Related
Wierd behaviour when passing values to and from second form.
ParameterForm pf = new ParameterForm(testString);
works
ParameterForm pf = new ParameterForm();
pf.testString="test";
doesn't (testString defined as public string)
maybe i'm missing something? Anyway I'd like to make 2nd variant work properly, as for now - it returns null object reference error.
Thanks for help.
Posting more code here:
calling
Button ParametersButton = new Button();
ParametersButton.Click += delegate
{
ParameterForm pf = new ParameterForm(doc.GetElementById(ParametersButton.Tag.ToString()));
pf.ShowDialog(this);
pf.test = "test";
pf.Submit += new ParameterForm.ParameterSubmitResult(pf_Submit);
};
definition and use
public partial class ParameterForm : Form
{
public string test;
public XmlElement node;
public delegate void ParameterSubmitResult(object sender, XmlElement e);
public event ParameterSubmitResult Submit;
public void SubmitButton_Click(object sender, EventArgs e)
{
Submit(this,this.node);
Debug.WriteLine(test);
}
}
result:
Submit - null object reference
test - null object reference
pf.ShowDialog(this); is a blocking call, so pf.Submit += new ParameterForm.ParameterSubmitResult(pf_Submit); is never reached: switch the order.
Submit(this,this.node); throws a null object reference because no event is assigned to it (see above). Generally, you should always check first: if (Submit != null) Submit(this,this.node);
You should change ``pf.ShowDialog(this);topf.Show(this);` so that your main form isn't disabled while your dialog box is open, if that's what you want, or use the model below (typical for dialog boxes.)
I'm not sure what pf_Submit is supposed to do, so this might not be the best way to go about it in your application, but it's how general "Proceed? Yes/No" questions work.
Button ParametersButton = new Button();
ParametersButton.Click += delegate
{
ParameterForm pf = new ParameterForm(testString);
pf.ShowDialog(this); // Blocks until user submits
// Do whatever pf_Submit did here.
};
public partial class ParameterForm : Form
{
public string test; // Generally, encapsulate these
public XmlElement node; // in properties
public void SubmitButton_Click(object sender, EventArgs e)
{
Debug.WriteLine(test);
this.Close(); // Returns from ShowDialog()
}
}
When you want to use your second variant, you have to use a getString()-Method, where you can put the e.g. "testString". The way you wrote it, "testString" should be a method (and got brackets).
EDIT (a bit more precise):
You could write:
pf.getString(testString);
, if "pf" is an instance of your own class, otherwise you had to look up, whether you can retrieve a String in this class.
the thing was in line order :)
pf.Submit += new ParameterForm.ParameterSubmitResult(pf_Submit);
and
pf.Test = "test";
should have been set before
pf.ShowDialog(this);
my mistake thingking that parameter can be passed after 2nd form was displayed
thnx for answers
I'm developing a WPF C# application and I have a strange behaviour in modification of objects. I try to explain it in general way.
Suppose that you have an object of a class described as follows:
public class A
{
int one;
bool two;
List<B> listofBObjects;
}
where B is:
public class B
{
int three;
int four;
}
I pass an instance of A class and an instance of B class from a window to another, only defining two variables of type A and B in the second window and passing them before the Show() method, with the following code, executed into an instance of window FirstWindow:
SecondWindow newWindow = new SecondWindow();
newWindow.instanceOfA = this.instanceOfA; //instanceOfA is of type A
newWindow.instanceOfB = this.instanceOfA.listOfBObjects[0]; //instanceOfB is of type B
newWindow.Show();
If I have to repeat this code twice(that is, opening twice the window), in the first execution everything works as expected, infact if I modify values in instanceOfB variable, I see the modification also in instanceOfA variable. But, in the second execution, the modification in instanceOfB does not affect instanceOfA...
The modifications are done in newWindow. For example:
this.instanceOfB.three++;
this.instanceOfB.four--;
Imagine that you are in the FirstWindow. Click on a button and SecondWindow opens, passing both variables as described above. In SecondWindow, do some modifications, click on OK and SecondWindow closes, returning control to FirstWindow. If I reclick on the same button, I reopen SecondWindow. If I do modifications now, they do not affect both variables.
I try to have a look (in VS2012) at both variables in the console with control expression and I see that, in the first pass of code, both variables changes when code above is executed but, in the second pass of code, only instanceOfB changes...
