我有一个Windows Forms App，它以我不了解的方式运行。我创建了一个简单的应用程序，以简化功能，以最小的逻辑再现功能。它有两种形式。
Form1： 有一个button1，单击该按钮时会将行添加到数据表中。 有一个button2，它显示一个表单并将数据表发送到该表单。
Form2： Form2从数据表创建一个数据视图，并将该数据视图绑定到列表框。 Form2也有一个button1，它在表单上执行this.Close（）。我读到任何用formName.Show（）打开的东西都将在.Close期间处理。
在这里，事情变得很奇怪。每次都可以单击Form1 button1以清除数据表并再次添加行。单击from1 button2之后，将显示form2，然后将其关闭，然后返回到form1，然后单击button1会引发错误。错误是来自form2（已关闭）listBox1_SelectedIndexChanged事件。
问题是，为什么要为已消失的窗体上已消失的控件触发事件？ 我已经找到了几种避免这种情况的方法，但是我想了解为什么会发生这种情况，例如将listbox设置为datasource = null，但想知道发生了什么。。花了半天时间试图弄清楚这一点。这样的社区，请在这里教育我。
Form1代码
public partial class Form1 : Form
{
Boolean bInitialLoad = true;
DataTable dtHardware = new DataTable("Hardware");
Form2 multiServerView = new Form2();
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
dtHardware.Clear();
if (bInitialLoad == true)
{
dtHardware.Columns.Add("ServerName", typeof(String));
dtHardware.Columns.Add("Environment", typeof(String));
}
DataRow drNewRow = dtHardware.NewRow();
drNewRow["ServerName"] = "SomeName";
drNewRow["Environment"] = "SomeEnvironment";
dtHardware.Rows.Add(drNewRow);
drNewRow = dtHardware.NewRow();
drNewRow["ServerName"] = "SomeName2";
drNewRow["Environment"] = "SomeEnvironment2";
dtHardware.Rows.Add(drNewRow);
bInitialLoad = false;
}
private void button2_Click(object sender, EventArgs e)
{
OpenMultiServerView();
}
private void OpenMultiServerView()
{
multiServerView = new Form2(dtHardware);
this.AddOwnedForm(multiServerView);
multiServerView.Show();
}
}
Form1设计器
namespace WindowsFormsApp4
{
partial class Form1
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.button2 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(308, 390);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(107, 34);
this.button1.TabIndex = 0;
this.button1.Text = "button1";
this.button1.UseVisualStyleBackColor = true;
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// button2
//
this.button2.Location = new System.Drawing.Point(437, 296);
this.button2.Name = "button2";
this.button2.Size = new System.Drawing.Size(102, 33);
this.button2.TabIndex = 1;
this.button2.Text = "button2";
this.button2.UseVisualStyleBackColor = true;
this.button2.Click += new System.EventHandler(this.button2_Click);
//
// Form1
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(679, 482);
this.Controls.Add(this.button2);
this.Controls.Add(this.button1);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);
}
#endregion
private System.Windows.Forms.Button button1;
private System.Windows.Forms.Button button2;
}
}
Form2代码
public partial class Form2 : Form
{
DataView dvServers = null;
public Form2()
{
InitializeComponent();
}
public Form2(DataTable dt1)
{
InitializeComponent();
dvServers = new DataView(dt1);
}
private void Form2_Load(object sender, EventArgs e)
{
listBox1.DisplayMember = "ServerName";
listBox1.DataSource = dvServers;
}
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
System.Windows.Forms.FormCollection fc = Application.OpenForms;
foreach (System.Windows.Forms.Form frm in fc)
{
if (frm.Name == "Form2")
{
return;
}
}
MessageBox.Show("I am the listbox event from Form2");
}
private void button1_Click(object sender, EventArgs e)
{
this.Close();
}
}
Form2 Designer
namespace WindowsFormsApp4
{
partial class Form2
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.dataGridView1 = new System.Windows.Forms.DataGridView();
this.listBox1 = new System.Windows.Forms.ListBox();
this.button1 = new System.Windows.Forms.Button();
((System.ComponentModel.ISupportInitialize)(this.dataGridView1)).BeginInit();
this.SuspendLayout();
//
// dataGridView1
//
this.dataGridView1.ColumnHeadersHeightSizeMode = System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
