我有一个 Windows 窗体应用程序，它的运行方式我不理解。为了清晰起见，我创建了一个简单的应用程序，以最少的逻辑重现功能。它有两种形式。
表格1: 有一个按钮 1，单击该按钮可将行添加到数据表中。 有一个按钮2，用于显示表单并将数据表发送到表单。
表格2: Form2 从数据表创建数据 View 并将数据 View 绑定(bind)到列表框。 Form2 还有一个在表单上执行 this.Close() 的button1。我读到用 formName.Show() 打开的任何内容都将在 .Close 期间被处理。
这就是事情变得奇怪的地方。每次清除数据表并再次添加行时，都可以反复单击 Form1 按钮 1。一旦单击 from1 按钮 2，显示表单 2，然后关闭，返回到表单 1 并单击按钮 1 会引发错误。该错误来自 form2(已关闭)listBox1_SelectedIndexChanged 事件。
问题是，为什么在消失的窗体上消失的控件会触发事件？ 我找到了几种方法来避免这种情况，但我想了解为什么会发生这种情况，例如设置列表框数据源= null，但想知道发生了什么......花了半天时间试图弄清楚这一点。 SO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 设计器
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;
}
}
最佳答案
这是因为 Form2 的实例实际上并没有消失。您正确地假设它已被处置，因为您调用了 Show，但它尚未被垃圾收集器收集。事实上，它无法被收集，因为在提供的代码示例中 Form1 有两个对其创建的 Form2 实例的引用。
第一个位于 Form1.OwnedForms 中。第二个是字段 Form1.multiServerView。
您说过您有几种方法可以修复它，例如在 Form2 关闭时打破绑定(bind)，但我想我应该放弃这个建议。如果您实际上不需要每次显示时都创建 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 并在用户关闭时隐藏 Form2。
所以，就像......
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，Form1 就只有一个 Form2 实例。您不必担心 Form2 的实例已被释放但尚未收集，但当 Form1 上的某些内容更改数据源时会触发事件。
关于c# - 代码在其所在表单被关闭并处理后执行，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/56563594/