Question:
Perhaps the challenge could be stated this way: How do I bind a single property in a content page to a globally stored variable in Xamarin Forms?
Details:
I am using the MVVM pattern. I have a navigation content page (1 of 3 such pages) with a Picker object which is populated dynamically from the collectionModel and said model is read/write. I am attempting to persist the SelectedItem (or index, whichever is most appropriate) thru all 3 content pages such that navigation from page to page shows the same item (from the user's perspective). How should I do this?
I can set the Picker.SelectedIndex manually in ContentPage_Appearing() event. I would much rather use binding.
Follow these steps:
Create a static class, like this:
public static class DataClass
{
public static int PickerSelectedIndex = 0;
}
Add the xmlns:local in ContentPage mark in each Content Page, like this:
xmlns:local="clr-namespace:DataPersist"
Binding the data for your controls in each page's Xaml, like this:
<Picker x:Name="picker" SelectedIndex="{x:Static local:DataClass.PickerSelectedIndex}">
It works like this:
Related
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.
My EmberJS app is confusing me a lot at the moment. I have a collection view, that in turn defines an itemViewClass of a custom view I have defined in my code. Something like:
App.CarouselView = Ember.CollectionView.extend({
itemViewClass: App.SlideView.extend(),
});
And this CarouselView is rendered inside a template that has a dynamic segment backing it (I hope this makes sense?) . The controller for these dynamic segment is an array controller because the model for these dynamic segments is a collection :) (more confusion, please let me know)
App.SlidesController = Ember.ArrayController.extend();
By now all of you have figured that I am basically rendering a bunch of slides inside of a carousel. And these are dynamically backed in the collectionView by setting the property
contentBinding:'controller' // property set in CarouselView, controller corresponds to SlidesController
The confusion begins now. I want to add a slide to the existing set of slides. So I provide a button with an action : 'add' target='view'
In the SlidesView,
actions:{
add: function(){
var carouselView = this.get('childViews')[0];
// SlidesView has carouselView and another view as it's child, hence this.get('childViews')[0] is carouselView
var newCard = carouselView.createChildView(App.SlideView.extend());
carouselView.get('childViews').pushObject(newCard);
}
}
The above piece of code sucks and hurts me bad. I want to basically add a new SlideView to my CarouselView collection programmatically upon a button trigger. But apparently Ember recommends that childViews should not be manipulated directly and I ought to instead change the underlying content.
It states in my console.log that manipulating childViews is deprecated etc.
So essentially I need to add something to my content to my SlidesController content ? However, I don't want to add something to the content, this is just a soft add, that is providing the user with a slide so that he may choose to edit or add something if he wants to. He can always discard it. A hard add that will require me to persist the new slide to the DB will come once the user decides to save this information.
I have a ViewModel which contains a Boolean property which tells you if the user has authenticated or not.
I have a WrapPanel which is bound to a collection of profiles. The DataTemplate for these profiles has an icon - a closed padlock for when the user is not authenticated and an open one for when the user is authenticated. Ideally these would be bound to the Boolean on the ViewModel but the DataContext for the templates is the individual profile objects.
I have tried,
Setting the Source selector in the binding as specified here although it appear Windows Phone 7 does not support x:Reference
I tried also the Inversion of Control(?) method detailed here (but containerLocator was not found on my object)
I tried applying a Style.Trigger but these are not supported in Windows Phone 7
I also tried accessing the XAML elements in the code behind and updating programmatically on event triggers, however I could not get a handle on the Image element inside the DataTemplate
Edit after comment: WP7 does not support style triggers. But if anyone is looking for this answer on following versions I let the reply below:
I would use a Style Trigger as seen here to update the icon Source property on the fly - as part of the style of your DataTemplate so you would get a hold of your Image.
One way I found that works based on an answer by Damian Antonowicz but does not implement the full inversion of control method that he uses, is as follows,
Create a partial class which resolves to your view-model instance under your view-model namespace, e.g.
public partial class ViewModelInstanceLocator
{
public AppViewModel AppViewModel // Or whatever the type of your view-model is ...
{
get
{
return App.VM; // Or wherever your view model instance is ...
}
}
}
Define the other half of the class in your XAML page as a resource so that it can be referred to as a static resource, I did this in my App.xaml so that it could be referred to everywhere,
<ResourceDictionary>
<viewmodel:ViewModelInstanceLocator x:Key="ViewModelInstanceLocator" />
...
