Question:
I have an Image control with it's source bound to a property on an object(string url to an image). After making a service call, i update the data object with a new URL. The exception is thrown after it leaves my code, after invoking the PropertyChanged event.
The data structure and the service logic are all done in a core dll that has no knowledge of the UI. How do I sync up with the UI thread when i cant access a Dispatcher?
PS: Accessing Application.Current.RootVisual in order to get at a Dispatcher is not a solution because the root visual is on a different thread(causing the exact exception i need to prevent).
PPS: This only is a problem with the image control, binding to any other ui element, the cross thread issue is handled for you.
Solution:1
System.Windows.Deployment.Current.Dispatcher.BeginInvoke(() => {...}); Also look here.
Solution:2
Have you tried implementing INotifyPropertyChanged?
Solution:3
The property getter for RootVisual on the Application class has a thread check which causes that exception. I got around this by storing the root visual's dispatcher in my own property in my App.xaml.cs:
public static Dispatcher RootVisualDispatcher { get; set; } private void Application_Startup(object sender, StartupEventArgs e) { this.RootVisual = new Page(); RootVisualDispatcher = RootVisual.Dispatcher; } If you then call BeginInvoke on App.RootVisualDispatcher rather than Application.Current.RootVisual.Dispatcher you shouldn't get this exception.
Solution:4
I ran into a similar issue to this, but this was in windows forms:
I have a class that has it's own thread, updating statistics about another process, there is a control in my UI that is databound to this object. I was running into cross-thread call issues, here is how I resolved it:
Form m_MainWindow; //Reference to the main window of my application protected virtual void OnPropertyChanged(string propertyName) { if(PropertyChanged != null) if(m_MainWindow.InvokeRequired) m_MainWindow.Invoke( PropertyChanged, this, new PropertyChangedEventArgs(propertyName); else PropertyChanged(this, new PropertyChangedEventArgs(propertyName); } This seems to work great, if anyone has suggestions, please let me know.
Solution:5
When ever we want to update UI related items that action should happen in the UI thread else you will get an invalid cross thread access exception
Deployment.Current.Dispatcher.BeginInvoke( () => { UpdateUI(); // DO the actions in the function Update UI }); public void UpdateUI() { //to do :Update UI elements here }
Solution:6
The INotifyPropertyChanged interface is used to notify clients, typically binding clients, that a property value has changed.
For example, consider a Person object with a property called FirstName. To provide generic property-change notification, the Person type implements the INotifyPropertyChanged interface and raises a PropertyChanged event when FirstName is changed.
For change notification to occur in a binding between a bound client and a data source, your bound type should either:
Implement the INotifyPropertyChanged interface (preferred).
Provide a change event for each property of the bound type.
Do not do both.
Example:
using System; using System.Collections.Generic; using System.ComponentModel; using System.Drawing; using System.Runtime.CompilerServices; using System.Windows.Forms; // Change the namespace to the project name. namespace TestNotifyPropertyChangedCS { // This form demonstrates using a BindingSource to bind // a list to a DataGridView control. The list does not // raise change notifications. However the DemoCustomer type // in the list does. public partial class Form1 : Form { // This button causes the value of a list element to be changed. private Button changeItemBtn = new Button(); // This DataGridView control displays the contents of the list. private DataGridView customersDataGridView = new DataGridView(); // This BindingSource binds the list to the DataGridView control. private BindingSource customersBindingSource = new BindingSource(); public Form1() { InitializeComponent(); // Set up the "Change Item" button. this.changeItemBtn.Text = "Change Item"; this.changeItemBtn.Dock = DockStyle.Bottom; this.changeItemBtn.Click += new EventHandler(changeItemBtn_Click); this.Controls.Add(this.changeItemBtn); // Set up the DataGridView. customersDataGridView.Dock = DockStyle.Top; this.Controls.Add(customersDataGridView); this.Size = new Size(400, 200); } private void Form1_Load(object sender, EventArgs e) { // Create and populate the list of DemoCustomer objects // which will supply data to the DataGridView. BindingList<DemoCustomer> customerList = new BindingList<DemoCustomer>(); customerList.Add(DemoCustomer.CreateNewCustomer()); customerList.Add(DemoCustomer.CreateNewCustomer()); customerList.Add(DemoCustomer.CreateNewCustomer()); // Bind the list to the BindingSource. this.customersBindingSource.DataSource = customerList; // Attach the BindingSource to the DataGridView. this.customersDataGridView.DataSource = this.customersBindingSource; } // Change the value of the CompanyName property for the first // item in the list when the "Change Item" button is clicked. void changeItemBtn_Click(object sender, EventArgs e) { // Get a reference to the list from the BindingSource. BindingList<DemoCustomer> customerList = this.customersBindingSource.DataSource as BindingList<DemoCustomer>; // Change the value of the CompanyName property for the // first item in the list. customerList[0].CustomerName = "Tailspin Toys"; customerList[0].PhoneNumber = "(708)555-0150"; } } // This is a simple customer class that // implements the IPropertyChange interface. public class DemoCustomer : INotifyPropertyChanged { // These fields hold the values for the public properties. private Guid idValue = Guid.NewGuid(); private string customerNameValue = String.Empty; private string phoneNumberValue = String.Empty; public event PropertyChangedEventHandler PropertyChanged; // This method is called by the Set accessor of each property. // The CallerMemberName attribute that is applied to the optional propertyName // parameter causes the property name of the caller to be substituted as an argument. private void NotifyPropertyChanged([CallerMemberName] String propertyName = "") { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } // The constructor is private to enforce the factory pattern. private DemoCustomer() { customerNameValue = "Customer"; phoneNumberValue = "(312)555-0100"; } // This is the public factory method. public static DemoCustomer CreateNewCustomer() { return new DemoCustomer(); } // This property represents an ID, suitable // for use as a primary key in a database. public Guid ID { get { return this.idValue; } } public string CustomerName { get { return this.customerNameValue; } set { if (value != this.customerNameValue) { this.customerNameValue = value; NotifyPropertyChanged(); } } } public string PhoneNumber { get { return this.phoneNumberValue; } set { if (value != this.phoneNumberValue) { this.phoneNumberValue = value; NotifyPropertyChanged(); } } } } } Note:If u also have question or solution just comment us below or mail us on toontricks1994@gmail.com
EmoticonEmoticon