I have a Windows Forms application that I'm working on, but I'm having trouble when I start the application. The application should load saved information from a config file, and then check for new items. When I start the application, it starts looking for new items before it has finished loading saved items. Because of this the user is alerted of new items that are not really new, they just have not been loaded from the file yet.
The Form:
public class MainForm : Form
{
A a;
public MainForm()
{
InitializeComponent();
a = new A();
a.ItemsFound += new A.NewItemsFoundEventHandler(a_FoundItems);
a.ItemsLoaded += new A.ItemsLoadedEventHandler(a_ItemsLoaded);
a.LoadItems();
}
public void a_FoundItems(object sender, EventArgs e)
{
//Alert user of new items.
}
public void a_ItemsLoaded(object sender, EventArgs e)
{
//Update GUI with items loaded from file.
this.UpdateTheGUI_ThisIsNotARealMethodInMyProgram();
//Then look for new items.
a.CheckForUpdates();
}
}
The other object:
public class A
{
public A(){}
public void LoadItems()
{
//Load Items from save file...
OnItemsLoaded(this);
}
public void CheckForUpdates()
{
//Check for new items...
//If new items are found, raise ItemsFound event
OnNewItemsFound(this,new EventArgs());
}
public delegate void NewItemsFoundEventHandler(object sender, EventArgs e);
public event NewItemsFoundEventHandler ItemsFound;
protected void OnNewItemsFound(object sender, EventArgs e)
{
if(ItemsFound != null)
{
ItemsFound(sender,e);
}
}
public delegate void ItemsLoadedEventHandler(object sender, EventArgs e);
public event ItemsLoadedEventHandler ItemsLoaded;
protected void OnItemsLoaded(object sender)
{
if(ItemsLoaded != null)
{
ItemsLoaded(sender,new System.EventArgs());
}
}
}
Should I have object A call it's functions on a new thread, and lock so CheckForUpdates cannot be called if LoadItems is running, or is there a simpler way to do this that I'm missing?
EDIT:
I found the problem. I was clearing the List of items (so it would not grow forever), but I was only filling it with the newly found items. So every time I ran the application only the newest items where in the list, and all the older items were flushed out.
STUPID!!!
Thanks for the help though, and sorry for the crappy question.
Is there any reason why the check is not in the constructor?
public MainForm()
{
InitializeComponent();
a = new A();
a.ItemsFound += new A.NewItemsFoundEventHandler(a_FoundItems);
a.ItemsLoaded += new A.ItemsLoadedEventHandler(a_ItemsLoaded);
a.LoadItems();
a.CheckForUpdates();
}
Hmm, from the code you've posted i dont see a problem, especially assuming all this runs on the ui thread.. can you post the code for the loading of items?
Perhaps the loading it self is firing the ItemsFound event? You could do the subscription for ItemsFound in the eventhandler for ItemsLoaded instead of in the constructor.
public class MainForm : Form
{
A a;
public MainForm()
{
InitializeComponent();
a = new A();
a.ItemsLoaded += new A.ItemsLoadedEventHandler(a_ItemsLoaded);
a.LoadItems();
}
public void a_ItemsLoaded(object sender, EventArgs e)
{
a.ItemsFound += new A.NewItemsFoundEventHandler(a_FoundItems);
a.CheckForUpdates();
}
}
Related
Can someone please illustrate for me how to set up a logic like this:
I have a WPF Control. When a button is pressed it does one of the two possible things.
A. It checks if a different WPF Window has been loaded. If it was, it triggers that window's Print method.
B. It checks if a different WPF Window has been loaded. If it was not, it instantiates that window and then triggers its Print method.
I struggle to understand the events system between two WPF Controls/Windows. It's a relatively new thing for me, so I would appreciate if someone walked me through this.
Ps. This is not a homework assignment, but rather a new hobby of mine. If its a totally noob question then just point me to a resource so I can educate myself.
Cheers!
First of all, what is the way by which you will check if new Window opened is what you need it to be ?