</ResourceDictionary>
You may need to include the relevant namespace if there is not already a reference to your view-model namespace e.g. at the top,
xmlns:viewmodel="clr-namespace:MyAppNamespace.ViewModel"
Finally to bind to the view-model as follows,
{Binding AppViewModel.SomeProperty, Source={StaticResource ViewModelInstanceLocator}}
The binding updates as usual just as if the view-model instance had been referred to through the DataContext. However, it does not work with design-time data.
I'm working on a ASP.NET MVC 3 application, but I'm rather new to MVC in general.
I have a partial view in a my application layout view that needs to have data passed to it. this will appear on every page. Is there a way to make this happen so I don't have to load that data into the view model for every action in the entire site?
As in, if a user navigates to Mysite/admin/settings, I would like to have the partial view on the layout be able to somehow receive the data that it needs without me needing to put that code in the Settings action in the Admin controller.
On this same note, how do you pass data to the layout view of an application anyway?
In these situations I usually use a base ViewModel for my Views
public class ApplicationViewModel
{
public string UserName {get; set;}
....
}
public class SettingsViewModel : ApplicationViewModel
{
}
all your views would inherit from that ViewModel. Your layout would expect it as well
_layout.cshtml:
#model ApplicationViewModel
....
<h1>hello #Model.UserName</h1>
hopefully this answers your question
Partial only renders a view. You need to provide the model manually.
You can create an action for the view you want and render it with Html.Action( actionName ).
Make an action for example menu which will create a model that will be provided to the menu view.
Now you can call the #Html.Action("menu") from wherever, and it will be rendered autonomously. (you can ofcourse provide a controller name as well, and even custom routeData)
You might also want to set Layout = null; in the view to avoid using the master layout of the whole site.
This is how I pass a value to the partial view from my layout page:
Layout page code:
Html.RenderPartial("_SubMenuLeft", new ViewDataDictionary { {"category", "MMG"} });
and in my _SubMenuLeft.cshtml (partial view)
#if (ViewData["category"] == "MMG")
{
...
}
Hope it helps someone for future reference.
I'm looking for the best practice on how to pass data from page to page.
In Page A I have a button that fires off Page B.
On Page B I have 6 textboxes that allow the user to enter information.
When the user is done, the click on a button that brings them back to Page A.
I want to pass that data back to Page A.
I've seen suggestions to:
build XML documents and save to Isolated Storage
use the App class to store information in properties
pass it like a query string
I'm looking for the Best practice. Is there one that Microsoft recommends or one that is generally accepted as the best way?
Thanks
PhoneApplicationService.Current.State["yourparam"] = param
NavigationService.Navigate(new Uri("/view/Page.xaml", UriKind.Relative));
then in other page simply
var k = PhoneApplicationService.Current.State["yourparam"];
Personally I'd store the values entered on Page B in a model(object) that is also accessible to Page A.
Depending on how you're navigating to Page A the second time, one or more of the following may be usful to help understand passing values between pages:
How to pass the image value in one xaml page to another xaml page in windows phone 7?
Passing a complex object to a page while navigating in a WP7 Silverlight application
How to pass an object from a xaml page to another?
How to pass a value between Silverlight pages for WP7?
How do I navigate from one xaml page to another, and pass values?
One thing you can consider is to use MVC: let your App be the controller, store all data in the model, and the pages are just views that contains pure UI logic. In this case your pages are painters and you pass your model object around. This gives nice isolation of business logic and the UI so that you can rev them easily.
BTW, Silverlight and XAML are great tools for MVC so it's a natural match.
There's a couple of things at play here. First of all, if/when the user uses the Back button to return to page A instead of your button, is the information in the text boxes exchanged or not (is Back = Cancel, or is Back = OK?)
That said, if you're using NavigationService.GoBack (which you should be instead of NavigationService.Navigate, because if you use the Navigate call, repeated hits of the back key will cause all kinds of bad UX for your users), then QueryStrings are not an option. Because pages really have no way to reference each other in the WP7 Silverlight nav system, you need to use a 3rd party to hold your data. For that, you can turn to (a) Isolated Storage (slow & heavy, but fail-safe), (b) Use the PhoneApplicationService.State dictionary, or (c) use Global properties of some kind, either hung off of the application object, or using Statics/Singletons...
