We Keep Coding

C# Moving own controls around and make them droppable

A good morning to you all!
Yesterday I ran into a problem while trying to implement a custom DragDrop for my own controls in a WinForms application.
I have a form which can dynamically create instances of two of my own controls. These controls consist of some controls themselves, such as buttons, labels and listboxes/treeviews. The controls serve as a representation for a certain dataset. Now, we all know the class diagrams in VS. There you have these boxes representing classes. You can move the boxes around on the canvas by doing - what I would call - dragging them around, much like you would drag around files. To accomplish this with my own controls I have done the following:
public partial class MyControl: UserControl
{
private Control activeControl;
private void GeneralMouseDown(MouseEventArgs e)
{
activeControl = this;
previousLocation = e.Location;
Cursor = Cursors.Hand;
}
private void GeneralMouseMove(Control sender, MouseEventArgs e)
{
if (activeControl == null || activeControl != sender)
return;
var location = activeControl.Location;
location.Offset(e.Location.X - previousLocation.X, e.Location.Y - previousLocation.Y);
activeControl.Location = location;
}
private void GeneralMouseUp()
{
activeControl = null;
Cursor = Cursors.Default;
}
}
The controls on my control which I want to "grab" for dragging MyControl have their MouseDown-, MouseMove- and MouseUp-events pointing to these three methods. As a result I can move my control about on the form freely, just as I want to.
Here comes the tricky bit:
The datasets I have controls for can be in hierarchical dependencies, which means, one control represents detailling of a component of the other, which is why my controls have Listboxes or TreeViews. To establish such a hierarchical dependency I would very much like to DragDrop the lower-order-control on the listbox of my higher-order-control, causing data to be transfered.
I know how to set up my DragEnter and DragDrop methods for the listbox, as I have done so previously with files. Just for completeness:
private void lst_MyControl_DragEnter(object sender, DragEventArgs e)
{
if (e.Data.GetDataPresent(typeof(MyControl)))
e.Effect = DragDropEffects.Move;
else e.Effect = DragDropEffects.None;
}
Here's the problem: As I am moving my control about (which gets repainted at every position, giving a very much wanted effect!), when I "drag" it over the target-listbox, the DragEnter-event does not get fired. I thought I could work around this problem by telling Windows "Hey, I'm, Dragging'n'Dropping here!", thus adding to my GeneralMouseDown-method:
this.DoDragDrop(this, DragDropEffects.Move);
This, on the one hand, gets the DragEnter-event to fire => Yeah! On the other hand is the moving-around-part only working after I release the mouse, causing the control to hang on the mousepointer forever => Anti-Yeah!
Here's the question: Is there a way, to have both actions at the same time? So that I can move my control around, seing it at every position as I do now and fire the DragEnter-event when I get to that area of the other control?

Moving your Control around interferes with the automatic DragDrop handling.
I'd recommend to staying with the normal DragDrop procedures, that is leaving all visuals to the system: It will display a cursor that indicates when a valid target is entered, then change to one that indicates the operation.
You need just 3 lines, no hassle and the user won't seen bulky controls moving around.
Here is a version where I drag a PictureBox onto a ListBox:
private void listBox1_DragEnter(object sender, DragEventArgs e)
{
e.Effect = DragDropEffects.Copy;
}
private void listBox1_DragDrop(object sender, DragEventArgs e)
{
listBox1.Items.Add( e.Data.GetData(DataFormats.Text));
}
private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
{
if (e.Button == System.Windows.Forms.MouseButtons.Left)
pictureBox1.DoDragDrop(pictureBox1.ImageLocation, DragDropEffects.Copy);
}
Obviously you will set up and receive your data in your own ways..
Edit:
Now, if on the other hand you need to move controls around to rearrange them, maybe you should give up on Drag&Drop to handle the additional data transfers and code this portion on your own as well. You could use the MouseEnter event of a receiving control..

