Readonly Reference To Parent/collection?
Feb 22, 2011
When it comes to creating trees or collections, sometimes I want child elements to have a reference to the parent. Obviously it is important that the parent and child references to each other remain in sync. It seems natural to have code in the parent "addchild" and "removechild" methods that updates the child's parent reference.t also, the reference to the parent should probably be readonly, so it can only be changed at the appropriate time.Two examples in .Net that I've seen are the TreeNode and datagridview controls
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Jul 28, 2010
Is there a efficient way to provide an Enumarable<SomeType> or a collection that implements INotifyCollectionChanged but that can only be changed from the inside of the providing class.
The following example shows what I mean, but has the disadvantage that the caller can cast the IEnumerable<SomeType> back and then manipulate my internal collection, what I really would dislike:
[Code]...
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Feb 19, 2010
I have a custom collection, lets says COL, that derives from ObjectModel.Collection. I have my own collection editor that works fine when a property, of type COL, is Read and Write enabled. However, if I change the property to ReadOnly, the open editor button stops showing in the property grid. As a test, I override my custom editor with the CollectionEditor, and that worked fine. So, my question is, what check is the property grid making, that CollectionEditor passes but my collection editor fails?
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Mar 3, 2010
I have a class that has a readonly collection property - Its a list of extender providers that have been applied to the control.I've implemented a simple property descriptor for the collection so that the property can be expanded in the property grid to examine each entry.
When I select an extender provider and set it to false, I remove it from the collection. The GetProperties method of the type converter is requeried and the property grid refreshes.However, when I set an extender provider to true, and thus add it to the collection, GetProperties is not requeried.
Somehow, the property grid is making a distinction between adding to and removing from the collection. Or alternativly, its refreshing when an extender provider is added, but not when one is removed.
[Code]...
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Oct 7, 2008
Using MDI in .net, how do you reference a control on a parent form from a child? Like, if on the parent I have a textbox called txtBox1, what could I do from the child form to read the contents? I've been googling unsuccessfully all day. The closest I've found is
Parent!ControlName.Property
I don't know what the ! is supposed to mean, but I get an error here: Class 'System.Windows.Forms.Control' cannot be indexed because it has no default property.
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Mar 27, 2009
i have a user define object which i'm initializing with data from external datafiles.... the purpose of this object is to reduce the amount of disk/data access and processing required every time i need to add an instance of this object to a collection.so, whenever i add a copy of this object to a collection, i would simply reference the "base" object, and avoid having to process all the data and perform the conversion and so on...the issue is when i add the object
Collection.add(Base_Object, Key)
the collection ITEM is a Reference to the base object and not a copy.
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Apr 18, 2011
I often have a class defined and I also define another class that is simply a collection of the other class. To do this I found it easiest just to define the other class as Inherits List(Of Type). The reason I define a collection class is to add extra functionality to the collection. Take the following code for example.
Class Car
Property Name As String
Property Year As Short
[Code]....
how can I define my own collection so that I can reference it by index or name like that. Right now I can only reference it by index.
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Mar 2, 2010
I've tried this example directly from MSDN:
Dim Screens() As System.Windows.Forms.Screens
and I can't find a way to get a reference to the Screen. I've checked my references and they seem fine but I may have missed something. Anyone experience this or know of a bug?
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Jan 6, 2010
I am writing a simple control translation function that reads an XML file containing control names and their localized text. Within the application, each time a form is loaded, it iterates through every control and tests to see if that control is defined in the XML file. If it is, it then sets the control text to whatever localized text is defined in the XML file.
There are some tests and additional requirements (i.e. nested loops) for TabControl and MenuStrip etc., but the control that is giving me the most trouble is the ContextMenuStrip.[code]...
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Mar 30, 2010
I have a datagridview control on a form that I want to make readonly, before showing the form. I can disable it before showing the form with the [code]...
