c# - Why this winform does not show up after Hide is called on its second iteration? -

my current situation follow:

• application injects library application b
• application uses getprocessaddress , getmodule call onstart method in library

within onstart/onstop method initiate/hide winform, in context this:

private static pluginmanager _pluginmanager; public static void onstart() {     // log file code here     if (_pluginmanager == null)     {         _pluginmanager = new pluginmanager();     }     // log file code here     _pluginmanager.show();     // log file code here }  public static void onstop() {     if (_pluginmanager != null)     {         // log file code here         _pluginmanager.hide();         // log file code here     } } 

the pluginmanager winform close event override call hide() technically(i assume) winform never disposed/closed?

• once application done tasks , close, uses getprocessaddress , getmodule call onstop method of library

everything works expected far winform shows @ onstart , hides on onstop expected.

now when start application again , calls onstart method, winform never shows up, don't error messages nor simple doesn't open.

i know function called because outputs log file line before , line after calls show().

• as title says, why winform doesn't show in second iteration?
• what else can find issue?

on further tests found out if dispose of winform , reinitialize it, winform work every call:

public static void onstart() {     // log file code here     if (_pluginmanager == null)     {         _pluginmanager = new pluginmanager();     }     else     {         _pluginmanager.dispose();         _pluginmanager = new pluginmanager();     }     // log file code here     _pluginmanager.show();     // log file code here } 

however still unaware of why required given winform never disposed of initial code.

my case off-topic? can't provide reproducible code of issue , unhappily above collect, 1 able point me in right direction or at.

this threading problem. should call .show() [stathread] , should call .hide() same thread called .show(). this:

private static isynchronizeinvoke _invoker = null;  public static void onstart() {     _invoker.invoke((action)(() => {         // log file code here         if (_pluginmanager == null)         {             _pluginmanager = new pluginmanager();         }         // log file code here         _pluginmanager.show();         // log file code here     }), null); }  public static void onstop() {     if (_pluginmanager != null)     {         // log file code here         _pluginmanager.invoke((action)(() => _pluginmanager.hide()));         // log file code here     } } 

i don't know how application's main structured, can fill in _invoker open form.

[stathread] static void main() {     application.enablevisualstyles();     application.setcompatibletextrenderingdefault(false); //    application.run(new form1());  <-- usual startup      // instead, grab object invoke on     form1 form1 = new form1();     _invoker = form1;     application.run(form1); } 

you create wholly separate stathread , call application.run(_pluginmanager) instead of pluginmanager.show().