I am working on xamarin.forms and want to start an animation when the image source are changed.
<ListView >
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Image Source="{Binding FavoriteImage}" x:Name="favoriteImage">
<Image.GestureRecognizers>
TapGestureRecognizer Command="{Binding Source={x:Reference CurrentPage},Path=BindingContext.ClickLikedCommand}" CommandParameter="{Binding .}" NumberOfTapsRequired="1"/>
</Image.GestureRecognizers>
</Image>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
The image source is bind to an variable in the ViewModel and will be changed if user click the image and get a successful response from server. Then the new Image will be shown with some custom animation, so where can I trigger this animation since the image source changed?
I have read the "Behavior" and "Trigger" tutorial online, It seems it could trigger an animation by an event, but Image class has not such an "SourceChanged" event.
You can use the OnPropertyChanged method:
public class ExImage : Image
{
protected override void OnPropertyChanged(string propertyName = null)
{
base.OnPropertyChanged(propertyName);
if (propertyName == nameof(Source))
Device.BeginInvokeOnMainThread(async () =>
{
await this.ScaleTo(1.2);
await this.ScaleTo(1);
});
}
}
Related
After Zooming the image in CarouselView and swiping the image to other image and coming back to that image which i had zoomed the image is already zoomed, as i want the image should come to its original form when i swipe to other image.
Here is my below XMAl code:-
<cards:CarouselView Grid.Row="1" PositionChanged="ImageCollection_PositionChanged" CurrentItemChanged="ImageCollection_CurrentItemChanged_1" IndicatorView="{x:Reference imageIndicator}" x:Name="ImageCollection">
<cards:CarouselView.ItemTemplate>
<DataTemplate>
<ContentView>
<Grid Padding="0" Margin="0">
<pinch:PinchZoom>
<pinch:PinchZoom.Content>
<Image Source="{Binding image}" x:Name="ImageData" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" Aspect="AspectFill">
</Image>
</pinch:PinchZoom.Content>
</pinch:PinchZoom>
</Grid>
</ContentView>
</DataTemplate>
</cards:CarouselView.ItemTemplate>
</cards:CarouselView>
You can refer to the following code. When you click the button, the image will display original size. You can add the code of Button_Clicked to PositionChanged or CurrentItemChanged:
MainPage.xaml:
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="Forms_CarouseIView.MainPage"
xmlns:local="clr-namespace:Forms_CarouseIView;assembly=Forms_CarouseIView">
<ContentPage.Content>
<StackLayout Padding="20"
x:Name="stacklayout">
<local:PinchToZoomContainer x:Name="PinchToZoomContainer">
<local:PinchToZoomContainer.Content >
<Image Source="ddd.png"/>
</local:PinchToZoomContainer.Content>
</local:PinchToZoomContainer>
<Button Text="reset" Clicked="Button_Clicked"/>
</StackLayout>
</ContentPage.Content>
</ContentPage>
MainPage.xaml.cs:
namespace Forms_CarouseIView
{
public partial class MainPage : ContentPage
{
public static double scale1;
public static double tx;
public static double ty;
public MainPage()
{
InitializeComponent();
}
private void Button_Clicked(object sender, EventArgs e)
{
PinchToZoomContainer.Content.Scale=scale1;
PinchToZoomContainer.TranslationX=tx;
PinchToZoomContainer.TranslationY=ty;
}
}
}
PinchToZoomContainer.cs:
namespace Forms_CarouseIView
{
public class PinchToZoomContainer : ContentView
{
...
void OnPinchUpdated(object sender, PinchGestureUpdatedEventArgs e)
{
if (e.Status == GestureStatus.Started)
{
...
MainPage.scale1 = Content.Scale;
}
if (e.Status == GestureStatus.Running)
{
...
}
if (e.Status == GestureStatus.Completed)
{
...
MainPage.tx = -xOffset;
MainPage.ty = -yOffset;
}
}
}
}
For more code about PinchToZoomContainer.cs, you can refer to Creating a PinchToZoom container by official.
I'm trying to make a custom home page where pages are listed on an Horizontal scroll view as "Services" so each one of them should navigate to a different Page.
