Creating Event Handlers in Windows Forms

An event handler is a procedure in your code that determines what actions are performed when an event occurs, such as when the user clicks a button or a message queue receives a message. When an event is raised, the event handler or handlers that receive the event are executed. Events can be assigned to multiple handlers, and the methods that handle particular events can be changed dynamically. You can also use the Windows Forms Designer in Visual Studio to create event handlers.

In This Section

Events Overview
Explains the event model and the role of delegates.

Event Handlers Overview
Describes how to handle events.

How to: Create Event Handlers at Run Time for Windows Forms
Gives directions for responding to system or user events dynamically.

How to: Connect Multiple Events to a Single Event Handler in Windows Forms
Gives directions for assigning the same functionality to multiple controls through events.

Order of Events in Windows Forms
Describes the order in which events are raised in Windows Forms controls.

How to: Create Event Handlers Using the Designer Describes how to use the Windows Forms Designer to create event handlers.

Related Sections

Events
Provides links to topics on handling and raising events using the .NET Framework.

Troubleshooting Inherited Event Handlers in Visual Basic
Lists common issues that occur with event handlers in inherited components.

Получить handle главной формы

Одна надежда на вас, я запутался окончательно. Как не пытаюсь передать handle родительского окна на дочернее — тщетно. Хоть txt в TEMP создавай, лишь бы не видеть эти ошибки доступа и просьбы указать ссылку на объект.

В общем нужно получить handle родительского (оно же и главное) окна с дочернего окна.

Добавлено через 14 минут
/close

Начал паниковать раньше времени, вот решение:
IntPtr MainHandle = Process.GetCurrentProcess().MainWindowHandle;

Добавлено через 27 минут
И да, переменную надо задавать в FormLoad, иначе будет 0, тк может выполнится до полной загрузки главной формы

Получить количество элементов ListView главной формы
меня такой вопрос, почему с дочерней формы в ListView данные выгружаютса без проблем а вот.

Взаимодействие между формами. Получить массив и переменную с главной формы
Здравствуйте, возникла задача получить массив и переменную с главной формы. Код главной формы.

Как из класса получить доступ к элементу дочернего окна главной формы?
Есть структура MDI — Главная форма-дочерняя. И есть класс. Из класса мне нужно получить данные о.

System.StackOverflowException при обращении к элементу главной формы из дочерней формы
При закрытии дочерней формы (client) необходимо обратиться к элементу listView1 главной формы.

Заказываю контрольные, курсовые, дипломные и любые другие студенческие работы здесь или здесь.

Передать фильтр изображения из combobox формы на pictureBox главной формы
Приветствую, форумчане. Возникла проблема. Есть форма, в которой хранятся фильтры для.

Из дочерней формы убрать событие из объекта главной формы (а потом обратно добавить)
Есть основная форма, которое я называю главной формой. Создаю дочернюю форму — «Настройки», на.

Передача параметров из дочерней формы в класс, унасле́дованный от главной формы
Добрый день, форумчане. Сильно не пинайте. Ситуация такая: из главной формы вызываю дочернюю.

Чтоб Дочерние формы открывались по иерархии от главной формы
Есть главная форма Form1, Form1 — topmost=true, т.е Form 1 отображается поверх всех окон. Нужно.

WinForms main window handle

In my winforms application I am trying to get a main window handle, so I can set it as parent to my wpf modal window. I am not too experienced with winforms, so after a bit of googling I found two ways to get it.

(1) seems to always return the same value which appears to be correct (at least my modal window behaves as expected), while (2) sometimes returns the same value as (1), but sometimes — an entirely different pointer, which does not seem to work (my modal window appears on top of every other window, not just the parent window).

Can someone explain the difference between the two methods? Is it normal that sometimes they return different results?

Edit:

In case anyone else is wondering: once you get the handle, you can use it by creating WindowInteropHelper class:

1 Answer 1

It is certainly not unusual for Process.MainWindowHandle to return the wrong handle. The Process class has to make a guess at which window is the «main» one. There is no mechanism in the native winapi to designate a window as such. So Process makes a guess that the first window is the main one. This has a knack for going wrong in apps that use a splash screen or a login dialog, etc, or create a window on another thread.

Application.OpenForms doesn’t have this problem, but has a failure mode, it will lose track of a window when it is recreated. Which happens when the program changes certain properties of the Form that can only be specified when the window is created. The ShowInTaskbar, TransparencyKey and Opacity properties are the most common troublemakers.

