传递“不是新对象”作为参数

Question

Probably a simple one, I am just learning C#.

I am using VS2013, having two forms.

Goal: A textbox has a default value. At the time of a button (still on form1) is pressed, pass the new, entered value from the textbox on form1, from form1 to form2.

I have one textbox on Form1 and on Form2 a button, that is telling me what's in the textbox of Form1. This is all right, but I am handling TextChangedEvent so if I modify the text, the creation of a new object of Form1 will result in having a new instance, thus the changed text will be wiped out. It remains the default value.

Question: how to reference to the current value of the object, not create a new instance and have default values?

Form1:

public partial class Form1 : Form
{
    public string value { get; set; }

    public Form1()
    {
        Application.EnableVisualStyles();
        InitializeComponent();
        this.textBox1.Text = "Default";
    }

    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        value = this.textBox1.Text;
    }
    private void button1_Click(object sender, EventArgs e)
    {
        switch (comboBox2.SelectedIndex)
        {
            case -1:
                MessageBox.Show("You didn't choose anything.");
                break;
            case 0:
                MessageBox.Show("Value of variable: " + value); // Here it's the new value, NOT "Default"
                Form2 form_Form2 = new Form2();
                form_Form2.ShowDialog();
                break;
        }
    }
}

Form2:

public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
    }
    private void button1_Click(object sender, EventArgs e)
    {
        Form1 getdata = new Form1();
        string value = getdata.value;
        if (checkBox1.Checked)
        {
            MessageBox.Show("Value: " + value); // Here it's "Default" :(
        }
        else if (!checkBox1.Checked)
        {
            MessageBox.Show("Value: " + value); // TBD
        }
    }
}

Answer 1

The solution is to inject a reference to Form1 into Form2 . You could do this like:

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

    public Form1 OtherForm { get; set; }

    private void button1_Click(object sender, EventArgs e)
    {
        string value = OtherForm.value;
        ...

Then in the sction of code where you create the Form1 and Form2 instances, do something like:

Form1 form1 = new Form1();
Form2 form2 = new Form2();
form2.OtherForm = form1;

Answer 2

I would just create a variable on form 2 and a method that changes it, then when the button is pressed on form 1 do something like form_form2.someMethod(value)
but i'm not sure that's the recommended way to handle it.

you would also have to change the scope of form_form2 i believe.

Answer 3

Don't create a new Form1. Pass your Value to your Form2. I modified your code a little bit:

Form1 :

namespace GUITest
{
  public partial class Form1 : Form
  {
    private string _value = "Default"; // Create a private field with your Default Value

    public string Value
    {
      get
      {
        return _value;
      }
      set
      {
        _value = value
      }
    }

    public Form1()
    {
      Application.EnableVisualStyles();
      InitializeComponent();
      this.textBox1.Text = Value;
    }

    private void textBox1_TextChanged(object sender, EventArgs e)
    {
      Value = this.textBox1.Text;
    }

    private void button1_Click(object sender, EventArgs e)
    {
      switch (comboBox2.SelectedIndex)
      {
        case -1:
          MessageBox.Show("You didn't choose anything.");
          break;
        case 0:
          MessageBox.Show("Value of variable: " + value); // Here it's the new value, NOT "Default"
          Form2 form_Form2 = new Form2(Value); // Pass the Value to the Constructor of Form2
          form_Form2.ShowDialog();
          break;
      }
    }
  }
}

Form2

namespace GUITest
{
  public partial class Form2 : Form
  {

    private string _value; // Again your field but this time without your default Value

    public Form2(string myVal)
    {
      InitializeComponent();
      _value = myVal;
    }

    private void button1_Click(object sender, EventArgs e)
    {
      if (checkBox1.Checked)
      {
        MessageBox.Show("Value: " + _value); // Here it's now not anymore "Default" :)
      }
      else // Removed redundant if
      {
        MessageBox.Show("Value: " + _value); // TBD
      }
    }
  }
}

And something general: Even if it's only you who is working on this project... Give your controls self explaining names ;) It'll make your developer life much easier :)

Code should work. I couldn't test it at the moment. If errors occur then pls comment! :)

Source: My own know-how ^^

Answer 4

Since you're using ShowDialog() , simply grab the value off your Form2 instance when it returns execution back to Form1. Form2 does not need any kind of reference to Form1 for this to work...

So you need to do two things:

1. Somehow pass the current value to Form2 (via the Constructor is a common way and has already been shown).
2. Retrieve the new value off Form2 if "OK" was returned. A property in Form2 would be best.

Here are those two things put together:

public partial class Form1 : Form
{

    public Form1()
    {
        InitializeComponent();
        this.textBox1.Text = "Default";
    }

    private void button1_Click(object sender, EventArgs e)
    {
        switch (comboBox2.SelectedIndex)
        {
            case -1:
                MessageBox.Show("You didn't choose anything.");
                break;
            case 0:
                Form2 form_Form2 = new Form2(this.textBox1.Text);
                if (form_Form2.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                {
                    this.textBox1.Text = form_Form2.Value;
                }
                break;
        }
    }

}

public partial class Form2 : Form
{

    private Form2() { }

    public string Value
    {
        get
        {
            return this.textBox1.Text;
        }
    }

    public Form2(string currentValue)
    {
        InitializeComponent();
        this.textBox1.Text = currentValue;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        this.DialogResult = System.Windows.Forms.DialogResult.OK;
    }

}