After a bit of fiddeling I did it. I switched the level on which the dragging is handled.
First I need just the MouseDown-event
public Point GrabPoint;
private void GeneralMouseDown(MouseEventArgs e)
{
GrabPoint = e.Location;
this.DoDragDrop(this, DragDropEffects.Move);
}
I set the point where I grab the control and initiate a DragDrop. On my form I handle all the dragging:
private void frmMain_DragEnter(object sender, DragEventArgs e)
{
if (e.Data.GetDataPresent(typeof(MyControl1)) || e.Data.GetDataPresent(typeof(MyControl2)) || e.Data.GetDataPresent(typeof(MyControl3)))
e.Effect = DragDropEffects.Move;
else e.Effect = DragDropEffects.None;
}
private void frmMain_DragOver(object sender, DragEventArgs e)
{
Point DragTarget = new Point(e.X, e.Y);
Point GrabPoint = new Point(0, 0);
if (e.Data.GetDataPresent(typeof(MyControl1)))
GrabPoint = ((MyControl1)e.Data.GetData(typeof(MyControl1))).GrabPoint;
else if (e.Data.GetDataPresent(typeof(MyControl2)))
GrabPoint = ((MyControl2)e.Data.GetData(typeof(MyControl2))).GrabPoint;
else if (e.Data.GetDataPresent(typeof(MyControl3)))
GrabPoint = ((MyControl3)e.Data.GetData(typeof(MyControl3))).GrabPoint;
DragTarget.X -= GrabPoint.X;
DragTarget.Y -= GrabPoint.Y;
DragTarget = this.PointToClient(DragTarget);
if (e.Data.GetDataPresent(typeof(MyControl1)))
((MyControl1)e.Data.GetData(typeof(MyControl1))).Location = DragTarget;
else if (e.Data.GetDataPresent(typeof(MyControl2)))
((MyControl2)e.Data.GetData(typeof(MyControl2))).Location = DragTarget;
else if (e.Data.GetDataPresent(typeof(MyControl3)))
((MyControl3)e.Data.GetData(typeof(MyControl3))).Location = DragTarget;
}
At the moment I don't need the DragDrop-event, since nothing should happen when any control is dropped on the form. This way I always paint my control while it is being dragged => Yeah!
The next part is easy: Since I am really dragging the control, this bit of code does DragDrop-handling on my listbox Edit: ListView:
private void lst_SubControls_DragEnter(object sender, DragEventArgs e)
{
if (e.Data.GetDataPresent(typeof(MyControl2)))
e.Effect = DragDropEffects.Move;
else e.Effect = DragDropEffects.None;
}
private void lst_SubControls_DragDrop(object sender, DragEventArgs e)
{
lst_SubControls.Items.Add(((MyControl2)e.Data.GetData(typeof(MyControl2))).SpecificDrive);
((MyControl2)e.Data.GetData(typeof(MyControl2))).DeleteThisControl();
}
This results in an entry added to the list and deletion of the dragged control. At this point there could be a check, wether the ctrl-key is pressed to copy the contents and not to delete the control.

flow panel with listview

I'm creating listviews in a flowpanel at run time which later will accept drag and dropped files. the reason being is i want these to act as folders so a user double clicks and gets a window displaying the contents.
i'm having difficulty setting up the events for my listviews as they are added.
how do i create some events (like MouseDoubleClick and DragDrop) dynamically for each added listview? can i create a single function for both of these events and have listview1, listview2, listviewX use it?
i have a button that is adding the listviews, which works fine. please advise, i apologize if this is too conceptual and not exact enough.
private void addNewWOButton_Click(object sender, EventArgs e)
{
ListView newListView = new ListView();
newListView.AllowDrop = true;
flowPanel.Controls.Add(newListView);
}

You would have to have the routine already created in your code:
private void listView_DragDrop(object sender, DragEventArgs e) {
// do stuff
}
private void listView_DragEnter(object sender, DragEventArgs e) {
// do stuff
}
and then in your routine, your wire it up:
private void addNewWOButton_Click(object sender, EventArgs e)
{
ListView newListView = new ListView();
newListView.AllowDrop = true;
newListView.DragDrop += listView_DragDrop;
newListView.DragEnter += listView_DragEnter;
flowPanel.Controls.Add(newListView);
}
You would have to check who the "sender" is if you need to know which ListView control is firing the event.
You can also just use a lambda function for simple things:
newListView.DragEnter += (s, de) => de.Effect = DragDropEffects.Copy;

