在AutomationPeer类中实现IGridProvider，IValueProvider

Question

我为自定义控件编写了AutomationPeer类：

    // Automation Peer for the CustomControl
    private class CustommControlAutomationPeer : FrameworkElementAutomationPeer, IValueProvider, IGridProvider
    {
        public CustomControlAutomationPeer(CustomControl control)
            : base(control)
        { }

        #region overriding the "Core" methods from the base automation peer class that describe behavior unique and specific to custom control
         ...
        #endregion

        #region overriding of GetPattern should return the object that implements the specified pattern
        public override object GetPattern(PatternInterface patternInterface)
        {
            if (patternInterface == PatternInterface.Grid || patternInterface == PatternInterface.Value)
            {
                return this;
            }
            return base.GetPattern(patternInterface);
        }

        #endregion

        #region IGridProvider
         ...
        #endregion

        #region IValueProvider
         ...
        #endregion

        /// <summary>
        /// Pointer to CustomControl
        /// </summary>
        private CustomControl Control
        {
            get
            {
                return (CustonControl)base.Owner;
            }
        }
    }

在计算机中，安装了Visual Studio和其他计算机，在那里安装了测试代理，我用代码启动了testmethod：

AutomationPattern[] supportedPatterns = customControl.GetSupportedPatterns();
        foreach (var supPattern in supportedPatterns)
            Trace.WriteLine(supPattern.ProgrammaticName);

跟踪结果：

在带有visual studio的计算机中：

QTAgent32.exe, <a class=success>Playback - {43} [SUCCESS] MouseButtonClick - "[UIA]ControlType='RadioButton' && AutomationId='allCriteriaRadioButton'"
\0</a>  
**ValuePatternIdentifiers.Pattern;  
GridPatternIdentifiers.Pattern**  
QTAgent32.exe, IEDOM : StopSession of the plugin called before StartSession
QTAgent32.exe, UIA : StopSession of the plugin called before StartSession

在带有测试代理的计算机中：

QTAgent32.exe, <a class=success>Playback - {43} [SUCCESS] MouseButtonClick - "[UIA]ControlType='RadioButton' && AutomationId='allCriteriaRadioButton'"
\0</a>  
**GridPatternIdentifiers.Pattern**  
 QTAgent32.exe, IEDOM : StopSession of the plugin called before StartSession
QTAgent32.exe, UIA : StopSession of the plugin called before StartSession

为什么我在第二种情况下只得到IGridProvider？