Remember to watch for Tombstoning behavior when you do this - your page will process the OnNavigatedTo method when (a) you navigate into it in your application (b) you navigate back to it when you complete your work on Page B, or (c) you tombstone your app from that page and return to your application using the Back key.
Sorry I didn't give a more direct answer there - a lot depends on your specific circumstances. In the most general case, I'd strongly consider using the App State Dictionary on the PhoneApplicationService...it is lightweight, easy to use, and survives tombstoning. Just be sure that your keys are as unique as they need to be.
If you create a new Windows Phone project and use the Windows Phone Databound Template you will have most of the work done for you.
What you will want to do is set up the ViewModel to contain all the data for your app. You can serialize and deserialize this data using IsolatedStorage so that it's saved across application sessions and when Tombstoning.
In the template you will notice MailViewModel and ItemViewModel. MainViewModel stores all the data your application needs including an ObservableCollection of ItemViewModel, and ItemViewModel represents the individual data type for your application.
On the DetailsPage.xaml page you'll want to DataBind each textbox to the App.MainViewModel Items. Set the binding to TwoWay if you want the ViewModel to get updated as soon as the user manipulates the data on DetailsPage.xaml. You can optionally set the Binding to OneWay and then have an OK button that writes the changes back to the ViewModel and saves to IsolatedStorage.
Here is an example of what a Binding looks like:
<TextBlock x:Name="ListTitle" Text="{Binding LineOne}" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/>
In this case LineOne is a property in ItemViewModel and the page gets this data from the query string when the user selects an item from the MainPage.xaml. The DataContext for the page determs where the databound information comes from.
Here is the snippet where the MainPage passes the selected item from the ViewModel to the DetailsPage.
// Handle selection changed on ListBox
private void MainListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
// If selected index is -1 (no selection) do nothing
if (MainListBox.SelectedIndex == -1)
return;
// Navigate to the new page
NavigationService.Navigate(new Uri("/DetailsPage.xaml?selectedItem=" + MainListBox.SelectedIndex, UriKind.Relative));
// Reset selected index to -1 (no selection)
MainListBox.SelectedIndex = -1;
}
Here is how the DetailsPage gets the selected item.
protected override void OnNavigatedTo(NavigationEventArgs e)
{
string selectedIndex = "";
if (NavigationContext.QueryString.TryGetValue("selectedItem", out selectedIndex))
{
int index = int.Parse(selectedIndex);
DataContext = App.ViewModel.Items[index];
}
}
Play around with the default template above and ask any additional questions.
The beauty of databinding and the ObservableCollection is that you can just update the data and the UX will reflect those changes immediatley. This is because any changes to the data fires off an event:
public string LineOne
{
get
{
return _lineOne;
}
set
{
if (value != _lineOne)
{
_lineOne = value;
NotifyPropertyChanged("LineOne");
}
}
}
NotifyPropertyChanged() that broadcasts this information to the View.
You can also keep it simple and use PhoneApplicationService.Current.State which is basically a hashtable. You will need to implement your own marshalling to and from isolated storage if you want anything to outlive the app.
Omar's suggestion to use the Windows Phone Databound Template is probably the best idea on this page. It amounts to the same as my suggestion but you will get a better result (more maintainable code) at the cost of a longer steeper learning curve.
I suggest you do it my way and then do it again Omar's way.
as i implemented like this.. Whether its correct or not i dont know..
When u click news list page it should open the news detail page.
I want to pass the selected news item contents from news List-Page to news-details Page.
the News list page contains following method.
protected override void OnNavigatedFrom(System.Windows.Navigation.NavigationEventArgs e)
{
NewsDetailsPage newsDetailPage = (e.Content as NewsDetailsPage);
if (newsDetailPage != null)
newsDetailPage.SelectedNewsItem = SelectedNewsItem; //Contains the news details
base.OnNavigatedFrom(e);
}
In the News details Page. U can access that(SelectedNewsItem) object.
This may or may not be correct.
One option is to use Application.Resources:
Store data:
Application.Current.Resources.Add("NavigationParam", customers);
NavigationService.Navigate(new Uri("/Page2.xaml", UriKind.Relative));
Retrieve data:
var customers = (List<Customer>) Application.Current.Resources["NavigationParam"];
Here's a blog post with describes this in more detail: http://mikaelkoskinen.net/windows-phone-pass-data-between-pages-application-resources/ (author: me)