The most reliable way is to override the OnHandleCreated() method of the form you want to be the parent. Which is called whenever the Handle property changes. Do note that you want to make sure that this doesn’t happen while your WPF window is active, that will kill the WPF window as well. Otherwise easy to observe of course 🙂

Winforms issue — Error creating window handle [duplicate]

We are seeing this error in a Winform application. Can anyone help on why you would see this error, and more importantly how to fix it or avoid it from happening.

10 Answers 10

Have you run Process Explorer or the Windows Task Manager to look at the GDI Objects, Handles, Threads and USER objects? If not, select those columns to be viewed (Task Manager choose View->Select Columns. Then run your app and take a look at those columns for that app and see if one of those is growing really large.

It might be that you’ve got UI components that you think are cleaned up but haven’t been Disposed.

Here’s a link about this that might be helpful.

The windows handle limit for your application is 10,000 handles. You’re getting the error because your program is creating too many handles. You’ll need to find the memory leak. As other users have suggested, use a Memory Profiler. I use the .Net Memory Profiler as well. Also, make sure you’re calling the dispose method on controls if you’re removing them from a form before the form closes (otherwise the controls won’t dispose). You’ll also have to make sure that there are no events registered with the control. I myself have the same issue, and despite what I already know, I still have some memory leaks that continue to elude me..

See this post of mine about «Error creating window handle» and how it relates to USER Objects and the Desktop Heap. I provide some solutions.

This problem is almost always related to the GDI Object count, User Object count or Handle count and usually not because of an out-of-memory condition on your machine.

When I am tracking one of these bugs, I open ProcessExplorer and watch these columns: Handles, Threads, GDI Objects, USER Objects, Private Bytes, Virtual Size and Working Set.

(In my experience, the problem is usually an object leak due to an event handler holding the object and preventing it from being disposed.)

Well, in my case it was definitely the USER Objects that were out of control. I looked in the Windows Task Manager and sure enough, the USER Objects count was at 10’000 exactly.

I am dynamically embedding property and list sheets in Tab Pages by setting the Parent property of the property or list sheet’s container panel to that of the Tab Page. I am conditionally recycling or re-creating the property and list sheet forms depending on the type of collection being listed or class type of the object being inspected.

NB: In Delphi, all controls had an Owner and a Parent property. Even if one changed the Parent property of a control, it would still be disposed by its owner when the owning control got destroyed.

Native Window. On Handle Change Метод

Определение

Задает метод уведомления, вызываемый при изменении дескриптора окна. Specifies a notification method that is called when the handle for a window is changed.

Примеры

В следующем примере кода показано создание окна с заданным именем класса окна операционной системы. The following code example demonstrates creating a window with a specific operating system window class name. В примере создается класс, наследующий от, NativeWindow для выполнения этого. The example creates a class that inherits from NativeWindow to accomplish this. В примере также демонстрируется переопределение OnHandleChange метода для получения уведомлений об Handle изменениях. The example also demonstrates overriding the OnHandleChange method to be notified when the Handle changes.

MyNativeWindow Класс создает новое окно с параметром, имеющим ClassName значение BUTTON . The MyNativeWindow class creates a new window with the ClassName set to BUTTON . При этом создается окно кнопки Win32. This creates a Win32 button window. Задается расположение и размер кнопки, а также задаются дополнительные стили окна. The location and size of the button is set, along with specifying additional window styles. Класс демонстрирует использование CreateHandle метода и переопределение WndProc метода для перехвата полученных сообщений окна. The class demonstrates how to use the CreateHandle method and override the WndProc method to intercept window messages that are received. Хотя в примере выполняется поиск WM_ACTIVATEAPP сообщения, это можно заменить в реальной программе с помощью оконных сообщений, относящихся к созданному типу. Although the example looks for the WM_ACTIVATEAPP message, this can be replaced in a real program with window messages specific to the type created.

Этот код является выдержкой из примера, показанного в NativeWindow обзоре класса. This code is an excerpt from the example shown in the NativeWindow class overview. Для краткости не указан некоторый код. Some code is not shown for the purpose of brevity. NativeWindowПолный листинг кода см. в разделе. See NativeWindow for the whole code listing.

Некоторые типы элементов управления отправляют сообщения окна в родительском окне, а не в окне. Some control types send their window messages to the window parent instead of the window. Дополнительные сведения см. в разделе Windows Platform SDK. See the Windows Platform SDK for more information.

Комментарии

Этот метод вызывается при Handle изменении значения свойства. This method is invoked when the value of the Handle property has changed.

Примечания для тех, кто наследует этот метод

Переопределите этот метод, чтобы отслеживание изменений, внесенных в обработчик окна. Override this method to track changes that are made to the window handle.