我们在Winform开发的时候，使用From.Show来显示窗口，使用Form.Close来关闭窗口。熟悉Winform开发的想必对这些非常熟悉。但是Form类型实现了IDisposable接口，那我们是否需要每次关闭窗口后都去调用Dispose呢？对于这个问题我们可以查看一下Form的源码。
Form.Close
代码语言：javascript复制 public void Close()
{
if (this.GetState(262144))
throw new InvalidOperationException(SR.GetString("ClosingWhileCreatingHandle", new object[1]
{
(object) "Close"
}));
else if (this.IsHandleCreated)
{
this.closeReason = CloseReason.UserClosing;
this.SendMessage(16, 0, 0);
}
else
base.Dispose();
}很明显这个方法有3个分支。第一个分支是关闭出现异常的情况，第二个分支是句柄已经创建的时候执行，很明显第三个分支的时候直接调用了基类的Dispose方法。大部分时候窗口调用Close时句柄肯定是被创建了，那就会进入第二个分支。很明显第二个分支没有调用Dispose，那是不是真的呢？继续跟进去。SendMessage internal IntPtr SendMessage(int msg, int wparam, int lparam)
{
return UnsafeNativeMethods.SendMessage(new HandleRef((object) this, this.Handle), msg, wparam, lparam);
}调了一个静态方法继续进去 [DllImport("user32.dll", CharSet = CharSet.Auto)]
public static IntPtr SendMessage(HandleRef hWnd, int msg, int wParam, int lParam);明白了吧。SendMessage其实是调用了user32.dll的API，向指定的窗口发送消息。这里就是向自己发送一个消息，注意msg=16哦。既然有发送消息的，那肯定得有拦截消息的方法啊。（这里多扯一句，.NET Winform使用了事件驱动机制，事件机制其实也是封装了消息机制。）
WndProc
代码语言：javascript复制 protected override void WndProc(ref Message m)
{
switch (m.Msg)
{
case 529:
this.WmEnterMenuLoop(ref m);
break;
case 530:
this.WmExitMenuLoop(ref m);
break;
case 533:
base.WndProc(ref m);
if (!this.CaptureInternal || Control.MouseButtons != MouseButtons.None)
break;
this.CaptureInternal = false;
break;
case 546:
this.WmMdiActivate(ref m);
break;
case 561:
this.WmEnterSizeMove(ref m);
this.DefWndProc(ref m);
break;
case 562:
this.WmExitSizeMove(ref m);
this.DefWndProc(ref m);
break;
case 288:
this.WmMenuChar(ref m);
break;
case 293:
this.WmUnInitMenuPopup(ref m);
break;
case 274:
this.WmSysCommand(ref m);
break;
case 279:
this.WmInitMenuPopup(ref m);
break;
case 167:
case 171:
case 161:
case 164:
this.WmNcButtonDown(ref m);
break;
case 71:
this.WmWindowPosChanged(ref m);
break;
case 130:
this.WmNCDestroy(ref m);
break;
case 132:
this.WmNCHitTest(ref m);
break;
case 134:
if (this.IsRestrictedWindow)
this.BeginInvoke((Delegate) new MethodInvoker(this.RestrictedProcessNcActivate));
base.WndProc(ref m);
break;
case 16:
if (this.CloseReason == CloseReason.None)
this.CloseReason = CloseReason.TaskManagerClosing;
this.WmClose(ref m);
break;
case 17:
case 22:
this.CloseReason = CloseReason.WindowsShutDown;
this.WmClose(ref m);
break;
case 20:
this.WmEraseBkgnd(ref m);
break;
case 24:
this.WmShowWindow(ref m);
break;
case 36:
this.WmGetMinMaxInfo(ref m);
break;
case 1:
this.WmCreate(ref m);
break;
case 5:
this.WmSize(ref m);
break;
case 6:
this.WmActivate(ref m);
break;
default:
base.WndProc(ref m);
break;
}
