MVVMLight WPF ProgressBar 在異步任務中綁定

Question

誰能告訴我為什么我的ProgressBar在Task結束之前無法更新？

ProgressBar值綁定到我的 ViewModel 屬性，稱為ProgressCurrentValue ； 並且例程在Task中。 我還嘗試使用 MVVMLight 的DispatcherHelper.CheckBeginInvokeOnUI() function 更新 UI 線程上的ProgressCurrentValue ，但仍然沒有成功。 我確定我遺漏了一些明顯的東西； 任何人都可以看到嗎？

風景

<UserControl x:Class="xxxxxx.Views.ProcessingView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:xxxxxx.Views"
             mc:Ignorable="d" 
             DataContext="{Binding ProcessingVM, Source={StaticResource Locator}}"
             x:Name="RunningControl">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <ProgressBar Grid.Row="0" Maximum="{Binding ProgressMaximum}" Minimum="{Binding ProgressMinimum}" Value="{Binding ProgressCurrentValue}" Height="20" />
        <!-- etc. -->
    </Grid>
</UserControl>

ViewModel（相關部分）

    private int _progressMinimum;
    /// <summary>
    ///   Gets or sets the minimum of the progress control.
    /// </summary>
    public int ProgressMinimum
    {
        get { return _progressMinimum; }
        set { Set(ref _progressMinimum, value); }
    }

    private int _progressMaximum;
    /// <summary>
    ///   Gets or sets the maximum of the progress control.
    /// </summary>
    public int ProgressMaximum
    {
        get { return _progressMaximum; }
        set { Set(ref _progressMaximum, value); }
    }

    private int _progressCurrentValue;
    /// <summary>
    ///   Gets or sets the current value of the progress control.
    /// </summary>
    public int ProgressCurrentValue
    {
        get { return _progressCurrentValue; }
        set { Set(ref _progressCurrentValue, value); }
    }

    private async Task ProcessCSVFiles(string[] fullpaths)
    {
        // Get the current settings for use in the data processing.
        ObjectStringPair setting = await _service.FirstSettingAsync();
        if (!(setting.Item is Setting s))
        {
            await SendFlashMessageAsync(new FlashMessage("Unable to locate settings.", AlertLevels.Danger));
            return;
        }

        // Set the progress parameters.
        ProgressProcessText = "Processing " + ((fullpaths.Length == 1) ? Path.GetFileName(fullpaths[0]) : "multiple files") + " ...";
        ProgressMinimum = 0;
        ProgressMaximum = 100;
        ProgressCurrentValue = 0;

        // Convert the CSV files to DataTables.
        List<DataTable> tables = new List<DataTable>();
        int i = 0;
        int rowCount = 0;
        foreach(string fullname in fullpaths)
        {
            ObjectStringPair reader = await _service.GetDataTableWithCSVHeadersAsync(fullname, headers);
            if (reader.Item is DataTable dt)
            {
                tables.Add(dt);
                rowCount += dt.Rows.Count;
            }
            i++;
        }

        // Abandon if there are no datatables.
        if (tables.Count == 0) { return; }

        double progressIncrement = rowCount / 100;

        rowCount = 0;
        foreach (DataTable table in tables)
        {
            foreach (DataRow row in table.Rows)
            {
                // Update the progress control.
                rowCount++;
                if ((int)(rowCount / progressIncrement) > ProgressCurrentValue)
                {
                    ProgressCurrentValue = (int)(rowCount / progressIncrement);
                }

                // Processing code.
            }
        }

        // Close the progress control.
    }

Answer 1

啊，我真是個笨蛋。

問題是Task是從 MVVMLight IMessenger 的回調中調用的，而 MVVMLight IMessenger本身是從 Button RelayCommand發送的。 結果，似乎一切都保留在 UIThread 上。

也許這對大多數人來說是顯而易見的，但我沒有發現它。 答案是明確地在后台線程上調用Task 。 所以而不是：

await ProcessCSVFiles(...);

我不得不打電話：

await Task.Run(() => ProcessCSVFiles(...);

不確定我的診斷是否正確，所以我很樂意任何人糾正我，但上面的解決方案似乎有效。