Dynamic Queries Example

These instructions will build an example program that looks like this:

The form will automatically load 100 copies of the same picture varying in the size and border style.  You can perform a dynamic query with the filters on the left side of the window.  Dynamic queries provide continuous updating of results - the results are shown as you change the search criteria!

Download the code by clicking on the Zip file.

Instructions for Creating the Example:

1. Start Visual Studio from the Start menu.
2. Click on the New Project button in the bottom of the screen.
3. Select Visual Basic Projects, and Windows Application.  In the Name box give your project a name.
4. Layout your form like this:

The track bars are called trkWidth and trkHeight.  The checkboxes are called chkBorder and chkNoBorder.  The rectangle on the right is a panel called Panel1.  It will contain all of our pictureboxes, which will be loaded at runtime.

5. Declare an array of picture boxes with no size at the top of your code window:

' create an array of picture boxes
Dim pics() As PictureBox

6. Add the following code to a Form1_Load event to create each picture box and position it in the panel:

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Dim i As Integer
    ' resize our picture box to include 100 picture boxes
    ReDim pics(100)
    ' set the properties for each of our picture boxes
    For i = 0 To 99
        ' allocate memory for the picture box
        pics(i) = New PictureBox()
        With pics(i)
            'put the same picture in each picture box
            .Image = Image.FromFile("pic1.jpg")
            ' set it so the picture will resize depending on the size of the picture box
            .SizeMode = PictureBoxSizeMode.StretchImage
            ' pick a random size between 1 and 80 pixels wide and tall
            .Size = New Size(Int(80 * Rnd() + 1), Int(80 * Rnd() + 1))
            ' pick a random location with the panel
            .Location = New Point(Int(Panel1.Width * Rnd() + 1), Int(Panel1.Height * Rnd() + 1))
            ' store the index in the array
            .Tag = i

            ' choose to use a border or no border
            If Int(2 * Rnd() + 1) = 1 Then
                .BorderStyle = BorderStyle.Fixed3D
            Else
                .BorderStyle = BorderStyle.None
            End If

        End With
    Next

    ' add the picture boxes to the panel
    Me.Panel1.Controls.AddRange(pics)

    ' start with all the pictures visible
    chkBorder.Checked = True
    chkNoBorder.Checked = True
End Sub
 

7. Create a sub routine to handle the dynamic query.  Use the handles statement to link each of our search filter controls to the sub routine so that when the search criteria is changed the Query sub routine will fire.

Private Sub Query(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles trkWidth.Scroll, trkHeight.Scroll, chkBorder.CheckedChanged, chkNoBorder.CheckedChanged
    ' this subroutines handles all query controls - when each control is changed the query runs

    ' the dynamic query
    ' check all pictures to see if they match the search criteria
    Dim i As Integer
    For i = 0 To 99

        ' check the width and height, if the picture isn't bigger, go to the else
        If pics(i).Height > trkHeight.Value And pics(i).Width > trkWidth.Value Then

            ' check the border of the picture, if it doesn't match the checkboxes, go to the else
            If (chkBorder.Checked = True And pics(i).BorderStyle = BorderStyle.Fixed3D) Or _
            (chkNoBorder.Checked = True And pics(i).BorderStyle = BorderStyle.None) Then

                ' picture matches the critera, show it
                pics(i).Visible = True
            Else
                ' picture doesn't match criteria, hide it
                pics(i).Visible = False

            End If
        Else
            ' picture doesn't match criteria, hide it
            pics(i).Visible = False
        End If
    Next
End Sub