Just make sure to unwire the events with -= if you also remove the ListViews dynamically.
To answer the other half of your question, you can use a single handler for any event, from any source, that has the handler's signature. In the body of the handler, you just have to check the sender argument to determine which control raised the event.
You need a way to tell one control from a different one of the same class, however. One way to do this is to make sure to set the Name property on each control when you create it; e.g., newListView.Name = "FilesListView".
Then, before you do anything else in your event handler, check the sender.
private void listView_DragDrop(object sender, DragEventArgs e) {
ListView sendingListView = sender as ListView;
if(sendingListView == null) {
// Sender wasn't a ListView. (But bear in mind it could be any class of
// control that you've wired to this handler, so check those classes if
// need be.)
return;
}
switch(sendingListView.Name) {
case "FilesListView":
// do stuff for a dropped file
break;
case "TextListView":
// do stuff for dropped text
break;
.....
}
}

AllowDrop property not working for ToolStripItems

I have successfully created DragDrop functionality with user controls. Now I am trying to allow DragDrop functionality on some components such as ToolStripButton.
The base class, ToolStripItem, supports AllowDrop and the DragEnter/DragDrop events...
ToolStripButton hides these properties in the designer, but they are publicly accessable.
Originally I tried doing the following for each ToolStripButton:
button.AllowDrop = true;
button.DragEnter += new DragEventHandler(button_DragEnter);
button.DragDrop += new DragEventHandler(button_DragDrop);
However, the events were not ever firing. These buttons are contained within a MenuStrip, so I changed the MenuStrip.AllowDrop to true. Then I started getting DragEnter and DragDrop events, but the DragDrop event would fail due to a threading/invoke problem when accessing the Tag property of the ToolStripItem.
The ToolStripItems cannot be invoked upon. So I have tried invoking their container, the MenuStrip, with the same function. I am still getting a threading/invoke problem where the thread stops running as soon as I try to access the ToolStripItem.
Here is the code I'm using to retrieve the Tag information after invoke:
void button_DragDrop(object sender, DragEventArgs e)
{
menuStrip.Invoke(new DragEventHandler(MyDragFunction), new object[] { sender, e });
}
void MyDragFunction(object sender, DragEventArgs e)
{
int id = (int)((ToolStripButton)sender).Tag;
// Debugging never reaches this line
int dragId = (int)e.Data.GetData(DataFormatName, false);
MoveItem(id, dragId);
}
Is Drag and Drop to a component like a ToolStripItem simply not possible? Or am I doing something wrong?

Here is the code I got to work for me.
I assign the DragDrop properties in the form constructor since they are hidden in the designer.
foreach (object o in menuStrip.Items)
{
if (o is ToolStripButton)
{
ToolStripItem item = (ToolStripItem)o;
item.AllowDrop = true;
item.DragEnter += new DragEventHandler(item_DragEnter);
item.DragOver += new DragEventHandler(item_DragOver);
item.DragDrop += new DragEventHandler(item_DragDrop);
}
}
private void item_DragEnter(object sender, DragEventArgs e)
{
if (e.Data.GetDataPresent(DataFormatName, false))
{
e.Effect = DragDropEffects.Move;
}
}
private void item_DragOver(object sender, DragEventArgs e)
{
if (e.Data.GetDataPresent(DataFormatName, false))
{
e.Effect = DragDropEffects.Move;
}
}
private void item_DragDrop(object sender, DragEventArgs e)
{
int id = (int)e.Data.GetData(DataFormatName, false);
int category = Convert.ToInt32((sender as ToolStripButton).Tag);
MyFunction(category, id);
}

Hanging controls properties on Application.Idle, good or bad?

