I am a noob to Windows Forms so this is likely a remedial question. I have a child component with a button and a text field. I want to use multiple instances of these in a parent component or form. At runtime, when the user clicks one of the buttons, I want the parent to get the event to decide what to do with the associated text.
Coming from the long lost world of Borland C++ Builder, during design time, I would simply double-click on the buttons and handlers in the parent would be created which I could just elaborate the code. With Windows Forms, the component controls are not clickable (at design time) from the parent and are "frozen". It is not obvious to me how to pass any child button clicks to a parent. I've tried things like changing the button modifier from private to public but that doesn't help. How is this best accomplished.
Note I am using C++ as I am sharing header file definitions with an associated C++ embedded app.
-Bob
UPDATE:
My apologies, I thought I was still in my C# search :(
This is slightly complicated if you actually want to bubble up an event, or very easy if you use methods.
Methods:
In your child container, add a constructor or property that takes in and stores the parent. Then in the button handler, call this.Parent.ButtonClicked(this); and of course in the parent, add a ButtonClicked(ChildType child) method. That should get you there that way.
Custom Event:
To use events, you need to add a few things. Firstly, add a custom EventArgs class as such:
class ChildClickedEventArgs : EventArgs
{
// include a ctor and property to store and retrieve the child instance.
}
Then add a public delegate for it:
public delegate void ChildClickedEventHandler(object sender, ChildClickedEventArgs e);
Then to your child class, add a ButtonClicked event:
public event ChildClickedEventHandler ChildClicked;
And finally, a helper method to raise it:
private OnButtonClicked()
{
if (this.ChildClicked != null)
{
this.ChildClicked(this, new ChildClickedEventArgs(this));
}
}
Then when you add the child class to the parent, add an event handler for each, and you can handle your custom event for your custom control.
Alternatively:
If you can expose the Button in your child class, simply do the above but register it to this.child.Button.Clicked, saving adding the event handler yourself.
Related
<Page x:Class="ParentView">
<view:ChildView/>
<view:ChildView/>
...
</Page>
Prism attaching the child View-Models as AutowireViewModel=True. How can I gain access from ParentViewModel to the child View-Models ? (They are actually fabricated in one factory delegate that configured in the IoC container.)
protected override void OnVisualChildrenChanged(DependencyObject visualAdded, DependencyObject visualRemoved);
method isn't available in Page control, which could have been invoked upon a UIElement is added ?
How can I gain access from ParentViewModel to the child View-Models ?
The easiest way is to go the other way round: make the parent view model create the child view models, expose them as a collection-valued property, bind that to an items control and map the items to views through data templates. Everything else is unnecessarily complex and more or less hacky.
Use AutowireViewModel=true where it makes sense (i.e. if you want to use Prism's navigation), not everywhere just because you can.
I have upgraded to the latest version of MvvmCross (6.4.1) from 4.2.3. I and using Xamarin Android not Xamarin forms
In the view which initiates the dialog I do the following
Create dialog fragment derived from MvxDialogFragment
Assign a view model to it
Then call ShowView on the fragment
However when I rotate the device it fails in OnCreate with the message
Your fragment is not generic and it does not have MvxFragmentPresentationAttribute attribute set!
This did not happen in 4.2.3. The reason I create dialog this way is that I want it to use different view models depending on where I need this dialog. For example I want to show a different list of data, but in the same format in the dialog.
It seems this will only work if we apply the MvxFragmentPresentationAttribute which needs the type of view model to be defined at design time rather than run time.
Is there anything I can do to achieve this
Any help will be appreciated
If you somehow need to specify the ViewModel type at runtime, you can instead of decorating the class with the MvxFragmentPresentationAttribute let it implement, IMvxOverridePresentationAttribute and return it there with the appropriate ViewModel to be presented in.
Something like:
public class MyDialog : MvxDialogFragment, IMvxOverridePresentationAttribute
{
public MvxBasePresentationAttribute PresentationAttribute(MvxViewModelRequest request)
{
return new MvxFragmentPresentationAttribute
{
ActivityHostViewModelType = myDynamicType
};
}
}
Where you implement some kind of logic to get the myDynamicType somewhere.
However, you should be able to use MvxDialogFragmentPresentationAttribute instead though and the presenter will attempt to use the topmost Android Activity to present it in if you provide a null ref as the ActivityHostViewModelType.
I have a Content View in Xamarin forms with 2 StackLayout horizontally aligned in it. I want to change the Content of the 2nd Stacklayout dynamically, but I don't want to use Master details page in that case. Please find an attachment to see what my UI looks like. I want to load different pages in StackLayout 2 on button clicks in StackLayout 1.
Update: I want to achieve above using MVVM.
You specifically said you want to load different pages inside Stacklayout2.
Out of the box, this is not possible. A Page can not be nested inside another view in Xamarin.Forms*
However, you most likely don't need to nest a whole page either, which is good news.
You can create custom xaml views as separate xaml files, and then reference them like regular controls. For example you would create a xaml file MyDataView, inside you could use a and fill it out with your different labels, entries and what nots, then instantiate and add that MyDataView inside your page like you would any other control.
For your host page, I would recommend you change your StackLayout2 to a ContentView, as it will only ever contain one view, which in case of something like your custom "MyDataView" from above, would actually contain the stack layout and all the details.
From the point of view of your page, it has the left layout with all the buttons, and it has the "container" on the right to host different complex views. So it does not need a stacklayout there.
There is also an important decision that you need to make on when and how you want to instantiate all the views that you will host inside the right pane.
You might choose to instantiate them all at once, when loading the page, if there aren't too many. Then switchig to each one during page use should be quite quick. Something like this:
public partial class MainPage
{
private MyDataView myDataView = new myDataView();
private OtherView otherView = new OtherView();
private ThirdView thirdView = new ThirdView();
public void OnSomeButtonClick(object sender, EventArgs e)
{
Container.View = myDataView; //Container would be the x:Name you gave to your ContentView control on the right side of the page that will host the different views
}
}
Or you might prefer to "lazy" instantiate the views, which would only instantiate the view the first time it is navigated to. This is useful if some views will never actually be accessed, and you can save some cpu cycles and ram by not loading the view until it's needed. The downside of course is when you do load it for the first time, it will load slower. Like this:
public partial class MainPage
{
private MyDataView myDataView;
private OtherView otherView;
private ThirdView thirdView;
public void OnSomeButtonClick(object sender, EventArgs e)
{
if (myDataView == null) myDataView = new MyDataView();
Container.View = myDataView; //Container would be the x:Name you gave to your ContentView control on the right side of the page that will host the different views
}
}
And finally you can instantiate the view everytime it is needed. I would not go with this route in most cases. Unless you really specifically need to recreate the entire view each time (like if you are dynamically changing it during use, and you need to reset it when it's shown again)
*I have seen a custom renderer implementation that nested a whole page inside a view on github. I did not test it as it was not completely implemented at the time.
Cant you do something like this:
button1.OnClick += (sender, args) =>{
StackLayout2.Children.Remove(currentview);
StackLayout2.Children.Add(newview);
}
Not sure if its called onclick or clicked.
I'm starting to use the MVVMLight framework and have a question about binding to properties in the ViewModel. I found that I have to call the RaisePropertyChanged method in the setter for the property in order for the View to be updated. And I have to call RaisePropertyChanged from through the dispatcher otherwise I get a thread access error.
public string Lat { get { return _lat; } set
{
_lat = value;
Deployment.Current.Dispatcher.BeginInvoke(() => RaisePropertyChanged("Lat"));
} }
This works but its a lot of code to get auto binding properties. Is there a helper to handle this more cleanly?
Raising PropertyChanged events is mandatory when you want to bind UI elements to properties on your model classes, independently of whether you're using MVVM Light or not. In fact it's easier with MVVM Light as it provides the RaisePropertyChanged method, which you would otherwise have to code yourself. :)
Using Dispatcher.BeginInvoke() is only needed if the set accessor of your property can be invoked from a thread different from the UI thread. Otherwise it's OK to call RaisePropertyChanged directly.
In my winforms app, I have a UserControl that contains a DataGridView. I instantiate and load this UserControl when needed into a panel in my Main Form (frmMain). My problem is figuring out how to resond to or listen for events raised in my UC's DataGridView. For example, I want to handle the CellDoubleClick event of the DataGridView in my Main Form rather than through the UC.
Is this possible? I had thought of updating a property when the cell in the grid is double-clicked, and then let my Main form do whatever when that property changes - therefore I thought of using INotifyPropertyChanged. Im not heavily clued up on how to use it in m scenario however, and would deeply appreciate some help in this regard, or if anyone can suggest an alternate solution.
Much thanx!
Your user control must encapsulate some logic, so if you want to handle event of the DataGridView that is in your control the way you've described, you probably missing something in idea of user controls and encapsulation. Technically here two ways to do this:
Make a public property in your user control of type DataGridView.
Make an event wrapper. You will need to create an event in your user control that is raised when DataGridView CellDoubleClick (or any) is rased and in your calling code you will handle this event wrapper.
The second approach is more logical, cos internal logic of your control is incapsulated and you can provide end-user of you component with more logical and meaningful event then CellDoubleClidk or else.
thank u 4 your reply. Sorry for not responding earlier. I did manage to sort this issue out by creating a public event in my UC:
public event DataGridViewCellEventHandler GridRowDoubleClick {
add { dgvTasks.CellDoubleClick += value; }
remove { dgvTasks.CellDoubleClick -= value; }
}
and in my main form, after I instantiate and load the UC
_ucTask.GridRowDoubleClick += new DataGridViewCellEventHandler(TasksGrid_CellDoubleClick);
with the following attached event:
private void TasksGrid_CellDoubleClick( object sender, DataGridViewCellEventArgs e ) {
// do work here!
}
This does work, although I don't know if any of u experts out there foresee a problem with this approach.