I am having trouble attempting to perform a seemingly simple series databind on a livecharts piechart. The error I"m seeing in output is -
An unhandled exception of type 'System.NullReferenceException'
occurred in LiveCharts.dll Object reference not set to an instance of
an object.
Here is my binding -
<lvc:PieChart LegendLocation="None" Series="{Binding TodayValues}"
DataTooltip="{x:Null}">
</lvc:PieChart>
And here is my ViewModel property -
private SeriesCollection _todayValues;
public SeriesCollection TodayValues
{
get { return _todayValues; }
set { SetNotifyingProperty(() => TodayValues, ref _todayValues, value); }
}
private void LoadInventoryPieCharts()
{
_todayValues = new SeriesCollection
{
new PieSeries
{
Values = new ChartValues<double>{ 21 }
},
new PieSeries
{
Values = new ChartValues<double>{ 4 }
}
};
}
SetNotifyingProperty is just an iplementation of INotifyPropertyChanged and the LoadInventoryPieCharts gets called when the VM is loaded.
Any thoughts on what is missing that is causing a nullreferenceexceptio?
Related
I am using Xceed's wpf property grid control to show some of my configuration properties. I am doing via { SelectedObject="{Binding Entity.Configuration} } where Configuration object contains list of properties and this object is created at runtime using xml file.
I need to do validation on these properties (e.g. max/min values). However I didn't find any way of doing validation. Can anyone let me know if there is any?
Add the following to your class:
using System.ComponentModel.DataAnnotations;
public class YourClass : DataErrorInfoImpl
{
[Range(0, 100 , ErrorMessage = "The number must be from [0,100].")]
Double SomeNumberToValidate {get;set;}
}
public class DataErrorInfoImpl : IDataErrorInfo
{
string IDataErrorInfo.Error { get { return string.Empty; } }
string IDataErrorInfo.this[string columnName]
{
get
{
var pi = GetType().GetProperty(columnName);
var value = pi.GetValue(this, null);
var context = new ValidationContext(this, null, null) { MemberName = columnName };
var validationResults = new List<ValidationResult>();
if (!Validator.TryValidateProperty(value, context, validationResults))
{
var sb = new StringBuilder();
foreach (var vr in validationResults)
{
sb.AppendLine(vr.ErrorMessage);
}
return sb.ToString().Trim();
}
return null;
}
}
}
Disclosure: I pulled some of this code out of propertytools property grid. It works with both Xceed and PropertyTools library.
in My OpenViewModel i collect data:
private ObservableCollection<KeyValue> availableData;
public ObservableCollection<KeyValue> AvailableDatas
{
get { return availableData; }
set
{
if (value != availableData)
{
availableData= value;
NotifyOfPropertyChange("AvailableDatas");
}
}
}
method for collecting data:
public ObservableCollection<KeyValue> CollectData()
{
ConnectorClient client = null;
try
{
client = webservice.GetClient();
AvailableDatas = client.GetDatas();
client.Close();
}
catch (Exception ex)
{
webservice.HandleException(ex, client);
}
return AvailableDatas;
}
How to call the method CollectData in wpf and fill my COmboBox?
thx
You might simply call the method the first time the AvailableDatas property is accessed (e.g. from a binding in XAML):
private ObservableCollection<KeyValue> availableData;
public ObservableCollection<KeyValue> AvailableDatas
{
get
{
if (availableData == null)
{
availableData = CollectData();
}
return availableData;
}
set
{
if (value != availableData)
{
availableData = value;
NotifyOfPropertyChange("AvailableDatas");
}
}
}
Then you should change the CollectData method in a way that is does not also set the property:
public ObservableCollection<KeyValue> CollectData()
{
ConnectorClient client = null;
ObservableCollection<KeyValue> data = null;
try
{
client = webservice.GetClient();
data = client.GetDatas();
client.Close();
}
catch (Exception ex)
{
webservice.HandleException(ex, client);
}
return data;
}
You could override the OnActivated() event assuming you are using an IScreen implementation and load data in there, or just do it in the constructor or a custom Initialise method if you want to roll your own (or in the property accessor as someone has already said).
You can also use coroutines if you want some visual context for the user and a better tie in with CM actions
There is a nice simple implementation of a Loader class here which helps provide visual context to the user:
https://caliburnmicro.codeplex.com/wikipage?title=IResult%20and%20Coroutines&referringTitle=Documentation
This searches the visual tree for a BusyIndicator control and activates it whilst the content is loading e.g. ...
public class SomeViewModel : Screen
{
protected override void OnActivate()
{
RefreshData();
}
public void RefreshData()
{
Coroutine.BeginExecute(LoadData(), new ActionExecutionContext() { Target = this });
}
public IEnumerable<IResult> LoadData()
{
yield return Loader.Show("Loading Data...");
yield return new LoadSomeDataRoutine(client.GetDatas);
yield return Loader.Hide();
}
}
The reason to have a RefreshData method is that this also allows you to bind CM actions and allows the coroutine can grab more contextual information.
