从另一种形式调用ComboBox

Question

I have 2 forms - Form1 and Form2, Form1 have ComboBox, Form2 property has FormBorderStyle as FixedToolWindow. I need to call ComboBox from Form2, how do I?

Answer 1

I see the that the question has been reworded and the meaning has changed significantly.

The simple fact is that Form2 shouldn't even know that the ComboBox exists or even that Form1 exists for that matter. The proper way to do this is for Form2 to raise an event and for Form1 to handle that event. When something needs to happen, Form2 raises the event and then Form1 accesses its own ComboBox.

Check this out . Part 3 explains how it SHOULD be done.

Here's a relatively contrived example:

Form1:

using System;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private Form2 form2Instance;

        private void button1_Click(object sender, EventArgs e)
        {
            // Check whether there is already a Form2 instance open.
            if (this.form2Instance == null || this.form2Instance.IsDisposed)
            {
                // Create a new Form2 instance and handle the appropriate event.
                this.form2Instance = new Form2();
                this.form2Instance.SelectedValueChanged += form2Instance_SelectedValueChanged;
            }

            // Make sure the Form2 instance is displayed and active.
            this.form2Instance.Show();
            this.form2Instance.Activate();
        }

        private void form2Instance_SelectedValueChanged(object sender, EventArgs e)
        {
            // Update the ComboBox based on the selection in Form2.
            this.comboBox1.SelectedIndex = this.form2Instance.SelectedValue;
        }
    }
}

Form2:

using System;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }

        /// <summary>
        /// Gets the value selected in the NumericUpDown as an int.
        /// </summary>
        public int SelectedValue { get { return Convert.ToInt32(this.numericUpDown1.Value); } }

        /// <summary>
        /// Raised when the value in the NumericUpDown changes.
        /// </summary>
        public event EventHandler SelectedValueChanged;

        private void numericUpDown1_ValueChanged(object sender, EventArgs e)
        {
            if (this.SelectedValueChanged != null)
            {
                // Notify any listeners that the selection has changed.
                this.SelectedValueChanged(this, EventArgs.Empty);
            }
        }
    }
}

As you can see, Form2 has no reference to Form1 at all so doesn't need to know or care whether Form1 exists.