I am working on a C# piano. I have already built the music keyboard and the staff. Everytime a user presses a key, it is displayed on the staff in its relevant position.
The music note displayed on the staff is stored in an array of pictureboxes, as shown below.
public void addPictureBox(int x, int y, Image image)
{
picBox[cnt] = new PictureBox();
picBox[cnt].Image = image;
picBox[cnt].Location = new Point(x, y);
picBox[cnt].BackColor = Color.Transparent;
panel3.Controls.Add(picBox[cnt]);
picBox[cnt].BringToFront();
picBox[cnt].MouseDown += new MouseEventHandler(Pic_MouseDown);
picBox[cnt].MouseUp += new MouseEventHandler(Pic_MouseUp);
cnt++;
}
The Pic_MouseDown and Pic_MouseUp events allow the user to play the note by clicking on it from the staff.
What I want to do now is to create an event on picBox[cnt] for dragging. However, picBox[cnt].MouseDown and picBox[cnt].MouseUp have already been registered to Pic_MouseDown and Pic_MouseUp event handlers.
How can I do an event to handle dragging since MouseDown and MouseUp have already been registered to other event handlers?
Thanks :)
The great thing about event handlers is that you can have as many attached handlers as you want. The += (operator overload) means you are attaching a new event handler to the existing handlers. You can add as many event handlers as you desire.
Event Handler Overview
If you create a isDragging boolean instance field, which you set to true in the mouse down and false in mouse up, then you can use the mouse move event to detect whether the object should be moved or not.
You'll need to use a combination of MouseDown, MouseMove and MouseUp events. In MouseDown, you do little more than set a flag to indicate that the mouse was pressed, and record where it was pressed. In MouseMove, you check to see if the button is still down and the cursor has moved further than SystemInformation.DragSize, which indicates that the user is dragging rather than clicking, and start the drag operation if needed. In MouseUp, you either complete the drag or perform the click action.
I believe the conventional wisdom for Drag-n-drop is
Call DoDragDrop in the (source control's) MouseDown handler
set AllowDrop = true in the targe control's AllowDrop property
There's a whole series of drag events to fine tune behavior
One does not seem to have to worry about any latent MouseUp or MouseClick events. I'm assuming this is because the physical actions of button press and release are done over different controls and/or the mouse physically moved "far enough".
Related
I have created a Windows Forms application, but I get strange behaviour from the Capture property of a control.
On a blank form, with a single label called "label1" and the code
public Form1()
{
InitializeComponent();
label1.MouseDown += pictureBox1_MouseDown;
}
void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{
Debug.WriteLine(label1.Capture);
label1.Capture = !label1.Capture;
Debug.WriteLine(label1.Capture);
}
I observed, that the first WriteLine always says "True", the second one always says "False" when the button is clicked. Even when clicked multiple times.
The label never reacts to clicks outside its border, not even when I use label1.Capture = true instead.
Am I misunderstanding the expected behaviour of the "Capture" property? I expected the initial value to be false, and the label not to react to clicks outside, after the first click I expect the value to be true, and the label to react to all mouse clicks, even outside its borders.
In a MouseDown event, the Capture for the control always set to true initially. So normally if you perform a MouseDown and then without releasing mouse button move your mouse out of the control and then release mouse button, the MouseUp event of the control will be fired.
If you set Capture to false in MouseDown, then the mouse up event of your control will only fire if your mouse is over the control and if you move the mouse out of your control and then release mouse button, the MouseUp event of your control will not raise.
Also in MouseUp the capture will be released automatically.
For more information take a look at these resources:
WmMouseDown method source code
WmMouseUp method source code
CaptureInternal proprty source code
SetCapture documentations
ReleaseCapture documentations
I'm having some troubles getting DragDrop.DoDragDrop to work along nicely with a left click event.
My control has several links which can either be dragged around or left clicked to visit.
I currently subscribe to the preview mouse move event which is where i launch the drag and drop event if the left mouse button is pressed.
In another call back i handle the mouse left button down and up event to check for a click. Is there anyway to check if DragDrop actually had a drag drop event take place?
See this link drag drop in wpf explained end to end and scroll down a little to the section "Detecting Drag & Drop"
Code inserted here encase the blog goes missing...
From [http://msdn2.microsoft.com/en-us/library/aa289508(vs.71).aspx] Here is the sequence of events in a typical drag-and-drop operation:
Dragging is initiated by calling the DoDragDrop method for the source control.