I have a view like this:
<controls:HorizontalScrollView HeightRequest="160"
Orientation="Horizontal"
ItemsSource="{Binding OwnerServicesList}"
x:Name="OwnerServicesSlider"
ItemSelected="OwnerServicesSlider_ItemSelected">
<controls:HorizontalScrollView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Margin="10,0,5,0" WidthRequest="100" HeightRequest="100">
<Image HorizontalOptions="Start" Source="{Binding ImgUrl}" WidthRequest="100" HeightRequest="100" />
<Label Style="{StaticResource BoldLabel}" HorizontalTextAlignment="Center" FontSize="13" LineBreakMode="TailTruncation" Text="{Binding Name}" TextColor="Black"/>
</StackLayout>
</ViewCell>
</DataTemplate>
Im using a custom made controller for a Horizontal Scroll view that works like a listview, every item on tap raises a ItemTappedEventArgs event.
Inside my model i´ve declared a public Page Page { get; set; } for each object in the scroll view.
What im trying to do is recover the tapped element and recover the Page stored in it so that I can Navigate to that specific page.
So far I have something like this:
private void OwnerServicesSlider_ItemSelected(object sender, ItemTappedEventArgs e)
{
var service = OwnerServicesSlider.SelectedItem as Services;
Navigation.PushAsync(service.Page);
}
It shows no errors but when I run it I get a
InvalidOperationException: 'Page must not already have a parent.
Any hint will be appreciated!
as Jason said,maybe the page you would push which is exist in thecurren navigation structure,there is a workaround ,before you push the page :
private void OwnerServicesSlider_ItemSelected(object sender, ItemTappedEventArgs e)
{
var service = OwnerServicesSlider.SelectedItem as Services;
service.Page.Parent = null;
Navigation.PushAsync(service.Page);
}
When I'm writing my Button, which is inherited from the button, I set the ControlTemplate using an image, the source is x:bind to a string property in code-behind, like the screenshot below:
<Grid x:Name="rectangle1">
<Image Source="{x:Bind aCheckImage}" //Error Here
Stretch="UniformToFill"
HorizontalAlignment="Center"
VerticalAlignment="Center">
</Image>
</Grid>
Why it throws an error that is "Object reference not set to an instance of an object" in compile. How to fix it?
#Vijay Nirmal gives me a way to solve it.
If you want to bind the image source to other value that you should sure your value in the code. I will write it below.
public static readonly DependencyProperty aCheckImageProperty = DependencyProperty.Register(
"aCheckImage", typeof(BitmapSource), typeof(MainPage), new PropertyMetadata(default(BitmapSource)));
public BitmapSource aCheckImage
{
get { return (BitmapSource) GetValue(aCheckImageProperty); }
set { SetValue(aCheckImageProperty, value); }
}
I should set it in constructor.
public MainPage()
{
InitializeComponent();
aCheckImage = new BitmapImage(new Uri("ms-appx:///Assets/LockScreenLogo.scale-200.png"));
}
If you want to know how to write uri, please see https://msdn.microsoft.com/zh-cn/library/windows/apps/xaml/hh965322(v=win.10).aspx
And then I can bind it in XAML.
<Grid x:Name="rectangle1">
<Image Source="{x:Bind aCheckImage}"
Stretch="UniformToFill"
HorizontalAlignment="Center"
VerticalAlignment="Center">
</Image>
</Grid>
Update: Just a reminder, there's a 500 point bonus on this if someone can just show me how to implement this functionality without using Gestures>
I am using a ViewCell and a gesture recognizer to open up a picker with the following code. The ViewCell has a label on the left and a label area on the right that is populated initially when the app starts and later with the picker when the ViewCell is clicked.
