C# Event-Handling

Question

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 :)

When is this project due? Kinda looking forward to the end of the piano questions from you and your class mates. — Hans Passant
– Hans Passant, Commented Dec 30, 2011 at 16:31

SliverNinja · Accepted Answer · 2011-12-30 16:25:29Z

3

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

edited Dec 30, 2011 at 16:25

answered Dec 30, 2011 at 16:19

SliverNinja

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2 Comments

Clayton Over a year ago

How will the program know which event handlers to execute on a picBox[cnt].MouseDown event if there are multiple event handlers please? Thank you

SliverNinja Over a year ago

@Clayton - read the event handler overview for more details on how eventing works (pub/sub design pattern)

Espen Burud · Accepted Answer · 2011-12-30 16:24:52Z

2

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.

answered Dec 30, 2011 at 16:24

Espen Burud

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Comments

anton.burger · Accepted Answer · 2011-12-30 16:26:35Z

1

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.

answered Dec 30, 2011 at 16:26

anton.burger

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Comments

radarbob · Accepted Answer · 2011-12-30 18:04:52Z

0

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".

answered Dec 30, 2011 at 18:04

radarbob

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