilterPredicate(object value)
{
Car car = (Car)value;
return !car.IsFast;
}
Next, override the ItemsSource property on your user control:
public new IEnumerable ItemsSource
{
get { return base.ItemsSource; }
set
{
if (value != null && !(value is IToggle))
throw new Exception("You may only bind this control to collections that implement IToggle.");
base.ItemsSource = value;
this.TrueFilter = base.ItemsSource == null ? null : (base.ItemsSource as IToggle).TrueFilter;
this.FalseFilter = base.ItemsSource == null ? null : (base.ItemsSource as IToggle).FalseFilter;
}
}
Finally, call TrueList.Items.Refresh() and FalseList.Items.Refresh() on your event callbacks to refresh the item views whenever you switch an item from true to false, and vice versa.
This solution still requires writing some implementation code for each custom class (the true and false filters), but it should keep the extra code to a minimum.
Alternatively, it would be a much simpler solution if you gave each of your custom classes a common interface, something like:
public interface Valid
{
bool IsValid { get; set; }
}
Then you could use a single set of filters (or style setters, or databinding with converters) to work against the "Valid" interface. Instead of "Car.IsFast" and "Fruit.ILikeIt" you would use "Car.IsValid" and "Fruit.IsValid".
How would I do it?
Create a control called PickList that subclasses ItemsControl and includes commands for picking a single item, picking all items, unpicking all items etcetera
Create a class called PickListItem that has an IsPicked property
Define the control template for PickList to include two ListBoxes and a bunch of buttons for picking one, all etcetera. The template would include a couple of CollectionViewSources to segregate those items that are picked (which would be on the right) from those that are not (which would be on the left)
You would then use this control just like any other ItemsControl, and reuse it for any data type you might have:
<PickList ItemsSource="{Binding People}">
<PickList.ItemContainerStyle>
<Style TargetType="{x:Type PickListItem}">
<Setter Property="IsPicked" Value="{Binding IsRich}"/>
</Style>
</PickList.ItemContainerStyle>
</PickList>
make a user control. add a SourceList dep. Property. Add a delegate property for your callback, add a delegate property for your "is in list" filter
use two ListBox controls ( a left and a right ), use CollectionViewSource to set the source of the two lists, using the filter delegate to determine membership.

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