XAML
<ViewCell x:Name="ati" Tapped="OpenPickerCommand">
<Grid VerticalOptions="CenterAndExpand" Padding="20, 0">
<Grid.GestureRecognizers>
<TapGestureRecognizer
Command="{Binding OpenPickerCommand}"
CommandParameter="{x:Reference atiPicker}" NumberOfTapsRequired="1" />
</Grid.GestureRecognizers>
<local:LabelBodyRendererClass Text="Answer Time Interval" HorizontalOptions="StartAndExpand" />
<Picker x:Name="atiPicker" IsVisible="false" HorizontalOptions="End" SelectedIndexChanged="atiPickerSelectedIndexChanged" ItemsSource="{Binding Times}"></Picker>
<local:LabelBodyRendererClass x:Name="atiLabel" HorizontalOptions="End"/>
</Grid>
</ViewCell>
<ViewCell x:Name="pti" Tapped="OpenPickerCommand">
<Grid VerticalOptions="CenterAndExpand" Padding="20, 0">
<Grid.GestureRecognizers>
<TapGestureRecognizer
Command="{Binding OpenPickerCommand}"
CommandParameter="{x:Reference ptiPicker}" NumberOfTapsRequired="1" />
</Grid.GestureRecognizers>
<local:LabelBodyRendererClass Text="Phrase Time Interval" HorizontalOptions="StartAndExpand" />
<Picker x:Name="ptiPicker" IsVisible="false" HorizontalOptions="End" SelectedIndexChanged="ptiPickerSelectedIndexChanged" ItemsSource="{Binding Times}"></Picker>
<local:LabelBodyRendererClass x:Name="ptiLabel" HorizontalOptions="End"/>
</Grid>
</ViewCell>
C# This works for different pickers (ati, bti, pti etc) with CommandParameter
public SettingsPage()
{
InitializeComponent();
BindingContext = new CommandViewModel();
}
void atiPickerSelectedIndexChanged(object sender, EventArgs e)
{
var picker = (Picker)sender;
int selectedIndex = picker.SelectedIndex;
if (selectedIndex != -1)
{
App.DB.UpdateIntSetting(Settings.Ati, selectedIndex);
atiLabel.Text = AS.ati.Text();
}
}
void ptiPickerSelectedIndexChanged(object sender, EventArgs e)
{
var picker = (Picker)sender;
int selectedIndex = picker.SelectedIndex;
if (selectedIndex != -1)
{
App.DB.UpdateIntSetting(Settings.Pti, selectedIndex);
ptiLabel.Text = AS.pti.Text();
}
}
public class CommandViewModel: ObservableProperty
{
public ICommand openPickerCommand;
public CommandViewModel()
{
openPickerCommand = new Command<Picker>(PickerFocus);
//openPickerCommand = new Command(tapped);
}
public ICommand OpenPickerCommand
{
get { return openPickerCommand; }
}
void PickerFocus(Picker param)
{
param.Focus();
}
}
I would like to remove the use of TapGestureRecognizers but I still want to retain the functionality and layout.
It's been suggested to me that it would be better if I used the Tapped event of the ViewCell like this:
Tapped="OnTapped"
Can someone explain in some detail how I could wire this up in C#. Would I be best to code something into the CommandViewModel as well as in the C# backing code. Also can the view model have one method that takes an argument so it could be used to open up different pickers?
An example of how I could do this would be very much appreciated. Note that I don't particularly need to use the CommandViewModel if there is a way that I could do this by coding just in the .cs backing code.
(Sorry for the poor english)
Despite not being best practice, I guess you can do something like this, dismissing the viewmodel:
XAML:
<ViewCell x:Name="ati" Tapped="OpenPickerCommand">
<Grid VerticalOptions="CenterAndExpand" Padding="20, 0">
<local:LabelBodyRendererClass Text="Answer Time Interval" HorizontalOptions="StartAndExpand" />
<Picker x:Name="atiPicker"
IsVisible="false"
HorizontalOptions="End"
SelectedIndexChanged="atiPickerSelectedIndexChanged"
ItemsSource="{Binding Times}">
</Picker>
<local:LabelBodyRendererClass x:Name="atiLabel" HorizontalOptions="End"/>
</Grid>
</ViewCell>
<ViewCell x:Name="pti" Tapped="OpenPickerCommand">
<Grid VerticalOptions="CenterAndExpand" Padding="20, 0">
<local:LabelBodyRendererClass Text="Phrase Time Interval" HorizontalOptions="StartAndExpand" />
<Picker x:Name="ptiPicker" IsVisible="false" HorizontalOptions="End" SelectedIndexChanged="ptiPickerSelectedIndexChanged" ItemsSource="{Binding Times}"></Picker>
<local:LabelBodyRendererClass x:Name="ptiLabel" HorizontalOptions="End"/>
</Grid>
</ViewCell>
C#:
private void OpenPickerCommand(object sender, System.EventArgs e)
{
if (sender != null)
{
Picker pkr = sender == ati ? atiPicker : ptiPicker;
pkr.Focus();
}
}
Answering your question "Can the view model have one method that takes an argument?", it is exactly what you're already doing using the 'OpenPickerCommand' method. The problem is that using the ViewCell's public event 'Tapped', you can't set parameters to the delegate handler.
Let me know if it works for you or if you do need some more information.
I hope it helps.