}WndProc就是用来拦截窗口消息的。看一下代码，Form重写了这个方法，一个很简单的switch。Case 16调用了 WmClose方法，继续跟进去。
WmClose
代码语言：javascript复制private void WmClose(ref Message m)
{
FormClosingEventArgs e1 = new FormClosingEventArgs(this.CloseReason, false);
if (m.Msg != 22)
{
if (this.Modal)
{
if (this.dialogResult == DialogResult.None)
this.dialogResult = DialogResult.Cancel;
this.CalledClosing = false;
e1.Cancel = !this.CheckCloseDialog(true);
}
else
{
e1.Cancel = !this.Validate(true);
if (this.IsMdiContainer)
{
FormClosingEventArgs e2 = new FormClosingEventArgs(CloseReason.MdiFormClosing, e1.Cancel);
foreach (Form form in this.MdiChildren)
{
if (form.IsHandleCreated)
{
form.OnClosing((CancelEventArgs) e2);
form.OnFormClosing(e2);
if (e2.Cancel)
{
e1.Cancel = true;
break;
}
}
}
}
Form[] ownedForms = this.OwnedForms;
for (int index = this.Properties.GetInteger(Form.PropOwnedFormsCount) - 1; index >= 0; --index)
{
FormClosingEventArgs e2 = new FormClosingEventArgs(CloseReason.FormOwnerClosing, e1.Cancel);
if (ownedForms[index] != null)
{
ownedForms[index].OnFormClosing(e2);
if (e2.Cancel)
{
e1.Cancel = true;
break;
}
}
}
this.OnClosing((CancelEventArgs) e1);
this.OnFormClosing(e1);
}
if (m.Msg == 17)
m.Result = (IntPtr) (e1.Cancel ? 0 : 1);
if (this.Modal)
return;
}
else
e1.Cancel = m.WParam == IntPtr.Zero;
if (m.Msg == 17 || e1.Cancel)
return;
this.IsClosing = true;
if (this.IsMdiContainer)
{
FormClosedEventArgs e2 = new FormClosedEventArgs(CloseReason.MdiFormClosing);
foreach (Form form in this.MdiChildren)
{
if (form.IsHandleCreated)
{
form.OnClosed((EventArgs) e2);
form.OnFormClosed(e2);
}
}
}
Form[] ownedForms1 = this.OwnedForms;
for (int index = this.Properties.GetInteger(Form.PropOwnedFormsCount) - 1; index >= 0; --index)
{
FormClosedEventArgs e2 = new FormClosedEventArgs(CloseReason.FormOwnerClosing);
if (ownedForms1[index] != null)
{
ownedForms1[index].OnClosed((EventArgs) e2);
ownedForms1[index].OnFormClosed(e2);
}
}
FormClosedEventArgs e3 = new FormClosedEventArgs(this.CloseReason);
this.OnClosed((EventArgs) e3);
this.OnFormClosed(e3);
base.Dispose();
}WmClose这个方法略有点复杂，主要是用来出发OnCloseing,OnClosed等事件。看看最后，它终于调用了base.Dispose()。看来Close方法确实会自动调用Dispose。是吗，不要高兴的太早。仔细看看前面的代码，if (this.Modal) return; 看到没，当窗口是模态的时候，方法直接return了。
总结
到这里就差不多了。所以当我们使用ShowDialog来显示窗体的时候，当你关闭的时候，最好手动Dispose一下。为什么是最好呢，因为其实在GC回收垃圾的时候还是会调用窗体的Dispose的，因为在Form的基类的终结器里面有调用Dispose(false);
代码语言：javascript复制 ~Component()
{
this.Dispose(false);
}其实在MSDN上微软就对这有说明，顺便吐槽一下中文MSDN的翻译，实在是太烂了。
有2种情况下需要手工调用Dispose： 1. 窗口是MDI的一部分且是不可见的
2.模态的时候 第二种情况就是现在说的，但是第一种情况我测试了下，没有复现出来，MDI里面的子窗口调用Close的时候跟正常一样，每次都会自动Dispose。试了很久还是一样的结果，求高人指定吧。
代码语言：javascript复制.csharpcode, .csharpcode pre
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