Capture checkbox event in the recyclerview - xamarin

Question

I have MainViewModel where it shows all the person as a list using recyclerview. Each person has age, gender, name property and also checkbox in order to delete it.
I could not able to figure out how I could able to capture user checkbox event in the MainViewModel?
MainView.axml
<CheckBox
android:id="#+id/checkbox"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
local:MvxBind="Checked IsAllSelected" />
<TextView
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content"
android:text="Name"
android:layout_weight="1" />
<TextView
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content"
android:text="Age" />
<TextView
android:layout_width="0dp"
android:layout_weight="1"
android:layout_height="wrap_content"
android:text="Gender" />
</LinearLayout>
<MvxRecyclerView
android:id="#+id/personRecyclerView"
android:scrollbars="vertical"
android:layout_width="match_parent"
android:layout_height="0dp"
local:MvxItemTemplate="#layout/persontemplate"
local:MvxBind="ItemsSource Items; ItemClick ItemSelected" />
</LinearLayout>
PersonTemplate.axml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:local="http://schemas.android.com/apk/res-auto"
android:orientation="horizontal"
android:layout_width="match_parent"
android:gravity="center_vertical"
android:layout_height="60dp">
<CheckBox
android:id="#+id/chked"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
local:MvxBind="Checked IsSelected; Click CheckBoxSelectionCommand;" />
<TextView
android:id="#+id/Name"
android:layout_width="0dp"
android:layout_height="wrap_content"
local:MvxBind="Text Name"
android:layout_weight="1" />
<TextView
android:id="#+id/Age"
android:layout_width="0dp"
android:layout_height="wrap_content"
local:MvxBind="Text Age"
android:layout_weight="1" />
<TextView
android:id="#+id/Gender"
android:layout_width="0dp"
android:layout_height="wrap_content"
local:MvxBind="Text Gender
android:layout_weight="1" />
</LinearLayout>
I am trying to update IsDeleteBtnShow based on the checkbox selection for each item.
MainViewModel.cs
public bool IsAllSelected
{
get { return _isAllSelected; }
set
{
_isAllSelected= value;
Items.ForEach(x => x.IsSelected = _isAllSelected);
IsDeleteBtnShow = _isAllSelected;
RaisePropertyChanged(() => IsAllSelected);
}
}
I have the following viewmodel which is used by RecyclerView to tabulate person as a list.
PersonRecyclerViewModel.cs
public bool IsSelected
{
get { return _isSelected; }
set
{
_isSelected = value;
RaisePropertyChanged(() => IsSelected);
}
}
public ICommand CheckBoxSelectionCommand
{
get
{
return new MvxCommand(() =>
{
var isChecked = IsSelected;
});
}
}
public static PersonViewModel CreateViewModel(Person person)
{
return new PersonViewModel
{
IsSelected = person.IsSelected,
Age= person.Age,
Gender= person.Gender,
Name= entity.Name,
};
}

Answer 1

You can just pass a callback or command to the cration of the ItemViewModel. CreateViewModel(Person person, Action<PersonViewModel> checkboxSelectedCallback) and use it directly as or in CheckBoxSelectionCommand. Something like this:
CheckBoxSelectionCommand
public ICommand CheckBoxSelectionCommand
{
get
{
return new MvxCommand(() =>
{
var isChecked = IsSelected;
ParentCheckBoxSelectionCallback(this);
});
}
}
CreateViewModel
public static PersonViewModel CreateViewModel(Person person, Action<PersonViewModel> checkboxSelectedCallback)
{
return new PersonViewModel
{
IsSelected = entity.IsSelected,
Age = entity.Age,
ParentCheckBoxSelectionCallback = checkboxSelectedCallback,
Gender= entity.Gender,
Name= entity.Name,
};
}
MainViewModel
// only create once.
_checkedChangedCallback = (person =>
{
// do what you have to do if a item got selected
});
// where you create persons
CreateViewModel(person, _checkedChangedCallback );

Answer 2

Another way to do this without adding Actions or any logic in your model is to make your model implement INotifyPropertyChanged:
class PersonRecyclerViewModel : INotifyPropertyChanged
The quickest way to do it is using Fody PropertyChanged because you´ll get the whole implementation of the interface by just adding an attribute to the model:
[ImplementPropertyChanged]
class PersonRecyclerViewModel {}
In your ViewModel, when you get or refresh data source, a for loop would listen for item property changes:
foreach(var item in Items)
{
var n = (INotifyPropertyChanged)item;
n.PropertyChanged += OnItemPropertyChanged;
}
private void OnItemPropertyChanged(object sender, PropertyChangedEventArgs propertyChangedEventArgs)
{
if(propertyChangedEventArgs.PropertyName == "IsSelected")
{
// do whatever you need here
}
}