need some help, when i click the tap_event I get a message box delete or cancel which works and the price is taken off the total but it does'nt update the shopping cart after, it crashes on "ListBoxCart.Items.Remove(curr), thanks in advance!
private void listBoxCart_Tap(object sender, GestureEventArgs e)
{
if (MessageBox.Show("Are you sure!", "Delete", MessageBoxButton.OKCancel)
== MessageBoxResult.OK)
{
foreach (Dvd curr in thisapp.ShoppingCart)
{
if (curr.Equals(listBoxCart.SelectedItem))
{
listBoxCart.Items.Remove(curr);
listBoxCart.SelectedIndex = -1;
total -= Convert.ToDecimal(curr.price);
NavigationService.Navigate(new Uri("/ShoppingCart.xaml", UriKind.RelativeOrAbsolute));
}
}
txtBoxTotal.Text = total.ToString();
listBoxCart.ItemsSource = thisapp.ShoppingCart;
}
else
{
NavigationService.Navigate(new Uri("/ShoppingCart.xaml", UriKind.RelativeOrAbsolute));
}
}
I have wrote an artile (sorry in french but you can read the XAML) : http://www.peug.net/2012/05/17/contextmenu-dans-listbox-datatemplate/
and in the code-behind : an example :
private void MenuItem_Click(object sender, RoutedEventArgs e)
{
var menuItem = sender as MenuItem;
var fe = VisualTreeHelper.GetParent(menuItem) as FrameworkElement;
Dvd _fig = fe.DataContext as Dvd;
thisapp.ShoppingCart.Remove(_fig);
reloading();
}
When you set the ItemsSource property for the ListBox, it generates a read-only collection and displays them. What you're trying to do is access this read-only collection and modify it but because it's read-only, you can't do that.
Instead you can either have your collection implement the INotifyCollectionChanged interface and raise a collection changed event when the user has deleted the item or use an ObservableCollection instead to store your items. ObservableCollection implements the INotifyCollectionChanged interface for you so you can remove items from the ObservableCollection and the changes will reflect in the Listbox automatically.
ObservableCollection also implements INotifyPropertyChanged so any property updates will also be updated in the ListBox.
Related
I have some property which I am using from Page2 in HomePageViewModel, When I navigate to Page2 I have changed that property and on coming back by doing NavigiationPop.
HomePage is not re-loaded/ refreshed at all as I have set the BindingContext in the constructor of HomePage, which is loaded only once.
The solution which is working for me is
Setting the BindingContext to the ViewModel on "onAppearing()", usually its not consider the best practice. But I also need to refresh the values which I have changed on Page2.
Looking forward for your valuable inputs and suggestions.
Also Pros/Cons of Setting the BindingContext in OnAppearing.
Thanks,
Hemant
It depends on you, they all can achieve the effect.
However if you want to reduce the CPU consumption of the program, then don't use the onAppearing method too much to refresh the page data.
Another method is that you can change the data of the model through Delegate/Event/MessageCenter.
You can refer to this discussion to know how to use Delegate/Event/MessageCenter.
Here I will give the sample by using MessageCenter to achieve that.
For example, the TestViewModel as follows:
public class TestViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
private string pagetitle;
public string PageTitle
{
get
{
return pagetitle;
}
set
{
if (pagetitle != value)
{
pagetitle = value;
NotifyPropertyChanged();
}
}
}
}
Then bind it in FirstPage as follows, and Subscribe MessageCenter inside it:
TestViewModel testViewModel = new TestViewModel();
BindingContext = testViewModel;
MessagingCenter.Subscribe<object>(this, "Hi", (sender) =>
{
// Do something whenever the "Hi" message is received
testViewModel.PageTitle = "Modified Title";
});
Then in the SecondPage, when changing the data by sending message. When back to FirstPage, the View Will be updated.
private void Button_Clicked(object sender, EventArgs e)
{
MessagingCenter.Send<object>(this, "Hi");
}
I have to implement autofill service for iOS in Xamarin forms, Is there any sample code ? How we can achieve it?
You can use package dotMorten.Xamarin.Forms.AutoSuggestBox from nuget .
Usage
xaml
<AutoSuggestBox PlaceholderText="Search" WidthRequest="200"
TextChanged="AutoSuggestBox_TextChanged"
QuerySubmitted="AutoSuggestBox_QuerySubmitted"
SuggestionChosen="AutoSuggestBox_SuggestionChosen"/>
Code Behind
private void AutoSuggestBox_TextChanged(AutoSuggestBox sender, AutoSuggestBoxTextChangedEventArgs args)
{
// Only get results when it was a user typing,
// otherwise assume the value got filled in by TextMemberPath
// or the handler for SuggestionChosen.
if (args.Reason == AutoSuggestionBoxTextChangeReason.UserInput)
{
//Set the ItemsSource to be your filtered dataset
//sender.ItemsSource = dataset;
}
}
private void AutoSuggestBox_SuggestionChosen(AutoSuggestBox sender, AutoSuggestBoxSuggestionChosenEventArgs args)
{
// Set sender.Text. You can use args.SelectedItem to build your text string.
}
private void AutoSuggestBox_QuerySubmitted(AutoSuggestBox sender, AutoSuggestBoxQuerySubmittedEventArgs args)
{
if (args.ChosenSuggestion != null)
{
// User selected an item from the suggestion list, take an action on it here.
