How to make a checkbox stay checked when i navigate through pages? Xamarin - xamarin.forms

Question

I have this listview and in the listview I have an ItemTemplate with a DataTemplate and a ViewCell in which I have a checkbox named "box1". I want to make it stay checked when i switch pages, but i can't acess it via name because it is in a DataTemplate and in a ViewCell. I have tried to name all the controls down to the checkbox and get access to it like that, but it does not seem to work...
This is my xaml:
<ListView SeparatorVisibility="None"
BackgroundColor="Transparent"
VerticalOptions="Center"
x:Name="listView"
HasUnevenRows="True"
>
<ListView.ItemTemplate>
<DataTemplate x:DataType="model:Meal"
x:Name="mydt"
>
<ViewCell
x:Name="myvc"
>
<Grid BackgroundColor="Transparent"
x:Name="mygrid"
>
<Frame BackgroundColor="Transparent"
CornerRadius="20"
x:Name="myframe"
>
<StackLayout Orientation="Horizontal"
>
<Image Source="meal.png" WidthRequest="59" Margin="0, 0, 15, 0"/>
<StackLayout Orientation="Vertical" WidthRequest="300">
<Label VerticalOptions="Start"
FontSize="20"
Text="{Binding Name}"
FontAttributes="Bold"/>
<Label VerticalOptions="Start"
FontSize="15"
Text="{Binding Ingredients}"/>
<StackLayout Orientation="Horizontal">
<Label VerticalOptions="Start"
FontSize="15"
Text="{Binding Calories}"
TextColor="OrangeRed"/>
<Label Text="kcal"
FontSize="15"
TextColor="OrangeRed"/>
</StackLayout>
</StackLayout>
<CheckBox
x:Name="box1"
IsChecked="{Binding Checked}"
Color="Green"
Margin="60, 0, 0, 0"
CheckedChanged="box1_CheckedChanged"
BindingContext="{Binding ., Mode=TwoWay}"
/>
</StackLayout>
</Frame>
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
This is my event handler from the Content Page in cs:
private void box1_CheckedChanged(object sender, CheckedChangedEventArgs e)
{
var meal = listView.SelectedItem as Meal;
if (listView.SelectedItem != null)
{
if (e.Value == true)
{
long cal = long.Parse(meal.Calories);
calories_consumed = calories_consumed + cal;
ch = true;
}
else
{
long cal = long.Parse(meal.Calories);
calories_consumed = calories_consumed - cal;
ch = false;
}
}
label_cal.Text = calories_consumed.ToString();
}
This is my updated Meal class using INotifyPropertyChanged:
public class Meal : INotifyPropertyChanged
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
private string name;
public string Name
{
get { return name; }
set
{
name = value;
OnPropertyChanged(nameof(Name));
}
}
private string ingredients;
public string Ingredients
{
get { return ingredients; }
set
{
ingredients = value;
OnPropertyChanged(nameof(Ingredients));
}
}
private string calories;
public string Calories
{
get { return calories; }
set
{
calories = value;
OnPropertyChanged(nameof(Calories));
}
}
private bool isChecked;
public bool IsChecked
{
get
{
return isChecked;
}
set
{
isChecked = value;
OnPropertyChanged(nameof(IsChecked));
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
And this is my code behind for the ContentPage:
protected override async void OnAppearing()
{
base.OnAppearing();
listView.ItemsSource = new ObservableCollection<Meal>(await App.Database.GetMealAsync());
}
public static bool ch;
Event handler for the checkbox in the code behind:
private void box1_CheckedChanged(object sender, CheckedChangedEventArgs e)
{
var meal = listView.SelectedItem as Meal;
if (listView.SelectedItem != null)
{
if (e.Value == true)
{
long cal = long.Parse(meal.Calories);
calories_consumed = calories_consumed + cal;
ch = true;
}
else
{
long cal = long.Parse(meal.Calories);
calories_consumed = calories_consumed - cal;
ch = false;
}
}
meal.IsChecked = ch;
label_cal.Text = calories_consumed.ToString();
}

Answer 1

To be short you can just save the value in Preferences or make a variable in a model that is static and bind that values OnAppearing