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Feb 27, 2012
VB Reference parent member of a class through a child when using List Of(T)?
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Jun 12, 2012
I am using a PropertyGrid control to edit my class properties and I am trying to set certain properties read-only depending on other property settings.This is the code of my class:
Imports System.ComponentModel
Imports System.Reflection
Public Class PropertyClass[code].....
This is the code I am using to edit the values:
Dim c As New PropertyClass
PropertyGrid1.SelectedObject = c
The problem is that when I set SomeProperty to True, nothing happens and when I then set it to False again it sets all properties Read-Only.
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Nov 11, 2011
I have an error while using a collection that has been stumping me for years.I wrote a class to allow users to write equations in a txt file using RPN (stack based notation).The class runs through a select statement while reading the equation and then ends up with a final number as the answer. I have a collection to place these objects in for easy reference. For whatever reason I get random object reference not set to an instance of an object errors when there is nothing in the program that would remove objects from the collection, kill objects, or change the collection in any way. It is possible for one thread to call the calculate function while another thread calls the CurrentValue property. I'm not sure if this could be causing the error, but once it happens I get an error every time the program enters that code until I run out of memory.
[Code]...
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Jun 30, 2010
Okay I've been wondering about this for a while now, but whenever you assign variable values to objects they tend to just become references to the original object
For example:
Dim copiedCollection As ListBox.ObjectCollection = ListBox1.Items
For Each L As String In copiedCollection
If L = "Goodbye" Then ListBox1.Items.Remove(L)
Next
As soon as it encounters the string "Goodbye" and removes the item from the listbox, the program will throw an error saying the the collection (copiedCollection) has been modified. How can I make copiedCollection a true copy (not a reference) to the Listbox1.Items collection?
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Dec 1, 2011
I am working on a application that has quite a few functions involved and have been thinking of the following: If I have a function that has a few paramaters, is it more efficient to pass the objects to the function(Example 1) or reference the objects in the parent(Example 2)? Does it matter if the objects are large or not?
Example:
Class mainform
Public myGenericList As New List(Of String)
Public myDatarowArray() As DataRow
[Code].....
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Apr 11, 2009
I have a 'property management class' that contains several functions and properties. I have several other classes that use the 'management class' as a property to derive the value of several of its other properties.Is there a way for me to reference the outer class from the 'management class' functions without having to pass it as a parameter? I ask because several different classes can have this 'management class' as a property and am having a hard time typing the parameter.
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Jan 2, 2010
I have a Parent Class Called Fuselage that containsfour child classes called Forebody, CenterBody, AftBody, and CrossSection. CrossSection classcontains objects common to Forebody, CenterBody, and Aftbody (example: width). How do I access thewidth property in CrossSection from within the classForebody?
Public Class Fuselage
Dim Forebody As ClsSection
Dim Centerbody As ClsSection
[code].....
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Jul 28, 2009
I'm not sure exactly if the folder icon is in shell32.dll, but nonetheless if it is.Basically, whenever I come across a folder in a FileSystem list, I want to add the icon for a folder to the image list that I am using for the ListView. The problem is that I'm not sure how to reference a specific icon location in a icon collection in a dll.Is this possible with Icon.ExtractAssociatedIcon and shell32.dll?
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Apr 20, 2012
I have a UserControl named DataGridViewFilterAndSorter that I built using a SplitContainer. In each Panel of the SplitContainer contains a FlowLayoutPanel and in each FlowLayoutPanel contains a LinkLabel.
I have a procedure that accepts a reference to one of the FlowLayoutPanels in the UserControl. I want to get a reference to the UserControl (DataGridViewFilterAndSorter) using the FlowLayoutPanel reference. Currently, I have to use this[code]...
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Aug 3, 2011
This is a challenging one that got me stumped while I was coding today. Suppose I am running the Sub Test1() and Test2() and would like to print out the value of the Shadows method of the instance of the object I am passing in to TestCall() (see below - it is clearer) using the following restrictions:
Can't change the contents of Class A, B, and C
Can't change Sub Test1() and Sub Test2()
TestCall() can't have an if, select case etc. statement that tries to figure out the type
[code].....
