向图表添加点时的Nullreferenceexception

时间:2014-01-29 20:01:28

标签: c# winforms graph nullreferenceexception

创建图表:

    private Chart mainChart;
    private void createChart()
    {
        mainChart = new Chart
        {
            Dock = DockStyle.Fill,
            Name = "chart1",
        };
        mainChart.ChartAreas.Add(new ChartArea());
        mainChart.Legends.Add(new Legend());

        mainChart.ChartAreas[0].AxisX.Minimum = 1;
        for (int i = 0; i < 32; i++)
        {
            mainChart.Series.Add(new Series
            {
                Name = "test" + i,
                LegendText = "Test " + (i + 1).ToString().PadLeft(2, '0'),
                ChartType = SeriesChartType.FastLine,
            });
        }
    }

图表属性:

public Chart chart
{
    get
    {
        return mainChart;
    }
    set
    {
        mainChart = value;
        Form activeChild = FormAlreadyLoaded("Child_Chart");
        if (activeChild != null)
        {
            Chart frmchart = activeChild.Controls.Find("chart1", true).FirstOrDefault() as Chart;
            frmchart = mainChart;
        }
    }
}

FormAlreadyLoaded方法:

private Form FormAlreadyLoaded(string formName)
{
    foreach (Form frm in this.MdiChildren)
        if (frm.Name.Equals(formName))
            return frm;
    return null;
}

Child_Chart是一个简单的表单,在“加载”方法中使用它:

MainForm parent = this.MdiParent as MainForm;
this.Controls.Add(parent.chart);

添加到图表(发生错误的地方)

chart.Series[i].Points.AddXY(value1,value2);

例外文字:

    System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Forms.DataVisualization.Charting.Chart.get_Series()
   at Oasis.MainForm.<>c__DisplayClass13.<ProcessSerial>b__11() in MainForm.cs:line 355
   at System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(Object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Forms.Control.InvokeMarshaledCallback(ThreadMethodEntry tme)
   at System.Windows.Forms.Control.InvokeMarshaledCallbacks()

更多信息:

createChart()是主窗体的load事件中调用的第一个东西。

导致错误的代码行位于

this.BeginInvoke(new MethodInvoker(delegate()

在serialPort的DataRecieved事件中

出现错误后'mainChart'的本地值i.imgur.com/LZSY3Iw.png

所有这些代码都可以正常工作,直到我关闭“Child_Chart”。

2 个答案:

答案 0 :(得分:0)

由于series [i]的Points属性可能是非基本类型,您需要使用'new'关键字

使用其构造函数初始化它

答案 1 :(得分:0)

你确定chart不是什么?我没有看到调用CreateChart()的位置,我没有看到私有字段mainChart被实例化的其他任何地方。

除此之外,您需要打破错误并查看哪个是空引用。它可以是chartchart.Serieschart.Series[i],依此类推整个声明。