We use the ContentControl and other containers stuff in WPF. I need the notification with the new child control is added to the container. What is the best way to get the newly created control within parent?
The ContentControl only contains a single child which is attached via the ContentControl.Content property. You can hook the ContentControl.OnContentChanged to discover when the value of this property is updated.
The cleanest way is to derive from those control and override the methods that report the changes you are interested in. For example derive from ContentControl and implement OnContentChanged. This approach may not appeal to you.
If you want to detect changes in the child or children of controls without deriving from them, you can observe that such changes will affect the layout and so you can hook the LayoutUpdated event. The problem with this approach is that you need to keep track of the children that were previously added yourself by inspecting Child or Children looking for changes. You also have to be careful not to hang onto references to former children lest you create a memory leak. But it can be done.
Related
I am developing a custom control for Windows Phone 8, which is derived from ItemsControl, will have many child objects(another custom class). It needs to have an Attached Property IsMinonAxis which should be set only once by one of the child, and not more than once. So the below code will be a problem I want to avoid.
<WPGraphControl:GraphControl>
<WPGraphControl:GraphLine GraphDataPoints="{Binding SpeedPoints}" WPGraphControl:GraphControl.IsMinonAxis="True" />
<WPGraphControl:GraphLine GraphDataPoints="{Binding AltitudePoints}" WPGraphControl:GraphControl.IsMinonAxis="True" />
</WPGraphControl:GraphControl>
The problem is attached properties are attached to child controls, and not to the parent.
In the PropertyCHangedCallback (registered as part of RegisterAttached as part of PropertyMetadata) I can get the child object for which the property is being set, but I can't access the actual control instance (this) to be able to validate the whole collection of child controls as its a static method common across all instances .
One option I am thinking is to have another attached property (internal) which will be attached when the child controls are added, and then use that property to get to parent inside the callback, and fire the validation logic. It sounds like a overly complicated logic to me.
Could you please suggest what is the best way to handle situations like this?
Might be easier to have a non-attached property on GraphControl that takes a Element to be used. Its been a while since I did WinPhone XAML, but in WPF this would look something like:
<wpgc:GraphControl MinorAxis="{Binding ElementName=Foo}">
<wpgc:GraphLine x:Name="Foo" />
<wpgc:GraphLine x:Name="Bar" />
</wpgc:GraphControl>
Since you can only assign a single value to the property, then this would ensure that only one is set.
I have a Canvas with different Elements which are created and removed dynamically at runtime inside a canvas, which itself is in a custom Usercontrol.
Now I want to add a few Touchevents, like ManipulationStarted. However, if I bind it on the Canvas, I get the canvas back as sender in my event. I need, however, the specific UIElement that was touched, so I guess I need to bind the event directly to the children. How can I achieve this?
PS: I've already tried creating a custom Event inside the Usercontrol, which is added to the specific child when it's created, however the performance seems to suffer immensely from this approach.
IIRC, the Pivot control only loads a child PivotItem if it is the currently shown child. I would then guess that the previously seen child is also somehow unloaded, presumably still stored in memory, but hidden from the UI.
What I'm wondering is, how does the Pivot control dynamically load/unload a child control, and can that behavior be imitated within a custom UserControl? As for unloading, is it as simple as collapsing the previous child's visibility, or is something trickier going on?
That is to say, supposing I use my own UserControl like:
<my:CustomUserControl>
<TextBlock x:Name="_textBlock" Text="wait for it ..." />
</my:CustomUserControl>
Normally, the child TextBlock is instantiated when the surrounding PhoneApplicationPage is instantiated, via InitializeComponent and all that. Is there any way to postpone this behavior and load the child programmatically?
Easy way to achive your goal is to use ContentControl with template. It will create all controls only after setting Contenp property.
Or you can simply inherit your control from Panel and add child controls in code.
I have an mdi child form as a dockable content in my application and I want to disable/enable a listbox in it from the parent form depending on a certain event. I thought this would be simple as:
_child.listBox1.Enabled = false;
But it doesn't seem to disable it. _child is an object reference of the mdi child form btw. Why does it not work and how can I fix this?
_child probably refers to a different instance of the child form.
Make sure that _child refers to the same instance that you called Show() on.
Can't you create a function on your MDI child which would disable the listbox, you could call from the MDI parent?
I guess that here listBox1 is private (which is the default if you have constructed your form using VS designer)
Although it works, exposing the control of a form as a public property is considered a bad design practice.
Suppose that at some point in the future, you will have to change the internal ListBox into some other type, such as ListView, in order to add some functionality.
In this scenario, if you create a method called DisableList on the form, you will only have to change one place in code, to update the way the list should be disabled.
But if you choose the method of writing code such as _client.listbox1.Enabled = false;, you will have to go through all the pieces of code that touch the ListBox, and update them.
A very important principal in design is to avoid exposing the internal implementation details of class to those that have to use it. In this case, you will benefit if the parent form won't have to know that the list is implemented as a ListBox.
I have written a custom Silverlight control based on Control. I have two DependencyProperties called Top and Bottom which both hold child controls for a specific layout display. I then use a ControlTemplate to arrange these two controls into a grid, placing one on the 0 row and the other on the 1 row. The problem I have is that I cannot seem to figure out how to get each child control's Parent property to point to my custom control. When I inspect each control at run-time, the Parent property of each is null.
This is a simple example, but I think you can see the general problem. I have a number of more complex controls that all share this problem. I know there is some magic I am missing. If a ContentControl's Content property is set to some child it is somehow setting that child's parent to itself.
Edit: A little more info
In WPF, one might use functions like AddVisualChild(), RemoveVisualChild(), AddLogicalChild(), RemoveLogicChild() to manage parent/child relationships, but these functions are not available in Silverlight.
After quite a bit of research I believe that this is not possible. I was able to recurse through the Visual Tree instead of the Logic Tree using the VisualTreeHelper to accomplish my ultimate goal.
The Parent property cannot be arbitrary, it reflects the real parent of the control for use when rendering.
From MSDN:
Parent may be a null reference (Nothing in Visual Basic) in cases where an element was instantiated, but is not attached to any logical tree that eventually connects to the page level root element, or the application object.
...
Changing an element's parent is typically only done through manipulation of collections, by using dedicated add or remove methods, or through setting content properties of elements.