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Jun 24, 2009
I have a main form, and some sub forms, and each sub form can have some sub forms. When I have multiple sub forms open, and I try to get data from the parent form, it returns the data from the wrong parent form.For example I have two instances of Mainform.subform running. If I do something like this in a child form of one instance of the subform. It returns data from the other subform.
dim l = Mainform.subform.listofdata
Edit:I am using visual Studio 2008. Winforms, form designed using designer. In my mainform I am doing this
Protected Friend frmMain as Mainform
frmmain = new mainform
In frmMain I am doing this
Protected Friend frmsub as new Subform'
frmsub = new subform
[code]....
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Apr 10, 2010
I would like to know if there is some simple code to release a child control from it's parent control, without having to name the parent control. In pseudocode, I'm looking for something like this:
[Code]...
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Jan 15, 2010
Is it good practice to store sub-collections of item X inside a parent collection of item X for caching 'filter-queries' which are performed on the parent collection? (They won't be used together (as in color AND type).) Or is it also ok to just Loop over the collection and return the correct entities in a temporary collection?
[Code]...
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Sep 7, 2011
I have the following classes:
Product, Service and OrderItem
Product and Service must inherit OrderItem. So basically I want to store OrderItem object in my shopping cart and these object are store in a list.
Public MustInherit Class OrderItem
Private m_enuItemType As TypeOfItem = TypeOfItem.None
Private m_strUserID As Integer[code].....
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Feb 8, 2010
I have been researching for a couple of days now and to no avail. Does Anyone know how to make a custom collection that take advantage of the collection editor? I would like to be able to have 3 Color Values, 1 Boolean and 1 String.
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Jul 25, 2011
I'm trying to support Basic.NET on my framework so I'm trying to convert C# 4 code to Basic.NET 10. Microsoft is committed to "co-evolve" these two but I'm having a problem with collection initialization... I found that I can initialize a collection much like in C#:
[Code]...
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Apr 15, 2009
I've got the following ADO.NET Entity Framework Entity Data Model:I want to find all the Policyholders with both a Service of a given Id and also a Keyword of a given Status.
This LINQ Does Not Work:
Dim ServicesId As Integer = ...
Dim KeywordStatus As Integer = ...
Dim FoundPolicyholders = From p As Policyholder In db.PolicyholderSet.Include("Keywords").Include("Services") _
Where p.Services.Id = ServicesId _
And p.Keywords.Status = KeywordStatus _
Select p
The Where clause cannot search the p.Services and p.Keywords EntityCollections in that way.
[Code]...
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Apr 6, 2012
currently in my application I have a Global Collection that is a Collection of Collections.Currently I am trying to add items/ elements to one of the child collections of the Global Collection but I am unable to use the collections methods of the child.When I assign a variable to the child collection and return the collection it is just an object with the collection inside.
Ex:
Dim GlobalCollection as New Collection
Dim ChildCollection1 as New Collection
Dim tempCurrentCollection[code]......
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Dec 17, 2009
I've been working with a CMS called InsiteCreations 2008. I'm running into an error I just can't wrap my head around. I would even be willing to compensate anyone a small amount over paypal, for a solution. The error is rare in occurance, and appears when clicking about 3-4% of links to other pages within our CMS.The full code page is quite large, but there seems to be only one function associated with the error. The error also only appears when not logged into the CMS. If logged into the CMS, clicking the link simply displays the page as normal. I have already checked permissions on the page from the CMS admin console, and it is public.
The error message is as follows:
Server Error in '/' Application.Collection index must be in the range 1 to the size of the collection.
Description:
An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
[code]....
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Apr 15, 2011
search the collection of a collection in my LINQ Where clause?
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