How to create select all check box in xamarin form - xamarin.forms

Question

I have create a list view and inside listview template I have multiple check box.
I have a select all check box on before the list view.
Select all and deselect all works fine.
How can uncheck “SelectAll” check box if I uncheck any of the check box present inside list view.

Answer 1

You can try to add new field and bind it to the property IsChecked of CheckBox.
And we can add event handler to the individual CheckBoxes of your ListView, then we can update the binded property of the CheckBox(IsCheckAll).
I created a demo and achieved this function.
You can refer to the following code:
MyViewModel.cs
public class MyViewModel: INotifyPropertyChanged
{
public ObservableCollection<Item> Items { get; set; }
public bool IsUnCheckedOneItem { get; set; } = false;
// add property `IsCheckAll` for the `Select all` checkbox
private bool _isCheckAll;
public bool IsCheckAll
{
get => _isCheckAll;
set
{
SetProperty(ref _isCheckAll, value);
//update all the items
if (!IsUnCheckedOneItem)
{
updateAllItems(IsCheckAll);
IsUnCheckedOneItem = false;
}
}
}
private void updateAllItems(bool ischecked)
{
foreach (var item in Items)
{
item.IsChecked = ischecked;
}
}
public ICommand CheckAllCommand { get; set; }
public ICommand UpdateThisItemCommand { get; set; }
public MyViewModel() {
Items = new ObservableCollection<Item>();
Items.Add( new Item { NumType = "S" , LocationCode = "0001"});
Items.Add(new Item { NumType = "M", LocationCode = "0002" });
Items.Add(new Item { NumType = "L", LocationCode = "0003" });
Items.Add(new Item { NumType = "S", LocationCode = "0001" });
Items.Add(new Item { NumType = "M", LocationCode = "0002" });
Items.Add(new Item { NumType = "L", LocationCode = "0003" });
UpdateThisItemCommand = new Command<Item>(checkboxcommand);
}
private void checkboxcommand(Item obj)
{
if (obj!= null)
{
if (!obj.IsChecked )
{
// you also need to add some other logic codes here
if (IsCheckAll && !CheckAllMethod()) {
IsUnCheckedOneItem = true;
IsCheckAll = false;
}
}
else if (obj.IsChecked && CheckAllMethod()) {
IsCheckAll = true;
}
}
// here
IsUnCheckedOneItem = false;
}
public bool CheckAllMethod()
{
bool ischeckedAll = true;
foreach (var item in Items)
{
if (!item.IsChecked)
{
ischeckedAll = false;
}
}
return ischeckedAll;
}
bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
{
if (Object.Equals(storage, value))
return false;
storage = value;
OnPropertyChanged(propertyName);
return true;
}
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged;
}
Item.cs
public class Item: INotifyPropertyChanged
{ // IsChecked for the checkbox of Item in listview
private bool _isChecked;
public bool IsChecked
{
get => _isChecked;
set
{
SetProperty(ref _isChecked, value);
}
}
public string NumType { get; set; }
public string LocationCode { get; set; }
public string Barcode { get; set; }
public string UserName { get; set; }
public string PickingAdjustementDate { get; set; }
bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
{
if (Object.Equals(storage, value))
return false;
storage = value;
OnPropertyChanged(propertyName);
return true;
}
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged;
}
MainPage.xaml
<ContentPage.BindingContext>
<xamlistviewapp:MyViewModel></xamlistviewapp:MyViewModel>
</ContentPage.BindingContext>
<StackLayout Orientation="Vertical"
Spacing="25"
Padding="30,0"
VerticalOptions="Center"
>
<Label Text="select all items"/>
<CheckBox IsChecked="{Binding IsCheckAll}" >
</CheckBox>
<ListView Grid.Row="1" x:Name="listview" ItemsSource="{Binding Items}" >
<ListView.Header>TheHeader</ListView.Header>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<Grid >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="70"/>
<ColumnDefinition Width="100"/>
<ColumnDefinition Width="80"/>
<ColumnDefinition Width="80"/>
</Grid.ColumnDefinitions>
<Label Grid.Row="0" Grid.Column="0" Text="{Binding NumType}" Margin="0,0,0,0" />
<Label Grid.Row="0" Grid.Column="1" Text="{Binding LocationCode}" Margin="0,0,0,0" />
<CheckBox Grid.Row="0" Grid.Column="2" IsChecked="{Binding IsChecked}">
<CheckBox.Behaviors>
<xct:EventToCommandBehavior
Command="{Binding BindingContext.UpdateThisItemCommand, Source={x:Reference listview}}"
CommandParameter="{Binding .}"
EventName="CheckedChanged" />
</CheckBox.Behaviors>
</CheckBox>
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>