NAudio和ZedGraph波形图

    int window;
    LineItem myCurve1;
    LineItem myCurve2;
    public void DrawWave(ZedGraphControl zgc)
    {
        NAudio.Wave.WaveChannel32 wave = new NAudio.Wave.WaveChannel32(new NAudio.Wave.WaveFileReader(open.FileName));
        WaveFileReader wavFile = new WaveFileReader(open.FileName);
        byte[] mainBuffer = new byte[wave.Length];
        float fileSize = (float)wavFile.Length / 1048576;
        if (fileSize < 2)
            window = 8;
        else if (fileSize > 2 && fileSize < 4)
            window = 16;
        else if (fileSize > 4 && fileSize < 8)
            window = 32;
        else if (fileSize > 8 && fileSize < 12)
            window = 128;
        else if (fileSize > 12 && fileSize < 20)
            window = 256;
        else if (fileSize > 20 && fileSize < 30)
            window = 512;
        else
            window = 2048;
        float[] fbuffer = new float[mainBuffer.Length / window];
        wave.Read(mainBuffer, 0, mainBuffer.Length);
        for (int i = 0; i < fbuffer.Length; i++)
        {
            fbuffer[i] = (BitConverter.ToSingle(mainBuffer, i * window));
        }
        double time = wave.TotalTime.TotalSeconds;
        GraphPane myPane = zgc.GraphPane;
        PointPairList list1 = new PointPairList();
        PointPairList list2 = new PointPairList();
        for (int i = 0; i < fbuffer.Length; i++)
        {
            list1.Add(i, fbuffer[i]);
        }
        list2.Add(0, 0);
        list2.Add(time, 0);
        if (myCurve1 != null && myCurve2 != null)
        {
            myCurve1.Clear();
            myCurve2.Clear();
        }
        myCurve1 = myPane.AddCurve(null, list1, Color.Red, SymbolType.None);
        myCurve1.IsX2Axis = true;
        myCurve2 = myPane.AddCurve(null, list2, Color.Black, SymbolType.None);
        myPane.XAxis.Scale.MaxAuto = true;
        myPane.XAxis.Scale.MinAuto = true;
        zgc.AxisChange();
        zgc.Invalidate();
    }

我有这段代码在 ZedGraph 中绘制波形。除了一件事外，它工作正常。绘制波形后，我选择要绘制的新文件，但必须清除旧文件。我试图在全局中定义LineItem，以便我可以编写if(myCruver != null) myCurve.Clear();这种情况。但是，它不会清除旧图形。我应该怎么做才能解决这个问题？

    int window;
    LineItem myCurve1;
    LineItem myCurve2;
    public void DrawWave(ZedGraphControl zgc)
    {
        NAudio.Wave.WaveChannel32 wave = new NAudio.Wave.WaveChannel32(new NAudio.Wave.WaveFileReader(open.FileName));
        WaveFileReader wavFile = new WaveFileReader(open.FileName);
        byte[] mainBuffer = new byte[wave.Length];
        float fileSize = (float)wavFile.Length / 1048576;
        if (fileSize < 2)
            window = 8;
        else if (fileSize > 2 && fileSize < 4)
            window = 16;
        else if (fileSize > 4 && fileSize < 8)
            window = 32;
        else if (fileSize > 8 && fileSize < 12)
            window = 128;
        else if (fileSize > 12 && fileSize < 20)
            window = 256;
        else if (fileSize > 20 && fileSize < 30)
            window = 512;
        else
            window = 2048;
        float[] fbuffer = new float[mainBuffer.Length / window];
        wave.Read(mainBuffer, 0, mainBuffer.Length);
        for (int i = 0; i < fbuffer.Length; i++)
        {
            fbuffer[i] = (BitConverter.ToSingle(mainBuffer, i * window));
        }
        double time = wave.TotalTime.TotalSeconds;
        GraphPane myPane = zgc.GraphPane;
        PointPairList list1 = new PointPairList();
        PointPairList list2 = new PointPairList();
        for (int i = 0; i < fbuffer.Length; i++)
        {
            list1.Add(i, fbuffer[i]);
        }
        list2.Add(0, 0);
        list2.Add(time, 0);
        if (myCurve1 != null && myCurve2 != null)
        {
            myCurve1.Clear();
            myCurve2.Clear();
        }
        myCurve1 = myPane.AddCurve(null, list1, Color.Red, SymbolType.None);
        myCurve1.IsX2Axis = true;
        myCurve2 = myPane.AddCurve(null, list2, Color.Black, SymbolType.None);
        myPane.XAxis.Scale.MaxAuto = true;
        myPane.XAxis.Scale.MinAuto = true;
        zgc.AxisChange();
        zgc.Invalidate();
    }