EDIT:
Following the code that I use to pass parameters to SecondWindow...types are explaind below
IntermediatePosition obj = ((FrameworkElement)sender).DataContext as IntermediatePosition; //IntermediatePosition is Class B
IntermediatePositionsSettingsWindow ips = new IntermediatePositionsSettingsWindow();
ips.currentIntermediatePosition = obj;//this is the instanceOfB
ips.idxOfIpToModify = obj.index;
ips.currentSingleProperty = this.currentPropertyToShow; //this is the instanceOfA object
ips.sideIndex = this.sideIndex;
ips.ShowDialog();
Consider that obj is given by a button selection into a datagrid, in which each row represents an IntermediatePosition object. In the datagrid, there is a column button and, clicking by buttons, IntermediatePositionsSettingsWindow is opened with the proper data
EDIT:
I've performed the folloqing check:
this.currentPropertyToShow.sides[this.sideIndex].intermediatePositionList[i].GetHashCode() == obj.GetHashCode()
where i is the index of related IntermediatePosition object. At first usage of IntermediatePositionsSettingsWindow the objects result equals, but in second usage they are different
Why this thing happens?
If it is needed any other clarification, I will edit the question
Thanks
It's difficult to give a proper answer to this, as there is insufficient code to correctly work out the issue. However, if you are databinding, then I believe you need to implement this interface. It is possible that you're issue is simply that you're model is not reflecting the changes to the screen.
I can't reproduce your problem. Here's a simplified representation of your class relation (as I understood from your question). Please let us know if this is correct:
public partial class MainWindow : Window
{
internal A instanceOfA;
internal B instanceOfB;
public MainWindow()
{
InitializeComponent();
instanceOfB = new B() { };
instanceOfA = new A() { listOfBObjects = new List<B>() { instanceOfB } };
}
private void Button_Click(object sender, RoutedEventArgs e)
{
SecondWindow newWindow = new SecondWindow();
newWindow.instanceOfA = this.instanceOfA; //instanceOfA is of type A
newWindow.instanceOfB = this.instanceOfA.listOfBObjects[0]; //instanceOfB is of type B
newWindow.Show();
}
}
public partial class SecondWindow : Window
{
internal A instanceOfA;
internal B instanceOfB;
public SecondWindow()
{
InitializeComponent();
Loaded += SecondWindow_Loaded;
}
void SecondWindow_Loaded(object sender, RoutedEventArgs e)
{
MessageBox
.Show(String.Format("{0}",
this.instanceOfB == this.instanceOfA.listOfBObjects[0]));
this.instanceOfB.three++;
this.instanceOfB.four--;
}
}
Note: this is not an answer, just trying to establish some common ground for further discussions, as comments don't leave you enough freedom for code samples.
Thanks to #pm_2 and #BillZhang comments, I found a row in my code in which this.currentPropertyToShowwas edited. After the returning back at first window, infact, I perform the refresh of the window, but it is not needed to edit this.currentPropertyToShow, so I have commented it and everything works!
Thanks everybody for precious comments and suggestions!
I have an About box in my C# project using Microsoft's Visual C# 2008 Express Edition named AboutBox1. I have made it look how I want it in the design view, but how do I make it appear when the About link in the Help menu is clicked?
This codes makes an About box appear, but it looks blank. It's not the one I designed.
private void aboutToolStripMenuItem_Click(object sender, EventArgs e)
{
AboutBox1 box = new AboutBox1();
box.ShowDialog();
}
Any thoughts or suggestions would be appreciated. Thanks.
Got it.
The about box is driven off of assembly properties for your project.
Go to Project -> 'ProjectName' Properties -> Assembly Information.
You set all of the information there.
If you try to set the information in the Property Explorer it will simply be over written at run time by what ever is in this window.
Cheers,
Mike
It sounds to me like a borked designer surface... have you hit save and rebuilt it? Perhaps close the IDE, reopen it, and check that your carefully designed form is still pretty?
BTW, when using ShowDialog you should also use using (since it doesn't Dispose() itself when shown with ShowDialog):
using(AboutBox1 box = new AboutBox1()) {
box.ShowDialog(this);
}
Did you remove the method-call to 'InitializeComponent' in the constructor of your AboutBox - form ?
Your constructor should at least look like this:
public partial class AboutBox : Form
{
public AboutBox()
{
InitializeComponent ();
}
}
Where the InitializeComponent method call should be the first line in the constructor.
If it appears but is blank, the problem is in AboutBox1. Show us some of that code.
I faced same problem before but I solved it by removing the statements below the InitializeComponent();
Default code:
partial class AboutBox1 : Form
{
public AboutBox1()
{
InitializeComponent();
this.Text = String.Format("About {0} {0}", AssemblyTitle);
this.labelProductName.Text = AssemblyProduct;
this.labelVersion.Text = String.Format("Version {0} {0}", AssemblyVersion);
this.labelCopyright.Text = AssemblyCopyright;
this.labelCompanyName.Text = AssemblyCompany;
this.textBoxDescription.Text = AssemblyDescription;
}
}
My final code:
partial class AboutBox1 : Form
{
public AboutBox1()
{
InitializeComponent();
}
}
I couldn't find the project / project name/ assembly properties.