You might do this by comparing their Handle or their Type (public class MyWindowWithPrintMethod : Window).
There can be multiple ways of doing this.
I suggest my simple way, focusing on the WPF way, to solve your purpose in easiest way possible.
MyWindowWithPrintMethod obj_MyWindowWithPrintMethod;
private void btnNewWindow_Click(object sender, RoutedEventArgs e)
{
obj_MyWindowWithPrintMethod = new MyWindowWithPrintMethod();
obj_MyWindowWithPrintMethod.Show();
}
private void btnCheckNewWindow_Click(object sender, RoutedEventArgs e)
{
WindowInteropHelper tgtWindow = new WindowInteropHelper(obj_MyWindowWithPrintMethod);
foreach (Window w in Application.Current.Windows)
{
// Compare Handle
WindowInteropHelper wih = new WindowInteropHelper(w);
if (wih.Handle == tgtWindow.Handle)
{
((MyWindowWithPrintMethod)w).Print();
}
// Compare Type
if (w.GetType() == typeof(MyWindowWithPrintMethod))
{
((MyWindowWithPrintMethod)w).Print();
}
}
}
MyWindowWithPrintMethod.cs
public class MyWindowWithPrintMethod : Window
{
public void Print()
{
MessageBox.Show("Print invoked !");
}
}
This answer from this question about events from 2 windows may help:
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.Loaded += new RoutedEventHandler(MainWindow_Loaded);
}
void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
Child childWindow = new Child();
childWindow.MyEvent += new EventHandler(childWindow_MyEvent);
childWindow.ShowDialog();
}
void childWindow_MyEvent(object sender, EventArgs e)
{
// handle event
MessageBox.Show("Handle");
}
}
Child window
public partial class Child : Window
{
// define event
public event EventHandler MyEvent;
protected void OnMyEvent()
{
if (this.MyEvent != null)
this.MyEvent(this, EventArgs.Empty);
}
public Child()
{
InitializeComponent();
this.Loaded += new RoutedEventHandler(Child_Loaded);
}
void Child_Loaded(object sender, RoutedEventArgs e)
{
// call event
this.OnMyEvent();
}
}
The above code shows how to set up an event from one window to another. But, you might want to simply call a method in that other window instead. For example:
public void AddNewUser()
{
Window2 window = new Window2();
if (window.ShowDialog() == true)
{
// Update DataGrid
RefreshDataGrid();
}
}
If you are determined to stick with events, then you should read up on WPF routed events.
I made a class so when the user selects item from listbox it uninstalls that item, except the problem is I can't access the list box. I tried public aswell, but in the code of form1.cs the only thing clostest to that list box is
keep in mind name of listbox is ProgramslistBox
Ok guys I re edited this post;
private void button1_Click(object sender, EventArgs e)
{
if(ProgramsListbox.SelectedIndex == -1)
{
MessageBox.Show("Please select an item to uninstall!");
}
else
{
ProgramsListbox_SelectedIndexChanged("",EventArgs.Empty);
}
}
this code is the FORM1.CS class, and I have another class called UninstallItem.cs is where I want my code to be, this below is my other class
namespace PC_TECH_Registery_Cleaner
{
class UninstallItem
{
public void uninstallSelectedItem()
{
Form1 c = new Form1();
}
}
}
And this below is still in my FORM1.CS class, I was experimenting with it :
public void ProgramsListbox_SelectedIndexChanged(object sender, EventArgs e)
{
//this will access the Uninstall item class so we can uninstall selected item.
UninstallItem c = new UninstallItem();
c.uninstallSelectedItem();
}
Within your Form1.cs create instance of UnIstallItem class and use it. Then on Button Click call "RemoveSelected" method of UnInstaItem class by passing programsListBox to it and it should remove the selected item.
public class Form1:Form
{
ListBox ProgramsListbox;
UninstallItem unistall;
public Form1(){
InitializeComponent();
uninstall = new UninstallItem();
button1.Click+= button1_Click;
}
void button1_Click(object sender, EventArgs e){
unistall.RemoveSelected(ProgramsListbox);
}
}
Then in your external class;
public class UninstallItem{
public UninstallItem{}
public void RemoveSelected(ListBox list)
{
if(list.SelectedIndex==-1)
{
MessageBox.Show("Please Select Item from List");
return;
}
list.Items.RemoveAt(list.SelectedIndex);
}
}
The 2 easy ways to think about this are either
Call the method in your class from the event handler in your form
Have a method on your class which matches the signature of an event handler, and subscribe to the event.