this.dataGridView1.Location = new System.Drawing.Point(23, 113);
this.dataGridView1.Name = "dataGridView1";
this.dataGridView1.Size = new System.Drawing.Size(749, 287);
this.dataGridView1.TabIndex = 0;
//
// listBox1
//
this.listBox1.FormattingEnabled = true;
this.listBox1.Location = new System.Drawing.Point(291, 31);
this.listBox1.Name = "listBox1";
this.listBox1.Size = new System.Drawing.Size(171, 69);
this.listBox1.TabIndex = 1;
this.listBox1.SelectedIndexChanged += new System.EventHandler(this.listBox1_SelectedIndexChanged);
//
// button1
//
this.button1.Location = new System.Drawing.Point(653, 415);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(118, 25);
this.button1.TabIndex = 2;
this.button1.Text = "button1";
this.button1.UseVisualStyleBackColor = true;
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// Form2
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(800, 450);
this.Controls.Add(this.button1);
this.Controls.Add(this.listBox1);
this.Controls.Add(this.dataGridView1);
this.Name = "Form2";
this.Text = "Form2";
this.Load += new System.EventHandler(this.Form2_Load);
((System.ComponentModel.ISupportInitialize)(this.dataGridView1)).EndInit();
this.ResumeLayout(false);
}
#endregion
private System.Windows.Forms.DataGridView dataGridView1;
private System.Windows.Forms.ListBox listBox1;
private System.Windows.Forms.Button button1;
}
}
答案 0 :(得分：2)
这是因为Form2的实例实际上并未消失。自从您调用Show以来，您就假设它已被处置是正确的，但尚未被垃圾收集器收集。实际上，无法收集它，因为在提供的代码示例中，Form1对创建的Form2实例有两个引用。
第一个在Form1.OwnedForms中。第二个是字段Form1.multiServerView。
您说过，您有几种方法可以解决此问题，例如在Form2关闭时取消绑定，但是我认为我只是放弃了这一建议。如果实际上不需要每次显示时都创建一个Form2的新实例，则可以在Form1的构造函数中创建它的一个实例，处理Form2.Closing并仅当用户关闭Form2时将其隐藏。
所以，类似...
public partial class Form1 : Form
{
//Removed bInitialLoad, we'll set up the data table in the constructor.
DataTable dtHardware = new DataTable("Hardware");
Form2 multiServerView; //No longer initalizing here, we'll do that in the constructor.
public Form1()
{
InitializeComponent();
dtHardware.Columns.Add("ServerName", typeof(String));
dtHardware.Columns.Add("Environment", typeof(String));
multiServerView = new Form2(dtHardware);
AddOwnedForm(multiServerView);
}
private void button1_Click(object sender, EventArgs e)
{
dtHardware.Clear();
//Removed the check of bInitialLoad.
DataRow drNewRow = dtHardware.NewRow();
drNewRow["ServerName"] = "SomeName";
drNewRow["Environment"] = "SomeEnvironment";
dtHardware.Rows.Add(drNewRow);
drNewRow = dtHardware.NewRow();
drNewRow["ServerName"] = "SomeName2";
drNewRow["Environment"] = "SomeEnvironment2";
dtHardware.Rows.Add(drNewRow);
//Removed setting bInitialLoad.
}
private void button2_Click(object sender, EventArgs e)
{
OpenMultiServerView();
}
private void OpenMultiServerView()
{
multiServerView.Show(); //Just show it.
}
}
public partial class Form2 : Form
{
DataView dvServers = null;
//Removed the empty constructor since Form1 no longer needs it.
public Form2(DataTable dt1)
{
InitializeComponent();
dvServers = new DataView(dt1);
}
private void Form2_Load(object sender, EventArgs e)
{
listBox1.DisplayMember = "ServerName";
listBox1.DataSource = dvServers;
}
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
MessageBox.Show("I am the listbox event from Form2");
}
private void button1_Click(object sender, EventArgs e)
{
this.Close();
}
private void Form2_Closing(object sender, FormClosingEventArgs e)
{
//Don't forget to wire it up in the designer!
//If the user clicks "button1" or the "X" then just hide the form.
if (e.CloseReason == CloseReason.UserClosing)
{
e.Cancel = true;
Hide();
}
}
}
这样，Form2的{{1}}实例永远只有一个。您不必担心Form1上的某些实例更改了数据源时已处置但尚未收集的Form2实例却触发了事件。