The DoDragDrop method takes two parameters:
data, specifying the data to pass allowedEffects, specifying which operations (copying and/or moving) are allowed
A new DataObject object is automatically created.
This in turn raises the GiveFeedback event. In most cases you do not need to worry about the GiveFeedback event, but if you wanted to display a custom mouse pointer during the drag, this is where you would add your code.
Any control with its AllowDrop property set to True is a potential drop target. The AllowDrop property can be set in the Properties window at design time, or programmatically in the Form_Load event.
As the mouse passes over each control, the DragEnter event for that control is raised. The GetDataPresent method is used to make sure that the format of the data is appropriate to the target control, and the Effect property is used to display the appropriate mouse pointer.
If the user releases the mouse button over a valid drop target, the DragDrop event is raised. Code in the DragDrop event handler extracts the data from the DataObject object and displays it in the target control.
Detecting Drag & Drop
Before the DoDragDrop is called, we must detect a mouse Drag operation on the source... A mouse drag is usually a MouseLeftButtonDown + a MouseMove (before MouseLeftButton goes up).
So, our drag & drop source control needs to subscribe to these two events:
void Window1_Loaded(object sender, RoutedEventArgs e)
{
this.DragSource.PreviewMouseLeftButtonDown += new MouseButtonEventHandler(DragSource_PreviewMouseLeftButtonDown);
this.DragSource.PreviewMouseMove += new MouseEventHandler(DragSource_PreviewMouseMove);
}
To prevent from starting a false drag & drop operation where the user accidentally drags, you can use
SystemParameters.MinimumHorizontalDragDistance and SystemParameters.MinimumVerticalDragDistance
One way to do this is on MouseLeftButtonDown, record the starting position and onMouseMove check if the mouse has moved far enough..
void DragSource_PreviewMouseMove(object sender, MouseEventArgs e)
{
if (e.LeftButton == MouseButtonState.Pressed && !IsDragging)
{
Point position = e.GetPosition(null);
if (Math.Abs(position.X - _startPoint.X) > SystemParameters.MinimumHorizontalDragDistance ||
Math.Abs(position.Y - _startPoint.Y) > SystemParameters.MinimumVerticalDragDistance)
{
StartDrag(e);
}
}
}
void DragSource_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
_startPoint = e.GetPosition(null);
}
Its a Drag .. now what?
The data! You need to find out what is under the mouse when dragging.
I will omit take the easy way out and assume that whoever is triggering the MouseMove is what I want to drag .. so look at MouseEventArgs.OriginalSource.. [or you could do some 2D HitTesting using VisualTreeHelper .. In Part3 of this write up will try to walk you through hit testing the listbox -which is the other common scenario I encounter-.
Once you have the object to drag, you will need to package what you are a sending into a DataObject that describes the data you are passing around.
DataObject is a wrapper to push generic data (identified with extensible formats) into drag/drop.. As long as both the source and destination understand the format, you will be set. As such, DataObject has a couple interesting methods:
SetData ( Type format, object data ) /// format is the "format" of the day you are passing ( e.g. Formats.Text, Formats.Image, etc.. ) you can pass any custom types.
GetDataPresent ( Type format ) /// is what the drop target will use to inquire and extract the data .. if it is a type it can handle, it will call GetData () and handle it ..
Not much interesting stuff here.. In the sample I just hard-coded my data to be of type string... this makes it easier to paste into external containers (for example Word, which you can use to test this part of the write-up). I do have to stress that drag & dropping should be about the data ...
Providing visual feedback during the drag & drop operation..
Before we call DoDragDrop () we have a few 'choices' to make around the feedback we want to provide and the 'scope' of the d&d.
Do we want a custom cursor to display while we are doing the Drag operation ? If we want a cursor, what should it be?
How far do we want to drag? within the app or across windows apps?
Simplest scenario: No custom cursor and we want it to drag across apps:
If you don't want a fancy cursor, you are done!! You can call DoDragDrop directly ...
private void StartDrag(MouseEventArgs e)
{
IsDragging = true;
DataObject data = new DataObject(System.Windows.DataFormats.Text.ToString(), "abcd");
DragDropEffects de = DragDrop.DoDragDrop(this.DragSource, data, DragDropEffects.Move);
IsDragging = false;
}
Note: this code allows you to drag & drop across processes, it uses the default operating system feedback ( e.g. + for copy)..
there are Drag Over/ Enter / Leave Attached events
you can subscribe methods to these (or one) events on your dragged UIElement and see if the Dragging occurs .
