如何解决对象引用未设置为我的代码中的对象实例 [英] How Can I Solve Object Reference Not Set To An Instance Of An Object In My Code

问题描述

private void CreateBarGraph()
{
   string strCaption = "Attendence Performance Percentage wise";
   string strSubCaption = "For DPS2013-2014";
   string xAxis = "Name";
   string yAxis = "Percentage";

   //strXML will be used to store the entire XML document generated
   string strXML = null;

   //Generate the graph element
   strXML = @"
pieSliceDepth='30' formatNumberScale='0'
xAxisName='" + xAxis + @"' yAxisName='" + yAxis + @"' rotateNames='1'
>";
    
    int i = 0;
    dt = (DataTable)Session["row"];
    foreach (DataRow dr2 in dt.Rows)
    {
       strXML += " i++";
    }

    //Finally, close element
    strXML += "";

    FCLiteral2.Text = FusionCharts.RenderChartHTML("FusionCharts/FCF_Column3D.swf", // Path to chart's SWF
                                                            "", // Leave blank when using Data String method
                                                            strXML, // xmlStr contains the chart data
                                                            "mygraph1", // Unique chart ID
                                                            GraphWidth, GraphHeight, // Width & Height of chart
                                                            false
                                                            );
}

推荐答案

您可以通过阅读这个 [ ^ ]或 this [ ^ ]。



此错误消息是告诉你需要提供一个存在的变量对象或至少有一个值。

You can solve this problem by reading this[^] or this[^].

This error message is telling you that you need to provide a variable object that exists or atleast has a value.

我们无法确切地说出来，部分是因为你没有告诉我们哪一行给你问题，部分是因为我们无法运行你的代码。但......最可能的原因不在于该代码。



我怀疑问题出现在这里：

We can't tell exactly, partly because you don;t tell us which line gives you the problem, and partly because we can't run your code. But...the most likely reason is not in that code.

I suspect that the problem occurs here:

foreach (DataRow dr2 in dt.Rows)

并由此引起：

And is "caused" by this:

dt = (DataTable)Session["row"];

如果你的Session没有包含row的值，则返回null，当你尝试使用 dt.Rows 时，它将会结果抛出一个空引用异常。



至于为什么你的Session什么都没有，我可以说 - 你需要先看看你放的是什么进入会议并仔细检查该部分。

我们不能为你做到这一点！

If your Session contains no value for "row" is will return null, and when your try to use dt.Rows it will throw a null reference exception as a result.

By as to why your Session contains nothing, I can;t say - you need to start by looking at what you put into the Session and check that part very carefully.
We can't do that for you!

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