The first requires no major change
private MyClass myClass = new MyClass();
public void ProgramsListbox_SelectedIndexChanged(object sender, EventArgs e)
{
myClass.DoSomething();
}
The second requires your class to have a specific method that matches the signature of that event handler currently in your form
public class MyClass
{
public void DoSomething(object sender, EventArgs e)
{
var listBox = (ListBox)sender;
// read selected index perhaps, or selected item maybe
}
}
And then in your form
private MyClass myClass = new MyClass();
protected override void OnLoad(EventArgs e)
{
this.ProgramsListBox.SelectedIndexChanged += myClass.DoSomething;
}
I'm quite new in C#, so I'm struggling with this more than two days. I hope that some one can help me out with this one.
Below some simplified code from my application.
I want to pass a List from Form1 to Form2 using delegate and event.
How can I do this? I read tons of explanations about events and delegates, but I still can't figure it out, how this really works.
Form1:
public delegate List<string> ProfileImportEventHandler();
public event ProfileImportEventHandler ProfileImported;
private void btnImport_Click(object sender, EventArgs e)
{
// raise an event
OnProfileImported();
}
protected virtual void OnProfileImported()
{
if (ProfileImported != null) // check if there are subscribers
{
ProfileImported();
}
}
Form2:
public partial class Form2 : Form
{
Form1 frm1;
public Form1()
{
// Constructor logic
frm1.ProfileChanged += new Form1.ProfileImportEventHandler(Form1_OnProfileImported);
}
}
List<string> Form1_OnProfileImported()
{
// TO DO
}
UPDATE
None of the solutions worked so far. Here is what I have already tried:
Form 2
// use generic list for profiles that will be imported from USB-Stick
private List<string> profilePaths = new List<string>();
public delegate void ProfileImportEventHandler(object sender, ProfileImportEventArgs e);
public event ProfileImportEventHandler ProfileImported;
public delegate void ImportButtonClickedEventHandler();
public event ImportButtonClickedEventHandler ButtonImportClicked;
public delegate void HaveDataDelegate(IList<string> data);
public event HaveDataDelegate HaveData;
//....
private void btnImport_Click(object sender, EventArgs e)
{
// do something...
// raise an event
var ea = new ProfileImportEventArgs(profilePaths);
OnProfileImported(ea);
OnButtonImportClicked();
// When there is data:
var copy = HaveData; // Use copy to avoid race conditions
if (copy != null)
{
copy(profilePaths);
}
// close form
this.Dispose();
}
protected virtual void OnProfileImported(ProfileImportEventArgs ea)
{
if (ProfileImported != null) // check if there are any subscribers
{
ProfileImported(this, ea);
}
}
protected virtual void OnButtonImportClicked()
{
if (ButtonImportClicked != null)
{
// fire event
ButtonImportClicked();
}
}
Form 1
public partial class frm_1 : Form
{
// child form
frm_2 frm2;
public frm_1()
{
InitializeComponent();
// do something...
// not sure if this is correct code and the correct place for it
frm2 = new frm_2();
frm2.ProfileImported += new frm_2.ProfileImportEventHandler(frm2_OnProfileImported);
//frm2.ProfileImported += frm2_OnProfileImported;
frm2.ButtonImportClicked += new frm_2.ImportButtonClickedEventHandler(frm2_ButtonImportClicked);
// In creation/init:
frm2.HaveData += DataFromForm2;
}
void frm2_OnProfileImported(object sender, ProfileImportEventArgs e)
{
// do something
}
void frm2_ButtonImportClicked()
{
// do something
}
private void DataFromForm2(IList<string> data)
{
// Process the data from Form2.
