当在 C# .net 中单击第二个表单上的按钮时，如何从第二个中获取主表单中的字符串数据？

Question

一开始我以为这对我来说不会有问题，但现在我想不通了。所以， 当我在主窗体中单击 Button1 时，会打开 form2。 Form2 是简单的数字键盘，用户可以输入一些数据。在 form2 上也是保存。当用户点击它时，输入的值应该传递给主窗体，从那一刻起，主窗体中必须发生一些事件，其中包含来自 form2 的数据。你能给我一些例子或任何帮助吗？谢谢！

 // code from main form to create form2
 private void button1_Click(object sender, EventArgs e)
    {
        // Create a new instance of the Form2 class
        Form2 settingsForm = new Form2();

        // Show the settings form
        settingsForm.Show();

        string val = settingsForm.ReturnValue1;            

        MessageBox.Show(val);
    }

//button save on form2
private void button13_Click(object sender, EventArgs e)
    {
        this.ReturnValue1 = "Something";
        this.ReturnValue2 = DateTime.Now.ToString(); //example
        this.Close();
        //after this, some event should happen in main form !
    }

Answer 1

有很多解决方案可以做你想做的事；但我认为其中之一将解决您的问题。

1-简单易行：在Form2中使用公共属性，buttonSave被点击时初始化，Form1中访问：

Form2：

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

    private void button1_Click(object sender, EventArgs e){
        YourDate = "something";
        Close();
    }

    public object YourDate { get; private set; }
}

Form1：

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

    private void button1_Click(object sender, EventArgs e){
        var f2 = new Form2();
        f2.ShowDialog();
        var data = f2.YourDate;
    }
}

2- 更好的方法是使用更灵活、更专业的编程友好的事件：

Form2：

public partial class Form2 : Form {

    public Form2() {
        InitializeComponent();
    }

    // create an event of Action<T> which T is your data-type. e.g. in this example I use an object. 
    public event Action<object> SaveClicked;

    // create an event invocator, to invoke event whenever you want
    protected virtual void OnSaveClicked(object data){
        var handler = SaveClicked;
        if (handler != null)
            handler(data);
    }

    private void button1_Click(object sender, EventArgs e){
        // prepare your data here, -object, or string, or int, or whatever it is
        var data = PrepareYourDataHere;
        // invoke the event
        OnSaveClicked(data);
        Close();
    }
}

Form1：

public partial class Form1 : Form {

    public Form1() {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e){
        // create an instance of Form2
        var f2 = new Form2();
        // add an event listener to SaveClicked event -which we have declared it in Form2
        f2.SaveClicked += f2_SaveClicked;
        f2.Show();
        // or: f2.ShowDialog();
    }

    void f2_SaveClicked(object obj) {
        // get data and use it here...
        // any data which you pass in Form2.OnSaveClicked method, will be accessible here
    }
}

更新：

如果你想在form1中触发一些事件，在form2关闭之后，你可以简单地给Form2.FormClosed事件添加一个监听器：

// code from main form to create form2
private void button1_Click(object sender, EventArgs e) {
    // Create a new instance of the Form2 class
    Form2 settingsForm = new Form2();
    settingsForm.FormClosed += SettingFormClosed;

    // Show the settings form
    settingsForm.Show();

    string val = settingsForm.ReturnValue1;            

    MessageBox.Show(val);
}

void SettingFormClosed(object sender, FormClosedEventArgs e) {
    // this method will be called automatically when form2 closed
}

Answer 2

这里有一个示例如何实现这一目标

//这里我假设form1是mainform

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

        public void UpdateMainForm(string updatedString)
        {
            //here you can update  and invoke methods
             //Once called you could raise events in your mainform 


        }

        private void button1_Click(object sender, EventArgs e)
        {
            using (Form2 form2 = new Form2(this))
            {
                form2.ShowDialog();

            }
        }

    }

Form2

public partial class Form2 : Form
    {
        private Form1 _mainForm1; 
        public Form2(Form1  mainForm1)
        {
            InitializeComponent();
            _mainForm1 = mainForm1; 
        }


        private void button1_Click(object sender, EventArgs e)
        {
            _mainForm1.UpdateMainForm( DateTime.Now.ToString());
        }
    }