c# – 为什么SynchronizationContext.Current为null？

下面的算法有效.
我尝试了,然后我将Winform项目删除到另一个目录,并且SynchronizationContext.Current为null.
为什么？

SynchronizationContext uiCtx = SynchronizationContext.Current;  

private void backgroundWorker1_DoWork(object sender,DoWorkEventArgs e)
{
    int[] makeSelfMoves = new int[4];

    lock (replay)
    {
        // count should be more than 2
        foreach (KeyValuePair<int,int[]> item in replay)
        {              
            makeSelfMoves = replay[item.Key];
            codeFile.ExecuteAll(makeSelfMoves[0],makeSelfMoves[1],makeSelfMoves[2],makeSelfMoves[3]);

            // i get the error here. uictx is null
            uiCtx.Post(o =>
            {
                PrintPieces(codeFile.PieceState());
            },null);                               

            System.Threading.Thread.Sleep(1000);
        }
    }
}