}
else
{
// User hit Enter from the search box. Use args.QueryText to determine what to do.
}
}
For more details you can check https://github.com/dotMorten/XamarinFormsControls/tree/master/AutoSuggestBox
Is is possible to get an event when an item in the collection bound to a Xamarin Forms listview changes?
For example my object has a Date field which is bound to a label in a ViewCell. I would like an event fired when the Date is changed. Our object implements INotifyPropertyChanged so the listview updates properly.
I can manually subscribe to the OnPropertyChanged event of each item but I'm hoping their is an easier way.
Thanks.
There are triggers in Xamarin.Forms. It seems like an event trigger will do what you need. For example:
<EventTrigger Event="TextChanged">
<local:NumericValidationTriggerAction />
</EventTrigger>
public class NumericValidationTriggerAction : TriggerAction<Entry>
{
protected override void Invoke (Entry entry)
{
double result;
bool isValid = Double.TryParse (entry.Text, out result);
entry.TextColor = isValid ? Color.Default : Color.Red;
}
}
You can find more information about triggers here
See this example for deleting an object when it is selected from a list view.
private MyItemsViewModel _myItemsViewModel;
private void MyItemsListView_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
MyItem item = (MyItem)e.SelectedItem;
if (item == null)
return;
// remove the item from the ObservableCollection
_myItemsViewModel.Items.Remove(item);
}
I'm using this tutorial as a base for my first app. I'm trying to select a listbox item and view data from said item, but(my Android and iOS brain is having issues with this), how do I view the data binding behind that?
lstContact.ItemsSource = from contact in xmlContact.Descendants("contact")
select new ContactItem
{
ImageSource = contact.Element("Image").Value,
FName = contact.Element("FName").Value,
LName = contact.Element("LName").Value
Extension = contact.Element("Extension").Value,
Email = contact.Element("Email").Value,
ID = contact.Element("ID").Value
};
This is how I'm setting it up my data source, and it's pulling correctly. How would I go about going in and getting the email or extension from said listbox item?
In your example, lstContact.ItemsSource is effectively now a IEnumerable<ContactItem>. Assuming you want a 'selected' item, in your SelectionChanged event:
public void ListBoxContainerSelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (lstContact.SelectedIndex == -1) return;
ContactItem contactItem = (ContactItem)lstContact.SelectedItem;
/*do something */
lstContact.SelectedIndex = -1;
}
I have a simple user control in Windows Phone 7 and I want to get access to the querystring collection from the user controls Constructor. I have tried many ways and cannot seem to get acess to the containing XAML's querystring collection.
Essentially I am navigating to the page and the my user control is going to access the querystring value to write the value back to the interface.
Am I missing adding an assembly or reference or something?
I am not sure you should be trying to get at the information from the page's constructor, as it won't necessairly get called every time you land on this page. A better approach is to override the OnNavigatedTo method inherited from PhoneApplicationPage. Looking a little more carefully at your question, you may be trying to do this within a control embedded in the page, in which case you need to get at the Page in order to obtain the navigation information.
Regardless, the NavigationContext property from the page has a QueryString parameter that you can use to access the information you're after.
The following example assumes I have a parameter named "Message" in the query string when navigating to this page:
public partial class MyPage : PhoneApplicationPage
{
// Constructor
public MyPage()
{
InitializeComponent();
}
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
base.OnNavigatedTo(e);
String navigationMessage;
if (NavigationContext.QueryString.TryGetValue("Message", out navigationMessage))
{
this.textBlock1.Text = navigationMessage;
}
}
}
Sorry about that - I started to get there, and thanks for the clarification. Your best bet then is to walk up the visual tree from your control to find the Page, then you can have at the NavigationContext. In my sample below, I have a button on a custom control within the page, whose click event finds the nav context and looks for a certain navigation parameter - I couldn't tell from the question or your follow-up what would drive the control to "want" to find the content of the query string.
(Note about getting info from the ctor follows the code below)
public partial class WindowsPhoneControl1 : UserControl
{
public WindowsPhoneControl1()
{
InitializeComponent();
}
private void button1_Click(object sender, RoutedEventArgs e)
{
GetTheQueryString();
}
private void GetTheQueryString()
{
var result = "No Joy";
var page = FindRootPage(this);
if (page != null)
{
if (page.NavigationContext.QueryString.ContainsKey("Param"))
{
result = page.NavigationContext.QueryString["Param"];
}
}
queryStringText.Text = result;
}
private static PhoneApplicationPage FindRootPage(FrameworkElement item)
{
if (item != null && !(item is PhoneApplicationPage))
{
item = FindRootPage(item.Parent as FrameworkElement);
}
return item as PhoneApplicationPage;
}
}
Note that this won't work from the ctor because of how Xaml works...the Xml tag drives the ctor to be called, then properties are set as indicated, then it is added as a child/item/etc in its container. If you do need to get at the context ASAP using this "walk up the tree" technique, handle the Control's Loaded event, by which time the control does have a parent and a tree that can be walked...
public WindowsPhoneControl1()
{
InitializeComponent();
Loaded += WindowsPhoneControl1_Loaded;
}
private void WindowsPhoneControl1_Loaded(Object sender, RoutedEventArgs e)
{
GetTheQueryString();
}
I would add a property to the UserControl subclass that would be set by the page in its OnNavigatedTo() method.