放大ComboBox无法正常工作

Question

I have an application that scans an image to display on the application. After the image is scanned, I have the option to zoom the image. There's a combo box on the application that display the zoom percentage as well.

I can zoom fine using my mouse wheel and the combo box % changes accordingly which is fine. The problem happens if I manually select the combo box and select a zoom percentage, say 50%, then there's no changes at all.

Code:

private void ImageBox_ZoomLevelsChanged(object sender, EventArgs e)
{
    this.FillZoomLevels();
}

private void ZoomComboBox_Click(object sender, EventArgs e)
{

}

private void FillZoomLevels()
{
    ZoomComboBox.Items.Clear();

    foreach (int zoom in ImageBox.ZoomLevels)
        ZoomComboBox.Items.Add(string.Format("{0}%", zoom));
}

Am I doing anything wrong? Appreciate any help.

Answer 1

When there is more than one control on the Panel , and the ScrollBars are shown, the MouseWheel event of the Panel would be raised, but if there's only a PictureBox on the Panel whose Image large enough to make the panel's ScrollBars visible, then the MouseWheel event of the Panel won't be raised, instead, the Form's MouseWheel event fires.

In the following sample, I just add a PictureBox onto the Panel without any other controls added, set a large Image to the PictureBox which make the Panel 's ScrollBars invisible, since there's only one control on the panel, the MouseWheel event of the Panel won't be raised, but the Form's MouseWheel event be raised, we handle this event instead, handle the Form's KeyDown and KeyUp events as well.

Furthermore, set the SizeMode of the PictureBox to StretchImage instead of AutoSize , thus when we change the size of the PictureBox , the Image in the PictureBox will resize to fit the PictureBox .

The PictureBox.Scale() method won't help you in this screnario, change the size of the PictureBox instead.

public partial class Form4 : Form
{
    public Form4()
    {
        InitializeComponent();
    }

    bool ctrlKeyDown;
    bool shiftKeyDown;

    private void Form4_Load(object sender, EventArgs e)
    {
        this.ctrlKeyDown = false;
        this.shiftKeyDown = false;

        //If there's only PictureBox control on the panel, the MouseWheel event of the form raised
        //instead of the MouseWheel event of the Panel.
        this.MouseWheel += new MouseEventHandler(Form4_MouseWheel);
        this.KeyDown += new KeyEventHandler(Form4_KeyDown);
        this.KeyUp += new KeyEventHandler(Form4_KeyUp);

        //this is important for zooming the image
        this.pictureBox2.SizeMode = PictureBoxSizeMode.StretchImage;
    }

    void Form4_KeyUp(object sender, KeyEventArgs e)
    {
        this.ctrlKeyDown = e.Control;
        this.shiftKeyDown = e.Shift;
    }

    void Form4_KeyDown(object sender, KeyEventArgs e)
    {
        this.ctrlKeyDown = e.Control;
        this.shiftKeyDown = e.Shift;
    }

    void Form4_MouseWheel(object sender, MouseEventArgs e)
    {
        bool IsGoUp = e.Delta > 0 ? true : false;

        if (this.ctrlKeyDown)
        {
            if (IsGoUp && this.panel1.HorizontalScroll.Value > 5)
            {
                this.panel1.HorizontalScroll.Value -= 5;
            }

            if (!IsGoUp && this.panel1.HorizontalScroll.Value < this.panel1.HorizontalScroll.Maximum - 5)
            {
                this.panel1.HorizontalScroll.Value += 5;
            }
        }
        else if (this.shiftKeyDown)
        {
            int hStep = (int)(this.pictureBox2.Image.Width * 0.02);
            int vStep = (int)(this.pictureBox2.Image.Height * 0.02);
            if (IsGoUp)
            {
                this.pictureBox2.Width += hStep;
                this.pictureBox2.Height += vStep;
            }
            else
            {
                this.pictureBox2.Width -= hStep;
                this.pictureBox2.Height -= vStep;
            }
        }
        else
        {
            if (IsGoUp && this.panel1.VerticalScroll.Value > 5)
            {
                this.panel1.VerticalScroll.Value -= 5;
            }

            if (!IsGoUp && this.panel1.VerticalScroll.Value < this.panel1.VerticalScroll.Maximum - 5)
            {
                this.panel1.VerticalScroll.Value += 5;
            }
        }
    }
}