}
}
What am I still missing? Thank you for your help.
frm1.ProfileChanged += new Form1.ProfileImportEventHandler(Form1_OnProfileImported);
[…]
List<string> frmLoadProfileUSB_OnProfileImported()
First those names do not match. Second, with matching signatures you do not need (since C#2 if I recall correctly) to explicitly create the delegate. Thus:
frm1.ProfileChanged += frmLoadProfileUSB_OnProfileImported;
However, I think you have the event in the wrong place. It appears it is Form2 trying to pass data to Form1. Thus the event needs to be on Form2, with a delegate that is passed the data. Thus:
In Form2
public delegate void HaveDataDelegate(IList<string> data);
public event HaveDataDelegate HaveData;
// When there is data:
var copy = HaveData; // Use copy to avoid race conditions
if (copy != null) {
copy(data);
}
In Form1
// In creation/init:
Form2Instance.HaveData += DataFromForm2;
private void DataFromForm2(IList<string> data) {
// Process the data from Form2.
}
It's better not to use strong coupling.
So best solution here would be to store data in database or create proxy-object (class/struct).
like:
public (static) class ProfileChangesMonitor
{
...your logic here
}
If you want to use event handlers, you should follow the general pattern, defining a class that inherits EventArgs (supposing you want to involve a list in the event) in this way:
// Event Args
public class ProfileImportEventArgs : EventArgs {
private IList<string> list;
public ProfileImportEventArgs(IList<string> list) {
this.list = list;
}
public IList<string> List {
get {
return this.list;
}
}
}
// Event Handler Delegate
public delegate void ProfileImportEventHandler(object sender, ProfileImportEventArgs e);
// Form1:
public event ProfileImportEventHandler ProfileImported;
// ...
private void btnImport_Click(object sender, EventArgs e)
{
// raise an event
List<string> list = new List();
// Add something to list if needed
var ea = new ProfileImportEventArgs(list);
OnProfileImported(ea);
// Use ea.list here if necessary
}
protected virtual void OnProfileImported(ProfileImportEventArgs ea)
{
if (ProfileImported != null) { // check if there are subscribers
ProfileImported(this, ea);
}
}
// Form2:
public partial class Form2 : Form
{
Form1 frm1;
public Form1()
{
// Constructor logic
// TODO: Instantiate frm1 first.
frm1.ProfileImported += new Form1.ProfileImportEventHandler(Form1_OnProfileImported);
}
}
private void frmLoadProfileUSB_OnProfileImported(object sender, ProfileImportEventArgs e)
{
// Use and/or modify e.List if needed
}
I'm actually learning (the hard way) c# and been fighting for days with a problem :
I'm writing my first c# application with WPF (dotNet 4.0). When I click on a button, a BackgroundWorker thread is used and call a method from an external class, this way my UI don't freeze -> my method run as expected.
Then I tried to update a ListView control from thos external class to get some kind of progress (text) and I miserably failed.
I understand that I need to use a delegate and the dispatcher to update my control.
I tried to use the solution offered here How to update UI from another thread running in another class . (I cannot comment on it because of my low rep) and I miss some parts of the puzzle.
What the YourEventArgs(status) is referring to ? I just don't get the way to fire an event and pass the content back to my UI while my method is running inside the BGW.
So far I have this piece of code (Updated from answer):
namespace AppMain
{
public partial class MainWindow
{
BackgroundWorker AppWorker = new BackgroundWorker();
public MainWindow()
{
InitializeComponent();
AppWorker.WorkerSupportsCancellation = true;
AppWorker.DoWork += AppWorker_DoWork;
AppWorker.RunWorkerCompleted += AppWorker_RunWorkerCompleted;
}
private void btnLoad_Click(object sender, RoutedEventArgs e)
{
lstTest.Items.Add("Processing data...");
AppWorker.RunWorkerAsync();
}
public void AppWorker_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
SetXmlData xml = new SetXmlData();
xml.ProgressUpdate += (s, evt) =>
{
Dispatcher.BeginInvoke((Action)(() =>
{
lstTest.Items.Add("this is a test : " + evt.myData); //how to retrieve the myData property from evt ?