Obviously you have less need to worry about the async->sync benefits this gives in Silverlight because you are using WPF (but it still applies to async web service calls), however it still has many benefits and it also helps you to write reusable routines which become part of your application framework (e.g. some level of error handling/logging encapsulated in the IResult implementation etc)
You also mentioned filling the combobox... all you would need to do in CM is place a combobox on your control, and set it's Name property to the name of the property on your VM:
public class SomeViewModel : Screen
{
public ObservableCollection<MyObject> MyProperty { //blah blah... }
}
<UserControl .... blah>
<ComboBox x:Name="MyProperty" />
</UserControl>
This will fill the combobox with the items. You will still need to set the binding for SelectedItem/SelectedValue
I assume you know this already though - if not CM has some decent documentation:
https://caliburnmicro.codeplex.com/wikipage?title=Basic%20Configuration%2c%20Actions%20and%20Conventions&referringTitle=Documentation
im exploring WPF world, i find a great example on the web about how to use binding on xml
http://www.codeproject.com/Articles/37854/How-to-Perform-WPF-Data-Binding-Using-LINQ-to-XML
Now im trying to extends this example: i want to create a "class in the middle" between the XElement and the UI and bind all togheder in a chain so, if i have a modification into the xml, then i have the property in the middle class updated then the UI updated too.
Here some code:
This is the class that wrap the XElement
public class XElementDataProvider : ObjectDataProvider
{
public XElementDataProvider()
{
ObjectInstance = XElement.Load(#"C:\MyFile.xml");
}
private static XElementDataProvider instance;
public static XElementDataProvider Instance
{
get
{
if (instance == null)
{
instance = new XElementDataProvider();
}
return instance;
}
}
}
This is the MiddleClass
public class MiddleClass : DependencyObject
{
XElementDataProvider xElementDataProvider;
XElement myxml;
public MiddleClass()
{
//here i get my dataprovider
xElementDataProvider = XElementDataProvider.Instance;
myxml = xElementDataProvider.Data as XElement;
//i bind my internal collection to the Elements...
Binding binding = new Binding("Elements[book]")
{
Source = myxml,
Mode = BindingMode.Default//here i cant use TwoWay, give me //back an exeption
};
BindingOperations.SetBinding(this, XBookListProperty, binding);
//just to have confirmation of the adding
myxml.Changed += new EventHandler<XObjectChangeEventArgs (myxml_Changed);
}
void myxml_Changed(object sender, XObjectChangeEventArgs e)
{
}
//i use a DependencyProperty to have also a change callback
public static readonly DependencyProperty XBookListProperty =
DependencyProperty.Register("XBookList", typeof(IEnumerable),
typeof(MiddleClass),
new PropertyMetadata(XBookPropertyChanged)
);
//here i have a notification only at start but no when i add a new book
private static void XBookPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MiddleClass middleClass = d as MiddleClass;
middleClass.XBookPropertyChanged((IEnumerable)e.OldValue, (IEnumerable)e.NewValue);
}
private void XBookPropertyChanged(IEnumerable old, IEnumerable newValue)
{
}
//this is the propery i finally want to expose to the UI but im not able //to keep updated
public List<Book> bookList;
public List<Book> BookList
{
get
{
return bookList;
}
set
{
bookList = value;
}
}
//this is my internal list binded to the xml
private IEnumerable XBookList
{
get
{
return (IEnumerable)GetValue(XBookListProperty);
}
set
{
SetValue(XBookListProperty, value);
}
}
//here i try to add a book addind direcly to the xml//i expect a //notification of propery changed...but nothing
public bool AddBook(string name)
{
XElement newWorkSheet = new XElement("Book",
new XAttribute("Name", name)
);
myxml.Add(newWorkSheet);
return true;
}
Book is a class thar repersents a book, let say it has only a name propery for now.
The UI class misses but it should bind on public List<Book> BookList and show books names to the user in a ListBox
Enyone knows why i dont recive any notification...or what i have to do to keep the public List<Book> BookList synchronized with private IEnumerable<XBookList>?
OK, after many attempts, the only solution I found is this one:
to have notifications when something changes in the IEnumerable<XBookList> you need to clear it ad rebind after you modify it.
In this way you have a first, not used notification, about the clear and then another notification about the new set.
Then in the handler you can synchronize the new list with the old one.
public bool AddBook(string name)
{
XElement newWorkSheet = new XElement("Book",
new XAttribute("Name", name)
);
myxml.Add(newWorkSheet);
ClearValue(XBookListProperty);
Binding binding = new Binding("Elements[book]")
{
Source = myxml,
Mode = BindingMode.Default
};
BindingOperations.SetBinding(this, XBookListProperty, binding);
return true;
}
I'm currently struggling with one of the bindings I'm trying to add to my WPF project.