Answer 2

There are mainly two ways that you could store the checkbox's state.
1.You could use Json to Serialize and deserialize the model that has a IsChecked property that binding with the checkbox.For more details, you could refer to this thread.
Code in checkbox_CheckedChanged event:
private void checkbox_CheckedChanged(object sender, CheckedChangedEventArgs e)
{
var checkbox = (CheckBox)sender;
var selectMeal = checkbox.BindingContext as Meal;
selectMeal.Checked = e.Value;
//save the data and checkbox state,you could save the data as a json string
string json = JsonConvert.SerializeObject(blistView);
Preferences.Set("listmeals", json);
}
2.You could store the state of the checkbox using sqlite-net-pcl.Please refer to below MS official docs for more details.
And then retrieve the check state of the checkbox via OnAppearing Method.
protected override void OnAppearing()
{
// retrieve the check state of the checkbox in your sqlite database.
base.OnAppearing();
TodoItemDatabase database = await TodoItemDatabase.Instance;
listView.ItemsSource = await database.GetItemsAsync();
}
MS official docs:https://learn.microsoft.com/en-us/xamarin/xamarin-forms/data-cloud/data/databases

Answer 3

The way you are connecting your class your view/xaml is incorrect. If you want to do it without MVVM you can go about it by creating a model that implements INotifyPropertyChanged and an ObservableCollection as listView itemssource.
Model class Meal could look like this:
public class Meal : INotifyPropertyChanged
{
private string name;
public string Name
{
get { return name; }
set
{
name = value;
OnPropertyChanged(nameof(Name));
}
}
private string ingredients;
public string Ingredients
{
get { return ingredients; }
set
{
ingredients = value;
OnPropertyChanged(nameof(Ingredients));
}
}
private string calories;
public string Calories
{
get { return calories; }
set
{
calories = value;
OnPropertyChanged(nameof(Calories));
}
}
private bool isChecked;
public bool IsChecked
{
get { return isChecked; }
set
{
isChecked = value;
OnPropertyChanged(nameof(IsChecked));
}
}
#region INotify property changed
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
}
The MainPage.xaml like this:
<StackLayout>
<ListView SeparatorVisibility="None"
BackgroundColor="Transparent"
VerticalOptions="Center"
x:Name="listView"
HasUnevenRows="True">
<ListView.ItemTemplate>
<DataTemplate x:DataType="model:Meal" x:Name="mydt" >
<ViewCell x:Name="myvc" >
<Grid BackgroundColor="Transparent"
x:Name="mygrid" >
<Frame BackgroundColor="Transparent"
CornerRadius="20"
x:Name="myframe">
<StackLayout Orientation="Horizontal">
<Image Source="meal.png" WidthRequest="59" Margin="0, 0, 15, 0"/>
<StackLayout Orientation="Vertical" WidthRequest="300">
<Label VerticalOptions="Start"
FontSize="20"
Text="{Binding Name}"
FontAttributes="Bold"/>
<Label VerticalOptions="Start"
FontSize="15"
Text="{Binding Ingredients}"/>
<StackLayout Orientation="Horizontal">
<Label VerticalOptions="Start"
FontSize="15"
Text="{Binding Calories}"
TextColor="OrangeRed"/>
<Label Text="kcal" FontSize="15" TextColor="OrangeRed"/>
</StackLayout>
</StackLayout>
<CheckBox x:Name="box1" IsChecked="{Binding IsChecked}" Color="Green" Margin="60, 0, 0, 0" />
</StackLayout>
</Frame>
</Grid>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
<Button Clicked="Button_Clicked" Text="Check status items"/>
</StackLayout>
And your MainPage.xaml.cs code behind like this:
public partial class MainPage : ContentPage
{
public MainPage()
{
InitializeComponent();
}
protected override void OnAppearing()
{
base.OnAppearing();
listView.ItemsSource = new ObservableCollection<Meal>(new List<Meal>
{
new Meal { Name = "Meal 01", Ingredients = "Ingredients 01", Calories = "250" },
new Meal { Name = "Meal 02", Ingredients = "Ingredients 02", Calories = "350" },
new Meal { Name = "Meal 03", Ingredients = "Ingredients 03", Calories = "450" }
});
}
/// <summary>
/// check items ischecked status
/// </summary>
private void Button_Clicked(object sender, EventArgs e)
{
foreach (var item in listView.ItemsSource)
{
if (item is Meal meal && meal.IsChecked)
System.Diagnostics.Debug.WriteLine($"{meal.Name} is checked");
}
}
}
Look at the other answer for saving the model and/or list. When saved the list can be retrieved in the OnAppearing and set instead of recreated as shown in this example. I've added a button on the bottom that prints out which Meals are selected in the output window. See screenshot: