我們知道 C# winform 跨窗體傳值，子父窗體交互一般用委托來實現。之前都是子窗體和父窗體兩級交互，如果子窗體再生一個子子窗體，然后子子窗體調用父窗體函數，這樣該如何操作？

我想到的實現方式還是用委托變量一級一級的往下傳。

下面是實現的效果：

▲ Form1 加載 Uc1，在 Uc1 下加載 Uc2，Uc2 下返回 Uc1

Form1.cs

using?System;
using?System.Collections.Generic;
using?System.ComponentModel;
using?System.Data;
using?System.Drawing;
using?System.Linq;
using?System.Text;
using?System.Threading.Tasks;
using?System.Windows.Forms;

namespace?WindowsFormsApp1
{
????public?partial?class?Form1?:?Form
????{
????????public?Form1()
????????{
????????????InitializeComponent();
????????????this.userControl1.LoadUserF2?=?this.LoadFrm;
????????????this.userControl1.action?=?()?=>?this.button1_Click(null,?null);
????????}

????????private?UserControl1?userControl1?=?new?UserControl1()?{?Dock?=?DockStyle.Fill};

????????private?void?button1_Click(object?sender,?EventArgs?e)
????????{
????????????this.LoadFrm(this.userControl1);
????????}

????????private?void?LoadFrm(Control?control)
????????{
????????????this.panel1.Controls.Clear();
????????????this.panel1.Controls.Add(control);
????????}
????}
}

UserControl1.cs

using?System;
using?System.Collections.Generic;
using?System.ComponentModel;
using?System.Drawing;
using?System.Data;
using?System.Linq;
using?System.Text;
using?System.Threading.Tasks;
using?System.Windows.Forms;

namespace?WindowsFormsApp1
{
????public?partial?class?UserControl1?:?UserControl
????{
????????public?UserControl1()
????????{
????????????InitializeComponent();
????????????//?this.userControl2.backUc1?=?this.action;?//?放這里，結果都是?null
????????????//?這個綁定不能放構造函數。因為構造函數執行的時候 action = null。
????????????//?主窗體先構造好子窗體，然后再給子窗體 action 賦值。
????????????//?所以，綁定要放在子窗體構造完畢之后。
????????}

????????private?UserControl2?userControl2?=?new?UserControl2()?{?Dock?=?DockStyle.Fill?};
????????public?Action?LoadUserF2;public?Action?action;private?void?button1_Click(object?sender,?EventArgs?e)
????????{this.LoadUserF2?.Invoke(this.userControl2);this.userControl2.backUc1?=?this.action; // 在這綁定
????????}
????}
}

UserControl2.cs

using?System;
using?System.Collections.Generic;
using?System.ComponentModel;
using?System.Drawing;
using?System.Data;
using?System.Linq;
using?System.Text;
using?System.Threading.Tasks;
using?System.Windows.Forms;

namespace?WindowsFormsApp1
{
????public?partial?class?UserControl2?:?UserControl
????{
????????public?UserControl2()
????????{
????????????InitializeComponent();
????????}

????????public?Action?backUc1;

????????private?void?button1_Click(object?sender,?EventArgs?e)
????????{
????????????backUc1?.Invoke();
????????}
????}
}

要注意的地方：

在 UserControl1.cs 中的注釋中說明。這里的委托綁定不能放在構造函數下，因為構造函數執行的時候 action = null。

主窗體先構造好子窗體，然后再給子窗體 action 賦值。所以，這里的綁定要放在子窗體構造完畢之后。

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