I'm having a problem with release a captured mouse. My application demand that I make a sequence of actions (means that they will run automatically one after another). The sequences are:
_ Select an object
_ Enter a value on a message box for the object to rotate according to the entered value.
At run time: I click on the object, it activate the MouseLeftButtonDown event of the selected object. Then the message box appears. This message box blocks my mouse to activate MouseLeftButtonUp event of that object. So I have to click the object one more time to activate the MouseLeftButtonUp event or my application cannot continue running.
Can anyone helps me with this?
That's why a lot of controls only take action on the MouseUp event. They use the MouseDown event to do something like indicating state or selection. And use mouse capture (Capture property in Winforms) to ensure that they'll get the MouseUp event even if the mouse is moved outside of the window. Try it in your browser right now, press and hold the right mouse button, nothing happens, let it go. Exact same behavior when you left-click a link or button.
Sounds like that's what you want to do as well.
I have a Canvas which is present in a UserControl, I have attached the DoubleClick event to this UserControl like this
mainWindow.CanvasLayout.MouseDoubleClick +=
new MouseButtonEventHandler(CanvasLayout_MouseDoubleClick);
I am using this event handler to achieve full screen functionality.
Now, Canvas can have various controls placed inside it. Drag and drop functionality is implemented for these controls similar to this codeproject article.
Basically, I handle these events for a control -
this._dragSource.PreviewMouseLeftButtonDown +=
new MouseButtonEventHandler(DragSource_PreviewMouseLeftButtonDown);
this._dragSource.PreviewMouseMove +=
new System.Windows.Input.MouseEventHandler(DragSource_PreviewMouseMove);
this._dragSource.PreviewMouseLeftButtonUp +=
new MouseButtonEventHandler(DragSource_PreviewMouseLeftButtonUp);
Now, when user DoubleClicks on a control(present in canvas) both DoubleClick(Full Screen) and single Click(drag & drop) operations are performed, i.e. if user double clicks on control and change its mouse position quickly, control position is changed(its dragged and dropped to new position).
Is there any way I can prevent drag and drop operation when user double clicks on a control?
Got it, Instead of handling MouseDoubleClick event, I used PreviewMouseLeftButtonDown -
mainWindow.CanvasLayout.PreviewMouseLeftButtonDown
+= new MouseButtonEventHandler(CanvasLayout_PreviewMouseLeftButtonDown);
and
void CanvasLayout_PreviewMouseLeftButtonDown(object s, MouseButtonEventArgs e)
{
if (e.ClickCount > 1)
{
// Do double-click code
// Code for FullScreen
e.Handled = true;
}
}
What you need to do is, on mouse up start a timer the time should be retrieved from SystemInformation.DoubleClickTime, and do the click action on the timer tick (only if you didn't detect the double click in the mean time, obviously).
Likewise use SystemInformation.DragSize to prevent accidental drag&drop.
Note, the SystemInformation class is part of WinForms so you need to add a reference to System.Windows.Forms, this class will work just fine in WPF apps.
I'm making a custom control with a panel. I want to be able to drag and drop it so I've implemented that in the MouseDown event of my control. But I want the thing to react when you start drag to give a little feedback to the user. So in the MouseDown even I change the color. Then I want to change it back in the MouseUp event.
My control is not installed into VS2008 but just a class I've written that I instanciate at run time (I don't know in advance how many I need and so on). Now, my control exposes a MouseDown event so as to be able to be dragged. When I subscribe to this event from the parent application to actually perform the drag and drop my control is not repainted on its MouseUp event! In fact, the MouseUp is never invoked. If, on the other hand, I don't subscribe to the event in the parent app it works as intended.
What's going on? Is the parent interrupting the flow so that the MouseUp event never fires in my control? How do I get around this?
I'm not sure if you are using Windows Forms or WPF, but in Windows forms here is what I mean:
public class DerivedPanel : Panel
{
protected override void OnMouseDown(MouseEventArgs e)
{
base.OnMouseDown(e);
Capture = true;
}
protected override void OnMouseUp(MouseEventArgs e)
{
base.OnMouseUp(e);
Capture = false;
// Change your color or whatever here
}
}
In WPF there are two methods, CaptureMouse() and ReleaseMouseCapture() to do the same thing. When the control captures the mouse, it will received mouse events even if the cursor isn't over the control. This could be causing your problem. See MSDN Article
Do you capture the mouse in the custom control on the mousedown event? Try capturing on the mousedown and releasing the capture on the mouseup.