Object reference not set to an instance of an object.一般是什么原因造成？

[alanzhou]

Object reference not set to an instance of an object.一般是什么原因造成？

[linfengcyl]

译:未将对象引用到对象的实例.
声明了变量,但是没有赋值,仍然为null.用的时候就会报错.

[速马]

比如：

string GetText()
{
return null;
}

void ParseText()
{
string[] values = GetText().Split(',');
}

[MyLf]

就是没有实例化一个对象啦

[xianggang101]

或者你用的变量根本就没有！

[alanzhou]

谢谢，找到那个未实例化的对象了。
看别人的代码挺累的。

[alanzhou]

ok,搞定了，谢谢3tzjq(永不言弃)。

为什么会这样？

[3tzjq]

string 类型应该用 if (marshalColumn != string.Empty) 判断。而marshalColumn = "" 和 marshalColumn = string.Empty 结果是一样的！所以不用判断。

[cdo]

就是该对象为null

[xamaizi]

变量为初始化造成的

[alanzhou]

居然还是报这个错！
还要检查。

搞定了就给分

[alanzhou]

这是用C#写COM给asp调。我在工程里用vbs来测。

public void InsertData(object a,object orderform)
{
string sql = string.Format("SELECT * FROM {0} WHERE {1} = @{1} ", tableNamne, primaryKey); //这个我试过输出了正确
#if DEBUG
Console.Write("marshalColumn=" + marshalColumn + "!"); //marshalColumn是private property,这里输出 marshalColumn=！
#endif
if(marshalColumn != "")
{
fac = new OrderFormFac(connectionString, sql,marshalColumn,"^_.*");
OrderForm objOrderF = orderform as OrderForm;
fac.Save(objOrderF);
}
else
{
#if DEBUG
Console.Write("marshalColumn=" + marshalColumn + "!"); //这里没有输出
#endif

fac = new OrderFormFac(connectionString,sql);
Dictionary objShopper = orderform as Dictionary;
#if DEBUG
Console.Write("orderform.shopper_id=" + objShopper["shopper_id"]);
#endif
fac.SaveAs(objShopper);
}

}

然后错误信息Object reference not set to an instance of an object

这么怎么回事？

[3tzjq]

可疑代码：
OrderForm objOrderF = orderform as OrderForm;

Dictionary objShopper = orderform as Dictionary;

fac.Save(objOrderF|objShopper); 时可能objShopper = null。
if(obj... != null)fac.Save(obj...)

[alanzhou]

else
{
#if DEBUG
Console.Write("marshalColumn=" + marshalColumn + "!"); //这里没有输出
#endif

这里就没有输出了，到不了下面的代码

[3tzjq]

贴出你的 marshalColumn 属性看一下。

[alanzhou]

private string marshalColumn;

public void InitStorage(string sConnectionString,string sTable,string sKey,string sProgID,string sMarshalColumn,string sDateChanged)
{
connectionString = sConnectionString;
tableNamne = sTable;
primaryKey = sKey;
if(!Convert.IsDBNull(sProgID))
progID = sProgID;
else
progID = string.Empty;

if(!Convert.IsDBNull(sMarshalColumn))
marshalColumn = sMarshalColumn;
else
marshalColumn = "";
if(!Convert.IsDBNull(sDateChanged))
dateChanged = sDateChanged;
else
dateChanged = string.Empty;
}
这个在InsertData之前调用了

[3tzjq]

if(!Convert.IsDBNull(sMarshalColumn))
marshalColumn = sMarshalColumn;
else
marshalColumn = "";

直接改为：marshalColumn = sMarshalColumn;

[易酷天]

private string marshalColumn;

public void InitStorage(string sConnectionString,string sTable,string sKey,string sProgID,string sMarshalColumn,string sDateChanged)
{
connectionString = sConnectionString;
tableNamne = sTable;
primaryKey = sKey;
if(!Convert.IsDBNull(sProgID))
progID = sProgID;
else
progID = string.Empty;

if(!Convert.IsDBNull(sMarshalColumn))
marshalColumn = sMarshalColumn;
else
marshalColumn = " ";
if(!Convert.IsDBNull(sDateChanged))
dateChanged = sDateChanged;
else
dateChanged = string.Empty;
}
这个在InsertData之前调用了