I'm writing a simple application with several controls on a Windows form. I need to monitor the state of buttons (enabled/disabled) according to the state of a textbox and a listbox.
For example, when the listbox is empty, buttons Delete, Delete All and Edit are to be disabled, or when either the textbox or the listbox is empty button Forward is disabled, and so on.
So, I put the change of these properties on Application.Idle event, so it goes something like this:
private void MainForm_Load(object sender, EventArgs e)
{
Application.Idle += new EventHandler(Application_Idle);
}
public void Application_Idle(object sender, EventArgs e)
{
CheckFillingFields(forwardBtn);
CheckFillingList(deleteBtn);
CheckFillingList(deleteAllBtn);
CheckFillingList(editBtn);
}
private void CheckFillingFields(object sender)
{
if (questionTxt.Text == "" || answersLst.Items.Count == 0)
(sender as Button).Enabled = false;
else
(sender as Button).Enabled = true;
}
private void CheckFillingList(object sender)
{
if (answersLst.Items.Count == 0)
(sender as Button).Enabled = false;
else
(sender as Button).Enabled = true;
}
So, the question is - is it acceptable to use Application.Idle in this case? Or should I make these properties dependable on user actions? (For example, when the user deletes an item from the listbox, I should check if it was the last one, and disable the corresponding buttons.)
Thanks a lot in advance, I really appreciate your help!

The simple answer is that, yes, the idle checking is bad and you should re-check the state of your controls on their change events, not "whenever possible".

Is there a "All Children loaded" event in WPF

I am listening for the loaded event of a Page. That event fires first and then all the children fire their load event. I need an event that fires when ALL the children have loaded. Does that exist?

I hear you. I also am missing an out of the box solution in WPF for this.
Sometimes you want some code to be executed after all the child controls are loaded.
Put this in the constructor of the parent control
Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new Action(() => {code that should be executed after all children are loaded} ));
Helped me a few times till now.

Loaded is the event that fires after all children have been Initialized. There is no AfterLoad event as far as I know. If you can, move the children's logic to the Initialized event, and then Loaded will occur after they have all been initialized.
See MSDN - Object Lifetime Events.

You can also use the event: ContentRendered.
http://msdn.microsoft.com/en-us/library/ms748948.aspx#Window_Lifetime_Events

WPF cant provide that kind of an event since most of the time Data is determining whther to load a particular child to the VisualTree or not (for example UI elements inside a DataTemplate)
So if you can explain your scenario little more clearly we can find a solution specific to that.

One of the options (when content rendered):
this.LayoutUpdated += OnLayoutUpdated;
private void OnLayoutUpdated(object sender, EventArgs e)
{
if (!isInitialized && this.ActualWidth != 0 && this.ActualHeight != 0)
{
isInitialized = true;
// Logic here
}
};

Put inside your xaml component you want to wait for, a load event Loaded="MyControl_Loaded" like
<Grid Name="Main" Loaded="Grid_Loaded"...>
<TabControl Loaded="TabControl_Loaded"...>
<MyControl Loaded="MyControl_Loaded"...>
...
and in your code
bool isLoaded;
private void MyControl_Loaded(object sender, RoutedEventArgs e)
{
isLoaded = true;
}
Then, inside the Event triggers that have to do something but were triggering before having all components properly loaded, put if(!isLoaded) return; like
private void OnButtonChanged(object sender, RoutedEventArgs e)
{
if(!isLoaded) return;
... // code that must execute on trigger BUT after load
}

I ended up doing something along these lines.. your milage may vary.
void WaitForTheKids(Action OnLoaded)
{
// After your children have been added just wait for the Loaded
// event to fire for all of them, then call the OnLoaded delegate
foreach (ContentControl child in Canvas.Children)
{
child.Tag = OnLoaded; // Called after children have loaded
child.Loaded += new RoutedEventHandler(child_Loaded);
}
}
internal void child_Loaded(object sender, RoutedEventArgs e)
{
var cc = sender as ContentControl;
cc.Loaded -= new RoutedEventHandler(child_Loaded);
foreach (ContentControl ctl in Canvas.Children)
{
if (!ctl.IsLoaded)
{
return;
}
}
((Action)cc.Tag)();
}