}));
};
xml.FlushData();
}
public void AppWorker_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e)
{
if (!(e.Cancelled))
{
lstTest.Items.Add("Done");
}
else
{
MessageBox.Show("Cancelled");
}
}
}
}
SetXmlData.cs
namespace AppMain
{
public class SetXmlData
{
public event EventHandler ProgressUpdate;
//update method
public void update(object input)
{
if (ProgressUpdate != null)
ProgressUpdate(this, new YourEventArgs { myData = (string)input });
}
//calculation method
public void FlushData()
{
MessageBox.Show("this is a test !");
update("test");
}
}
public class YourEventArgs : EventArgs
{
public string myData { get; set; }
}
}
Thanks for your help.
You can simply Invoke the ProgressUpdate event from the FlushData() method.
Simply call:
If (ProgressUpdate !=null )
{
ProgressUpdate(this,new YourEventArgs())
}
this is the source instance where the event originated from.
You could just create YourEventArgs by inheriting from EventArgs class.
public class YourEventArgs : EventArgs
{
//Put any property that you want to pass back to UI here.
}
When the event gets raised in the UI:
RaiseEvent.ProgressUpdate += (s, e) =>
{
Dispatcher.BeginInvoke((Action)(() =>
{
lstTest.Items.Add("this is a test : ");
//Add items to your UI control here...
}));
};
e will be of type YourEventArgs.
On a side note, you should never touch UI thread from a diffent thread (like background worker thread in your example). Since your event-handler already does the Dispatcher.BeginInvoke, that's safe.
Also, your ProgressUpdate event should be inside of your class SetXmlData.
try get;set; Example:
Form1:
public partial class Form1 : Form
{
static public string gettext { get; set; }
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
Class1.send(); //call to class function
textBox1.Text = gettext; //items.add(gettext)
}
}
Class1:
class Class1
{
static public void send()
{
Form1.gettext = "Marko"; //Set gettext to string "Marko"
}
}
I added an event handler to my code and it broke all access to the CollectionViewSources in the SystemHTA class saying "The calling thread cannot access this object because a different thread owns it". My class was working when "this.systemHTA = new SystemHTA();" was placed outside of the DeviceManager_StateChanged() function.
public partial class MainWindow : Window
{
private DeviceManager DeviceManager = DeviceManager.Instance;
public SystemHTA systemHTA;
public MainWindow()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
DeviceManager.StateChanged += new EventHandler<DeviceManagerStateChangedEventArgs>(DeviceManager_StateChanged);
DeviceManager.Initialize();
}
void DeviceManager_StateChanged(object sender, DeviceManagerStateChangedEventArgs e)
{
if (e.State == DeviceManagerState.Operational)
{
this.systemHTA = new SystemHTA();
}
}
private void button1_Click(object sender, RoutedEventArgs e)
{
this.systemHTA.GetViewSourceTest();
}
}
public class SystemHTA
{
private CollectionViewSource _deviceTestSource;
public SystemHTA()
{
_deviceTestSource = new CollectionViewSource();
_deviceTestSource.Source = CreateLoadData<HWController>.ControllerCollection;
}
public void GetViewSourceTest()
{
ListCollectionView view = (ListCollectionView)_deviceTestSource.View; //This creates an error saying a thread already owns _deviceTestSource
}
}
This is not about 'Thread Locking' but about the well known problem that a GUI (either WPF or WinForms) is not threadsafe and in a Debug build there is active checking for cross-thread calls.
So you already know the solution: create the SystemHTA object on the main thread. Your problem may shift to loading it from the DeviceMgr stuff, you may have to use Control.Dispatcher.Invoke() here.
I ended up replacing the CollectionViewSource with an ObservableCollection and everything works fine.