But commenting out the lines after InitializeComponent(); worked for me.
This is how mine looks:
public frmAboutBox1()
{
InitializeComponent();
//this.Text = String.Format("About {0}", AssemblyTitle);
//this.labelMyFFEProductName.Text = AssemblyProduct;
//this.labelVersion.Text = String.Format("Version {0}", AssemblyVersion);
//this.labelCopyright.Text = AssemblyCopyright;
//this.labelCompanyName.Text = AssemblyCompany;
//this.textBoxDescription.Text = AssemblyDescription;
}
If you are an amateur like me, to find these lines, click the AboutBox in the project explorer, and hit the View Code button <>.
This is a .net problem with winforms, not asp.net.
I have a windows form with several tabs. I set data bindings of all controls when the form is loaded. But I have noticed that the data bindings of controls on the second tab do not work. Those bindings work only when the form is loaded and when I select the second tab. This brings the suspicion to me: data bindings work only when bound controls become visible.
Anyone can tell me whether this is true or not? It is not hard to test this but I would like to know some confirmation.
Thanks
You are correct. A data-bound control are not updated until the control is made visible.
The only reference I can find for this at the moment is this MSDN thread.
Your issue has to do with the behavior of the TabControl. See Microsoft bug report. I posted a workaround for that problem which subclasses the TabControl and 'Iniatalizes' all the tab pages when the control is created or the handle is created. Below is the code for the workaround.
public partial class TabControl : System.Windows.Forms.TabControl
{
protected override void OnHandleCreated(EventArgs e_)
{
base.OnHandleCreated(e_);
foreach (System.Windows.Forms.TabPage tabPage in TabPages)
{
InitializeTabPage(tabPage, true, Created);
}
}
protected override void OnControlAdded(ControlEventArgs e_)
{
base.OnControlAdded(e_);
System.Windows.Forms.TabPage page = e_.Control as System.Windows.Forms.TabPage;
if ((page != null) && (page.Parent == this) && (IsHandleCreated || Created))
{
InitializeTabPage(page, IsHandleCreated, Created);
}
}
protected override void OnCreateControl()
{
base.OnCreateControl();
foreach (System.Windows.Forms.TabPage tabPage in TabPages)
{
InitializeTabPage(tabPage, IsHandleCreated, true);
}
}
//PRB: Exception thrown during Windows Forms data binding if bound control is on a tab page with uncreated handle
//FIX: Make sure all tab pages are created when the tabcontrol is created.
//https://connect.microsoft.com/VisualStudio/feedback/details/351177
private void InitializeTabPage(System.Windows.Forms.TabPage page_, bool createHandle_, bool createControl_)
{
if (!createControl_ && !createHandle_)
{
return;
}
if (createHandle_ && !page_.IsHandleCreated)
{
IntPtr handle = page_.Handle;
}
if (!page_.Created && createControl_)
{
return;
}
bool visible = page_.Visible;
if (!visible)
{
page_.Visible = true;
}
page_.CreateControl();
if (!visible)
{
page_.Visible = false;
}
}
}
We've encountered a similar problem. We're trying to write to 2 bound, invisible fields so that we can change the format that we write to our dataset. This works fine when the objects are visible, but stops working when the visible property was changed to false.
To get round it, I added the following code:
// Stop our screen flickering.
chSplitContainer.Panel2.SuspendLayout();
// Make the bound fields visible or the binding doesn't work.
tbxValueCr.Visible = true;
tbxValueDb.Visible = true;
// Update the fields here.
<DO STUFF>
// Restore settings to how they were, so you don't know we're here.
tbxValueCr.Visible = false;
tbxValueDb.Visible = false;
chSplitContainer.Panel2.ResumeLayout();
I've struggled with this myself and concluded that the only workaround, besides subclassing apparently (see hjb417's answer), was to make the other tab visible. Switching to the other tab and going back to the previous immediately before the form is visible doesn't work. If you do not want to have the second tab visible, I've used the following code as a workaround:
this.tabControl.SelectedTab = this.tabPageB;
this.tabPageB.BindingContextChanged += (object sender, EventArgs e) => {
this.tabContainerMain.SelectedTab = this.tabPageA;
};
Assuming tabPageA is the visible tab, and tabPageB is the invisible one you want to initialize. This switches to pageB, and switches back once the data binding is complete. This is invisible to the user in the Form.
