C# object of class in different windows form

Question

If I run my project I get this window:

Then I press the button auto hinzufügen == add car . Here the code of the method:

private void button1_Click(object sender, EventArgs e)
{
    addCarcs window = new addCarcs();
    window.Show();
}

Now the second window opens:

I fill both fields and press the button auto hinzufügen == add car . Then I create a new object of the class car . Here the code:

private void button1_Click(object sender, EventArgs e)
{
    if((kennzeichen.Text != "") && (automarke.Text != ""))
    {
        car myCar = new car();
        myCar.addCar(kennzeichen.Text, automarke.Text);
        this.Close();
    }
}

Here is the code of the class car :

class car
{

    public car()
    {
        this.carMark = "";
        this.carMark = "";
    }

    public void addCar(string carMark, string carBrand)
    {
        this.carMark = carMark;
        this.carBrand = carBrand;
        carNumber++;
    }

    public string showCar()
    {
        return string.Format(
            "Automarke: {0} --- Autokennzeichen {1}", this.carBrand, this.carMark);
    }

    private string carMark;
    private string carBrand;
    static int carNumber; 
}

Now I come to the main Window again:

Now I press the second button auto anzeigen == show car . I want to show the added car, but if I write this code in the button method:

private void showCar_Click(object sender, EventArgs e)
{
    myCar.showCar();
}

I get an error:

How can I send the created object's of a class between different forms?

Answer 1

You need to create a Property Car MyCar { get;set; }' at the class level. Set its value in the constructor like Car MyCar { get;set; }' at the class level. Set its value in the constructor like Car MyCar { get;set; }' at the class level. Set its value in the constructor like MyCar = new Car() and access the MyCar` everywhere you need the Car object.

Answer 2

You should create a member car in the class that "creates" both windows, so both forms you open "recognize" the member car, and can access its data.

You can find more info here: https://msdn.microsoft.com/en-us/library/ms173121.aspx

and here: https://msdn.microsoft.com/en-us/library/ba0a1yw2.aspx

Answer 3

Well, you need to do the following:

Add a property called addedCar to your addCarcs Class:

public class addCarcs : Form
{
    public car addedCar { set; get; }
}

Add a property Called latestAddedCar to your Form1 Class:

public class Form1 : Form
{
    public car latestAddedCar { set; get; }
}

Change you addition logic to a ShowDialog :

private void button1_Click(object sender, EventArgs e)
{
    addCarcs window = new addCarcs();
    DialogResult dResult = window.ShowDialog();

    if (dResult == System.Windows.Forms.DialogResult.OK)
    {
        latestAddedCar = window.addedCar;
    }
}

Change your Data Entry Submission Logic to:

private void button2_Click(object sender, EventArgs e)
{
    if ((kennzeichen.Text != "") && (automarke.Text != ""))
    {
        car myCar = new car();
        myCar.addCar(kennzeichen.Text, automarke.Text);
        this.DialogResult = System.Windows.Forms.DialogResult.OK;
    }
}

Finally, access the newly added Attribute from the Main class Form1 :

private void showCar_Click(object sender, EventArgs e)
{
    if(latestAddedCar != null)
        latestAddedCar.showCar();
}