In the app I have a model with a bool property that cannot be used for databinding. Behind that property is a .NET remoting object that does some validation and writes the new value into the DB.
The requirement ist that the property should be displayed as checkbox, and as the user changes the value the new value should be immediatly provided to the .NET remoting object.
My approach so far:
I've created in my ViewModel with a DependencyProperty that is bound to my checkbox.
In the propertychanged handler of the DP, I'm writting the value to the property of the remoting object.
The problems I have with this approach:
if the validation within the .net remoting object raises an exception, this exception is swallowed. In addition the checkbox state and what's in the DB is not in sync. I tried to reset the value of the DP in case of an exception, but the checkbox doesn't reflect that.
What makes the situation even worse is the fact, that this WPF controls is integrated into an existing WinForms app.
So I would like to have the same behavior for these exceptions as I have implemented in my Application.ThreadException handler.
any ideas how to approach this?
The problem is that I heard only solutions for .NET 4.0 so far, but I'm working with 3.5SP1.
tia
Martin
Short demo code:
class TestVM : DependencyObject
{
private Model _m;
public TestVM()
{
_m = new Model();
}
public bool Value
{
get { return (bool)GetValue(ValueProperty); }
set { SetValue(ValueProperty, value); }
}
// Using a DependencyProperty as the backing store for Value. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value",
typeof(bool),
typeof(TestVM),
new FrameworkPropertyMetadata(
false,
FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
((sender, e) => ((TestVM)sender).Apply(e))));
private bool _suppress = false;
private void Apply(DependencyPropertyChangedEventArgs e)
{
if (_suppress) return;
try
{
_m.Value = this.Value;
}
catch
{
_suppress = true;
this.Value = _m.Value;
this.OnPropertyChanged(e);
}
finally
{
_suppress = false;
}
}
}
You don't need to use a DependencyObject as your ViewModel. You just need to implement INotifyPropertyChanged to get data binding support:
class TestVM
: INotifyPropertyChanged
{
private Model _m;
public TestVM()
{
_m = new Model();
}
public bool Value
{
get { return _m.Value; }
set
{
_m.Value = this.Value;
OnPropertyChanged("Value");
}
}
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
Note that if you expect the setter to throw exceptions, you may want to use an ExceptionValidationRule on the binding in your view.
Update: It sounds like your problem is that the Binding won't respond to PropertyChanged events within the call to set the source. One way to get around this is to use an asynchronous binding by setting IsAsync=True in the XAML for your binding. WPF will process the PropertyChanged event after it has finished updating the source value and won't think it is a reentrant call.
You can also get around this by using a Converter and turning off updates on PropertyChanged by doing UpdateSourceTrigger=LostFocus, but I don't think you would want that behavior.
I found a solution for my problem. I'm now deriving my own binding class that does the job.
public class ExceptionBinding : Binding
{
public ExceptionBinding(string name)
: base(name)
{
Construct();
}
public ExceptionBinding()
: base()
{
Construct();
}
private void Construct()
{
this.ValidatesOnExceptions = true;
this.UpdateSourceExceptionFilter = new UpdateSourceExceptionFilterCallback(OnException);
}
private object OnException(object bindExpression, Exception exception)
{
// ... custom error display ...
var exp = (BindingExpressionBase)bindExpression;
exp.UpdateTarget();
return null; // null needed to avoid display of the default error template
}
}
I create an object Custom as you can see below
public class GridViewModel
{
private List _listRowCust = new List();
public List ListRowCust
{
get { return _listRowCust; }
set { _listRowCust = value; }
}
}
public class RowCustom
{
private List<CellCustom> _listCellCustom = new List<CellCustom>();
public List<CellCustom> ListCellCustom
{
get { return _listCellCustom; }
set { _listCellCustom = value; }
}
public RowCustom() { }
}
I try to bind the custom object on the datagrid object available in silverlight4.
I wish to bind any cell on the datagrid. One line should identify by a row object and each cell by a cellCustom.
I use this code
textColumn = new DataGridTextColumn();
textColumn.Header = "RemainingWork";
textColumn.Binding = new Binding("Cell[0]"); //it's a supposed syntax possibility in fact I have 3 rows with 10 cells
GridElements.Columns.Add(textColumn);
GridElements.ItemsSource = e.GridViewModel.ListRowCust;
I don't find any explanation on How to custom the binding.
Do you have any idea?
Thank you
best regards,
Alexandre
I think you can only bind to public properties.
So CellCustom must have a public property to bind to, if that's the object used for the itemsSource, or data context.