You can solve this with attached properties. Simply define a "behavior" class for ViewCell that adds the Command/Parameter properties.
public static class TappedCommandViewCell
{
private const string TappedCommand = "TappedCommand";
private const string TappedCommandParameter = "TappedCommandParameter";
public static readonly BindableProperty TappedCommandProperty =
BindableProperty.CreateAttached(
TappedCommand,
typeof(ICommand),
typeof(TappedCommandViewCell),
default(ICommand),
BindingMode.OneWay,
null,
PropertyChanged);
public static readonly BindableProperty TappedCommandParameterProperty =
BindableProperty.CreateAttached(
TappedCommandParameter,
typeof(object),
typeof(TappedCommandViewCell),
default(object),
BindingMode.OneWay,
null);
private static void PropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
if (bindable is ViewCell cell)
{
cell.Tapped -= ViewCellOnTapped;
cell.Tapped += ViewCellOnTapped;
}
}
private static void ViewCellOnTapped(object sender, EventArgs e)
{
if (sender is ViewCell cell && cell.IsEnabled)
{
var command = GetTappedCommand(cell);
var parameter = GetTappedCommandParameter(cell);
if (command != null && command.CanExecute(parameter))
{
command.Execute(parameter);
}
}
}
public static ICommand GetTappedCommand(BindableObject bindableObject) =>
(ICommand)bindableObject.GetValue(TappedCommandProperty);
public static void SetTappedCommand(BindableObject bindableObject, object value) =>
bindableObject.SetValue(TappedCommandProperty, value);
public static object GetTappedCommandParameter(BindableObject bindableObject) =>
bindableObject.GetValue(TappedCommandParameterProperty);
public static void SetTappedCommandParameter(BindableObject bindableObject, object value) =>
bindableObject.SetValue(TappedCommandParameterProperty, value);
}
After that reference your behavior namespace in XAML and specify the property values using fully qualified names:
<ViewCell StyleId="disclosure-indicator"
behaviors:TappedCommandViewCell.TappedCommand="{Binding BrowseCommand}"
behaviors:TappedCommandViewCell.TappedCommandParameter="https://www.google.com">
<StackLayout Orientation="Horizontal">
<Label Text="Recipient"
VerticalOptions="Center"
Margin="20,0"/>
<Label Text="{Binding LedgerRecord.Recipient}"
HorizontalOptions="EndAndExpand"
VerticalOptions="Center"
Margin="0,0,20,0"/>
</Label>
</StackLayout>
</ViewCell>
The above will allow you to use MVVM and no Tap Gesture Recognizers.
The first problem is that you're mixing the code-behind and MVVM
approaches in the same code. It is confusing and certainly not the
right way to code what you want to achieve. So, all commanding must
be in the ViewModel attached to the View, no code-behind apart some
code only used for UI effects.
There is no need to define a gesture recognizer for all visual items since you just want to detect the tap on all the surface of the viewcell. To achieve this you must define all children of the ViewCell with InputTransparent=true. So the tap will not be detected and will be trapped by the parent ViewCell (you
must indicate the InpuTransparent because there is no tap event
bubbling in X.Forms).
Showing and Hidding the picker is a View problem not a ViewModel one. So here you can use some code-behind to create an event handler for the ViewCell Tapped event. This handler will just set visible=true on the picker.
The picker selected event must be connected to a corresponding Command in the ViewModel. So each time the picker is displayed and a value is selected your viewmodel will be aware of the action. This is the only command you need in your viewmodel. Depending of XForms version the picker has no bindable command, so you can use one of the numerous "bindablepicker" implementation you can find on the web or you can also use a XAML EventToCommand Behavior.
So there is two different problems : showing/hidding the picker which can be achieved directly in XAML or with the help of a bit of code-behind; and the picker item selection that must be managed using a Command in the viewmodel.
Hoping this will help you
I have a Listview in Xaml and I need to bind ItemTapped event to my ModelView using MVVM.
My ListView looks like.
<ListView x:Name="list"
ItemsSource="{Binding employeeList}"
ItemTapped= {Binding selectedItem} >
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<ViewCell.View>
</ViewCell.View>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
ItemTapped is an event which, in MVVM, normally corresponds to an ICommand*. If you meant to bind to a normal data property, judging from the attempted binding statement in your XAML snippet, then it would make more sense to do bind ListView's SelectedItem property instead :
<ListView x:Name="list"
ItemsSource="{Binding EmployeeList}"
SelectedItem="{Binding SelectedItem}">
.....
</ListView>
If there is data related action that need to be taken upon ItemTapped event occur, it might instead be implemented on SelectedItem property changed which triggered via binding (as in the XAML binding above) :
private ItemModel _selectedItem;
public ItemModel SelectedItem
{
get { return _selectedItem; }
set
{
if(_selectedItem != value)
{
_selectedItem = value;
OnPropertyChanged();
//this can be placed before or after propertychanged notification raised,
//depending on the situation
DoSomeDataOperation();
}
}
}
*) Xamarin Blog : Turn Events into Commands with Behaviors