我需要将表数据放入ListView（MVVM）

Question

Database connection and binding context are okay. Data can insert into a table without a problem. I need to add last of my table data row to a list view

<ListView ItemsSource="{Binding YourList}" 
          verticalOptions="FillAndExpand" >
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <StackLayout Orientation="Horizontal">
                    <Label Text="{Binding Catagoryview}"/>
                    <Label Text="{Binding Date}"/>
                    <Label Text="{Binding Expense}"/>

                </StackLayout>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

this is my XAML file. I create every property for in binding here. with backing fields.

in my ViewModel

private void add()
{
    database = new Database();
    var expensedata = database.GetExpenses(id);

    if (expensedata != null)
    {
        Catagoryview = expensedata.Catagory;
        Date= expensedata.Date;
        Expense = expensedata.Expense; 
    }
}

I know this code is not perfect. I really need to get the last 10 rows of my data into a list view.

also, here my get expenses method I used

public AddExpenses GetExpenses(int expense)
{
    return Conn.Table<AddExpenses>().FirstOrDefault(t => t.Id == expense);
}

Answer 1

To me it seems as if your add method does not actually add anything. In your viewmodel you'll need to have a public property YourList , which is propagated with add . Furthermore you are getting only one item from your expenses database, which won't work for adding 10 items.

The core question as far as I understood is

How can I add the 10 last items from an SQLite database to a Xamarin.Forms ListView using an MVVM approach.

Disregarding the fact that I do not know how and when you are calling add , I'll try to give an answer on how to get and add these elements.

First of all we need a property that will hold your items in your viewmodel. Depending on your requirements, either an IEnumerable<AddExpenses> or an ObservableCollection<AddExpenses> will do. I will demonstrate the ObservableCollection approach

ObservableCollection<AddExpenses> _expenses;

public ObservableCollection<AddExpenses> Expenses
{
    get
    {
        if(_expenses == null)
        {
            _expenses = new ObserrvableCollection<AddExpenses>();
        }
        return _expenses;
    }
}

You can bind to that property from your XAML

<ListView ItemsSource="{Binding Expenses}" 
      VerticalOptions="FillAndExpand">
<!-- What ever -->
</ListView>

And then add items to that collection from your AddExpenses method (I felt free to give it a more meaningful name):

private void AddExpenses()
{
    var database = new Database();
    var expenses = database.GetLastExpenses(numberOfExpenses: 10);

    foreach(var expense in expenses)
    {
        Expenses.Add(expense);
    }
}

Since we are now having objects of type AddExpenses in your collection, we'll have to change the binding in the ListView from Categoryview to Category :

<ListView ItemsSource="{Binding YourList}" 
          VerticalOptions="FillAndExpand">
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <StackLayout Orientation="Horizontal">
                    <Label Text="{Binding Category}"/>
                    <Label Text="{Binding Date}"/>
                    <Label Text="{Binding Expense}"/>
                </StackLayout>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

Last but not least we'll have to implement GetLastExpenses (this should work, while it's possible that there are better options)

public AddExpenses[] GetLastExpenses(int numberOfExpenses)
{
    return Conn.Table<AddExpenses>()
               .OrderByDescending(expenses => expenses.Date) 
               .Take(numberOfExpenses)
               .OrderBy(expenses => expenses.Date) // If you need them ordered ascending
               .ToArray()

}