如何在wpf mvvm中使用组合框 [英] How can I use combobox with wpf mvvm

问题描述

我有一个员工表。员工表中的位置和位置字段。
我必须使用combobox进行过滤。如果我在组合框中选择 A地点，则只有A地点人员应该进入屏幕；如果我选择B地点，则只有B地点人员应该进入屏幕。
这是我的xaml条目和ComboBox。ParticularEntries是我的所有条目（A和B位置在一起）

I have an employee table. and location field in employee table. I have to use combobox to filter that. If I choose "A location" in combobox only A location people should come in screen if I choose B location only B location people should come in screen. It's my xaml Entries and ComboBox.ParticularEntries is my all entries (A and B locations together)

Initialized ParticularEntries就是这样：

Initialized ParticularEntries like that:

private IEnumerable<EntryReportParticular> _particularEntries;
public IEnumerable<EntryReportParticular> ParticularEntries
{
    get { return _particularEntries; }
    set { Set(ref _particularEntries, value); }
}

和EntryReportSpecial Model类：

And EntryReportParticular Model Class:

public class EntryReportParticular : BindableItem
{
    private Employee _employee;
    public Employee Employee
    {
        get { return _employee; }
        set { Set(ref _employee, value); }
    }

    private DateTime _entry;
    public DateTime Entry
    {
        get { return _entry; }
        set { Set(ref _entry, value, () => OnPropertyChanged(nameof(Duration))); }
    }

    private DateTime _exit;
    public DateTime Exit
    {
        get { return _exit; }
        set { Set(ref _exit, value, () => OnPropertyChanged(nameof(Duration))); }
    }

    public TimeSpan Duration { get { return Exit - Entry; } }

    private Region _region;
    public Region Region
    {
        get { return _region; }
        set { Set(ref _region, value); }
    }
}

这是我的xaml ParticularEntries

It's my xaml ParticularEntries

<DataGrid  
    ItemsSource="{Binding ParticularEntries}" 
    AutoGenerateColumns="False" 
    IsReadOnly="True" 
    RowHeaderWidth="0" 
    GridLinesVisibility="All"
    HorizontalGridLinesBrush="WhiteSmoke"
    VerticalGridLinesBrush="WhiteSmoke" 
    Margin="4">

这是我的命令组合框。

<ComboBox 
    ItemsSource="{Binding Locations}" 
    SelectedItem ="{Binding SelectedLocation}">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="SelectionChanged">
            <i:InvokeCommandAction Command="{Binding LocationFilterCommand}"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>
</ComboBox>

这是我与ViewModel相关的部分：
ComboBox：

And It's my related part of ViewModel: ComboBox:

private string _selectedLocation;
public string SelectedLocation
{
    get { return _selectedLocation; }
    set
    {
        _selectedLocation = value;
        OnPropertyChanged("SelectedLocation");
        Trace.WriteLine(SelectedLocation);
    }
}

private ObservableCollection<string> _locations;
public ObservableCollection<string> Locations
{
    get { return _locations; }
    set
    {
        _locations = value;
        OnPropertyChanged("Locations");
    }
}

public EntryReportViewModel()//Constructor
{
    Locations = new ObservableCollection<string>()
    {
        "A Location","B Location"
    };
}

LocationFilterCommand（根据位置进行过滤，不带按钮）

LocationFilterCommand(to filtered according to location without button)

#region LocationFilterCommand

private DelegateCommand _locationFilterCommand;
public DelegateCommand LocationFilterCommand
{
    get { return _locationFilterCommand ?? (_locationFilterCommand = new DelegateCommand(CanLocationFilter, LocationFilter)); }
}

private bool CanLocationFilter()
{

    if (ParticularEntries == null || DailyEntries == null || MonthlyEntries == null)
        return false;

    return true;
}
private void LocationFilter()
{
   ParticularEntries.Select(pg => pg.Region.Location == _selectedLocation);
   MonthlyEntries.Select(pg => pg.Employee.CostCenter.Location == _selectedLocation);

}
#endregion

我是这样做的。我的ComboBox具有A和B位置，但是当我选择A或B位置时，任何更改。如何解决此问题以及如何根据位置进行过滤？我应该在UI或其他应用程序中进行哪些更改？

I did that. I have ComboBox with A and B locations but when I choose A or B location anything changed.How can I fix this and how can I filtered according to location? What should I change in UI or others to do that?

推荐答案

您在 LocationFilter中的代码毫无意义。

ParticularEntries.Select(pg => pg.Region.Location == _selectedLocation);

它将返回 IEnumerable< bool> ，但是

如果要过滤，则必须使用 Where 。

If you want to filter, you have to use Where.

但是即使您将代码更改为

But even if you change your code to

ParticularEntries = ParticularEntries.Where(pg => pg.Region.Location == _selectedLocation);

您将看到一个变化，但是下次选择其他位置时，您将面临下一个问题。

you will see a change, but you will face the next problem next time when you select a different location.

您需要一个集合，其中所有未过滤的项存储在私有字段中，并将其用于过滤

You need a collection with all unfiltered items stored inside a private field and use that for filtering.

private IEnumerable<EntryReportParticular> _allEntries;

private IEnumerable<EntryReportParticular> _particularEntries;
public IEnumerable<EntryReportParticular> ParticularEntries
{
    get { return _particularEntries; }
    set { Set(ref _particularEntries, value); }
}

private void LocationFilter()
{
   ParticularEntries = _allEntries
       .Where(pg => pg.Region.Location == _selectedLocation)
       .ToList();
}

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