Still an ugly hack, but at least this works. Off course, he code gets even uglier when you have multiple tabs.
Sorry for necromancing this thread, but it is easy to force the invisible controls' databinding/handles to be ready using this method:
https://social.msdn.microsoft.com/Forums/vstudio/en-US/190296c5-c3b1-4d67-a4a7-ad3cdc55da06/problem-with-binding-and-tabcontrol?forum=winforms
Simply, let's say if your controls are in tab page tpg_Second (or tabCtl.TabPages[1]), before you do anything with their data, call this first:
tpg_Second.Show()
This will not activate any of the tab pages, but viola, the databinding of the controls should work now.
This is not something I've come across directly. However, you might be experiencing a problem with the BindingContext. Without more details it's hard to say, but if I were you I'd set a breakpoint and make sure the controls are all bound in the same context.
Based on the answers, I made this method that works for me:
public partial class Form1: Form
{
private void Form1_Load(object sender, EventArgs e)
{
...
forceBindTabs(tabControl1);
}
private void forceBindTabs(TabControl ctl)
{
ctl.SuspendLayout();
foreach (TabPage tab in ctl.TabPages)
tab.Visible = true;
ctl.ResumeLayout();
}
}
In addition to solving the problem, the tabs are loaded at the beginning and are displayed faster when the user clicks on them.
I have a list view that is periodically updated (every 60 seconds). It was anoying to me that i would get a flicker every time it up dated. The method being used was to clear all the items and then recreate them. I decided to instead of clearing the items I would just write directly to the cell with the new text. Is this a better approach or does anyone have a better solution.
The ListView control has a flicker issue. The problem appears to be that the control's Update overload is improperly implemented such that it acts like a Refresh. An Update should cause the control to redraw only its invalid regions whereas a Refresh redraws the control’s entire client area. So if you were to change, say, the background color of one item in the list then only that particular item should need to be repainted. Unfortunately, the ListView control seems to be of a different opinion and wants to repaint its entire surface whenever you mess with a single item… even if the item is not currently being displayed. So, anyways, you can easily suppress the flicker by rolling your own as follows:
class ListViewNF : System.Windows.Forms.ListView
{
public ListViewNF()
{
//Activate double buffering
this.SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.AllPaintingInWmPaint, true);
//Enable the OnNotifyMessage event so we get a chance to filter out
// Windows messages before they get to the form's WndProc
this.SetStyle(ControlStyles.EnableNotifyMessage, true);
}
protected override void OnNotifyMessage(Message m)
{
//Filter out the WM_ERASEBKGND message
if(m.Msg != 0x14)
{
base.OnNotifyMessage(m);
}
}
}
From: Geekswithblogs.net
In addition to the other replies, many controls have a [Begin|End]Update() method that you can use to reduce flickering when editing the contents - for example:
listView.BeginUpdate();
try {
// listView.Items... (lots of editing)
} finally {
listView.EndUpdate();
}
Here is my quick fix for a C# implementation that does not require subclassing the list views etc.
Uses reflection to set the DoubleBuffered Property to true in the forms constructor.
lvMessages
.GetType()
.GetProperty("DoubleBuffered", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)
.SetValue(lvMessages, true, null);
Update for 2021:
I got pinged on this old post with a comment and I would write this code differently now. Below is an extension method that will add a new method to a ListView to be able to set the double buffered property to true/false as required. This will then extend all list views and make it easier to call as reqired.
/// <summary>
/// Extension methods for List Views
/// </summary>
public static class ListViewExtensions
{
/// <summary>
/// Sets the double buffered property of a list view to the specified value
/// </summary>
/// <param name="listView">The List view</param>
/// <param name="doubleBuffered">Double Buffered or not</param>
public static void SetDoubleBuffered(this System.Windows.Forms.ListView listView, bool doubleBuffered = true)
{
listView
.GetType()
.GetProperty("DoubleBuffered", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic)
.SetValue(listView, doubleBuffered, null);
}
}
If this can help, the following component solved my ListView flickering issues with .NET 3.5
[ToolboxItem(true)]
[ToolboxBitmap(typeof(ListView))]
public class ListViewDoubleBuffered : ListView
{
public ListViewDoubleBuffered()
{
this.DoubleBuffered = true;
}
}
I use it in conjonction with .BeginUpdate() and .EndUpdate() methods where I do ListView.Items manipulation.
I don't understand why this property is a protected one...even in the .NET 4.5 (maybe a security issue)
Yes, make it double buffered. It will reduce the flicker ;) http://msdn.microsoft.com/en-us/library/system.windows.forms.listview.doublebuffered.aspx
Excellent question and Stormenent's answer was spot on. Here's a C++ port of his code for anyone else who might be tackling C++/CLI implementations.
#pragma once
#include "Windows.h" // For WM_ERASEBKGND
using namespace System;
using namespace System::Windows::Forms;
using namespace System::Data;
using namespace System::Drawing;
public ref class FlickerFreeListView : public ListView
{
public:
FlickerFreeListView()
{
//Activate double buffering
SetStyle(ControlStyles::OptimizedDoubleBuffer | ControlStyles::AllPaintingInWmPaint, true);
//Enable the OnNotifyMessage event so we get a chance to filter out
// Windows messages before they get to the form's WndProc
SetStyle(ControlStyles::EnableNotifyMessage, true);
}
protected:
virtual void OnNotifyMessage(Message m) override
{
//Filter out the WM_ERASEBKGND message
if(m.Msg != WM_ERASEBKGND)
{
ListView::OnNotifyMessage(m);
}
}
};
You can use the following extension class to set the DoubleBuffered property to true:
using System.Reflection;
public static class ListViewExtensions
{
public static void SetDoubleBuffered(this ListView listView, bool value)
{
listView.GetType()
.GetProperty("DoubleBuffered", BindingFlags.Instance | BindingFlags.NonPublic)
.SetValue(listView, value);
}
}
The simplest Solution would probably be using
listView.Items.AddRange(listViewItems.ToArray());
instead of
foreach (ListViewItem listViewItem in listViewItems)
{
listView.Items.Add(listViewItem);
}
This works way better.
Simple solution
yourlistview.BeginUpdate()
//Do your update of adding and removing item from the list
yourlistview.EndUpdate()
I know this is an extremely old question and answer. However, this is the top result when searching for "C++/cli listview flicker" - despite the fact that this isn't even talking about C++. So here's the C++ version of this:
I put this in the header file for my main form, you can choose to put it elsewhere...
static void DoubleBuffer(Control^ control, bool enable) {
System::Reflection::PropertyInfo^ info = control->GetType()->
GetProperty("DoubleBuffered", System::Reflection::BindingFlags::Instance
| System::Reflection::BindingFlags::NonPublic);
info->SetValue(control, enable, nullptr);
}
If you happen to land here looking for a similar answer for managed C++, that works for me. :)
This worked best for me.
Since you are editing the cell directly, the best solution in your case would be to simply refresh/reload that particular cell/row instead of the entire table.
You could use the RedrawItems(...) method that basically repaints only the specified range of items/rows of the listview.
public void RedrawItems(int startIndex, int endIndex, bool invalidateOnly);
Reference
This totally got rid of the full listview flicker for me.
Only the relevant item/record flickers while getting updated.
Cheers!
Try setting the double buffered property in true.
Also you could use:
this.SuspendLayout();
//update control
this.ResumeLayout(False);
this.PerformLayout();
In Winrt Windows phone 8.1 you can set the following code to fix this issue.
<ListView.ItemContainerTransitions>
<TransitionCollection/>
</ListView.ItemContainerTransitions>
For what it's worth, in my case, I simply had to add a call to
Application.EnableVisualStyles()
before running the application, like this:
private static void Main()
{
Application.EnableVisualStyles();
Application.Run(new Form1());
}
Otherwise, double buffering is not enough. Maybe it was a very old project and new ones have that setting by default...
If someone would still look an answer for this, I used a timer for a slight delay and it solved the problem nicely. I wanted to highlight (change colour) for the entire row on mouse move event, but I think it would work for item replacement etc. For me listView.BeginUpdate() and listView.EndUpdate() didn't work, DoubleBuffered property also didn't work, I have googled a lot and nothing worked.
private int currentViewItemIndex;
private int lastViewItemIndex;
private void listView_MouseMove(object sender, MouseEventArgs e)
{
ListViewItem lvi = listView.GetItemAt(e.X, e.Y);
if (lvi != null && lastViewItemIndex == -1)
{
listView.Items[lvi.Index].BackColor = Color.Green;
lastViewItemIndex = lvi.Index;
}
if (lvi != null && lastViewItemIndex != -1)
{
currentViewItemIndex = lvi.Index;
listViewTimer.Start();
}
}
private void listViewTimer_Tick(object sender, EventArgs e)
{
listView.BeginUpdate();
listView.Items[lastViewItemIndex].BackColor = Colour.Transparent;
listView.Items[currentViewItemIndex].BackColor = Colour.Green;
listView.EndUpdate();
lastViewItemIndex = currentViewItemIndex;
listViewTimer.Stop();
}