Winform中按钮的Click事件反复触发List中的值数

Question

I have a windows form (parent) that takes a value from textbox and then opens child form which then uses that value to select an image from a directory. When multiple images are found for the particular value, I have the form modified to display a couple of buttons to navigate (Next & Previous) to display the different images. Upon first opening the parent form, entering a value and then using form.show() to display the child form – everything works as expected. But if another value is entered into parent form (child form can still be open or exited (hidden)) and the 'Next' button is clicked the code in the click event is running over again for however many number of images are in the List(imagesFound). Say I have 3 images in the List(imagesFound) and I step through the code in debug mode the btnNext click event fires 3 times in a row. This of course runs GetMultiImages method which causes sequence of displaying the images to be all of. And again, this doesn't happen the first time a value is entered into parent form. I've made sure the list and other variables are cleared out in GetImage method. I'm stumped…any ideas?

Form1:

public partial class Form1 : Form
{
    private string parcelID;
    Form2 viewer = new Form2();
    public Form1()
    {
        InitializeComponent();
    }
    private void button1_Click(object sender, EventArgs e)
    {
        parcelID = txtParID.Text;
        ShowViewer();
    }
    private void ShowViewer()
    {
        viewer.GetImage(parcelID);
        if (viewer.NoImageFound == true)
        {
            viewer.Show();
            viewer.Focus();     
        }
        else if (viewer.NoImageFound == false)
        {
            viewer.Hide();      
        }                             
    }
}

Child Form:

public partial class Form2 : Form
{
    public Button btnNext = new Button();
    public Button btnPrev = new Button();
    private List<string> imagesFound = new List<string>();
    private string Path;
    private string parcel;
    private int increment;
    private int maxNum;
    public bool NoImageFound;

    //multi image members
    private string firstMultiItem;
    private string selectMultiImage;
    Image parMultiImage;

    public Form2()
    {
        InitializeComponent();
    }

    public void GetImage(string ParcelID)
    {
        NoImageFound = true;
        parcel = ParcelID;
        increment = 0;
        maxNum = 0;
        firstMultiItem = null;
        selectMultiImage = null;
        parMultiImage = null;
        imagesFound.Clear();
        Path = "........\\Images\\";
        try
        {
            if (!string.IsNullOrEmpty(parcel))
            {
                string parcelTrim = parcel.Substring(0, 6);
                Path = Path + parcelTrim + "\\";
                foreach (string s in Directory.GetFiles(Path, parcel + "_" + "*"))
                {
                    string trimString = s.Replace(Path, "");
                    imagesFound.Add(trimString);
                }
                if ((imagesFound.Count == 0))
                {
                    MessageBox.Show("No images found for ParcelID: " + parcel);
                    picBox.Image = null;
                    this.Text = "";
                    NoImageFound = false;

                }
                else
                {
                    if (imagesFound.Count == 1)
                    {
                        string firstItem = imagesFound[0].ToString();
                        string selectImage = Path + firstItem;
                        Image parImage = Image.FromFile(selectImage);
                        //in order to access the picture box control you have to change it's 
                        //access modifier (Modifier) from private to public. Defaults to private
                        picBox.Image = parImage;
                        picBox.SizeMode = PictureBoxSizeMode.StretchImage;
                        this.Text = parcel;
                        SingleForm();
                    }
                    else if (imagesFound.Count > 1)
                    {
                        firstMultiItem = imagesFound[0].ToString();
                        maxNum = imagesFound.Count;
                        selectMultiImage = Path + firstMultiItem;
                        parMultiImage = Image.FromFile(selectMultiImage);
                        picBox.Image = parMultiImage;
                        picBox.SizeMode = PictureBoxSizeMode.StretchImage;
                        this.Text = parcel;
                        MultiImageForm();

                    }
                }
            }
            else
            {
                MessageBox.Show("No ParcelID");
            }
        }
        catch (DirectoryNotFoundException)
        {
            string text = parcel;
            MessageBox.Show("ParcelID: " + text + " could not be found.  The directory may be missing.", "There's a problem locating the image.",
                MessageBoxButtons.OK, MessageBoxIcon.Warning);
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

    private void SingleForm()
    {
        this.Height = 400;
        btnNext.Visible = false;
        btnPrev.Visible = false;
    }

    private void MultiImageForm()
    {
        //set form properties
        this.Text = parcel;
        this.Height = 432;
        //set btnNext properties
        btnNext.Location = new Point(307, 375);
        btnNext.Size = new Size(75, 25);
        btnNext.Font = new Font("Maiandra GD", 10, FontStyle.Bold);
        btnNext.Text = ">>";
        //add btnNext to form
        this.Controls.Add(btnNext);
        btnNext.Visible = true;
        btnNext.Enabled = true;
        //creating event handler for btnNext
        btnNext.Click += new EventHandler(btnNext_Click);
        //set btnPrev properties
        btnPrev.Location = new Point(12, 375);
        btnPrev.Size = new Size(75, 25);
        btnPrev.Font = new Font("Maiandra GD", 10, FontStyle.Bold);
        btnPrev.Text = "<<";
        //add btnPrev to form
        this.Controls.Add(btnPrev);
        btnPrev.Visible = true;
        btnPrev.Enabled = false;
        //creating event handler for btnPrev
        btnPrev.Click += new EventHandler(btnPrev_Click);

    }

    private void GetMultiImages()
    {
        try
        {
            firstMultiItem = imagesFound[increment].ToString(); 
            selectMultiImage = Path + firstMultiItem;
            parMultiImage = Image.FromFile(selectMultiImage);
            picBox.Image = parMultiImage;
            picBox.SizeMode = PictureBoxSizeMode.StretchImage;
        }
        catch (IndexOutOfRangeException)
        {
            MessageBox.Show("Index was out of range.");
        }
    }

    private void btnNext_Click(object sender, System.EventArgs e)
    {
        if (increment != maxNum - 1)
        {
            increment++;
            GetMultiImages();
        }
        EnableButtons();
    }

    private void btnPrev_Click(object sender, System.EventArgs e)
    {
        if (increment > 0)
        {
            increment--;
            GetMultiImages();
        }
        EnableButtons();
    }

    private void EnableButtons()
    {
        if (increment == 0)
        {
            btnPrev.Enabled = false;
            btnNext.Enabled = true;
        }
        else if (increment > 0 & increment != maxNum - 1)
        {
            btnPrev.Enabled = true;
            btnNext.Enabled = true;
        }
        else if (increment == maxNum - 1)
        {
            btnPrev.Enabled = true;
            btnNext.Enabled = false;
        }
    }

    private void Form2_FormClosing(object sender, FormClosingEventArgs e)
    {
        //overriding closing event
        this.Hide();
        e.Cancel = true;
    }
}

Answer 1

    //creating event handler for btnNext
    btnNext.Click += new EventHandler(btnNext_Click);

That's a bug. You keep adding a Click event handler for the button, each time you call MultiImageForm(). So the event handler runs multiple times for a single click.

Only add event handlers in the form constructor so you can be sure it is only done once.