Question

我的应用程序中有多个viewModel，并在ViewModelLocator mvvm light中绑定/使用它们。我在DailyActivities.xaml页面上做了一个按钮。但是当我点击它时，它在ViewModelLocator中给出了错误，例如“对象引用未设置为对象的实例”。和控制来到这一行：

public static void ClearActivities（） { _activities.Cleanup（）; //这里错误 _activities = null; }

这是ViewModelLocator中DailyActivitiesViewModel的代码：

private static ActivitiesViewModel _activities;

          public static ActivitiesViewModel ActivitiesStatic
    {
        get
        {
            if (_activities == null)
            {
                CreateActivities();
            }

            return _activities;
        }
    }

    /// <summary>
    /// Gets the ViewModelPropertyName property.
    /// </summary>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance",
        "CA1822:MarkMembersAsStatic",
        Justification = "This non-static member is needed for data binding purposes.")]
    public ActivitiesViewModel Activities
    {
        get
        {
            return ActivitiesStatic;
        }
    }

    /// <summary>
    /// Provides a deterministic way to delete the ViewModelPropertyName property.
    /// </summary>
    public static void ClearActivities()
    {
        _activities.Cleanup(); --Error here
        _activities = null;
    }

    /// <summary>
    /// Provides a deterministic way to create the ViewModelPropertyName property.
    /// </summary>
    public static void CreateActivities()
    {
        if (_activities == null)
        {
            _activities = new ActivitiesViewModel();
        }
    }

请建议？

由于

Answer 1

在使用之前，您需要确定该字段是否存在：似乎字段_activities已经为null，因此不需要清理。

为什么不做像

这样的事情

public static void ClearActivites()
{
    if (null == _activities) return;
    _activities.Cleanup();
    _activities = null;
}

对象引用未设置为ViewModelLocator Mvvm Light中对象的实例

1 个答案: