未將對象引用設置爲arrayList對象的實例

Question

有問題。在Program.cs中我有

public static ArrayList VKgroup_VKtoOD { get; set; }

在窗體2我試圖挽救combobox1到VKgroup_VKtoOD所有項目，但收到的異常

Object reference not set to an instance of an object 

代碼：

 foreach (object item in comboBox1.Items) 
     { 
       Data.VKgroup_VKtoOD.Add(item); 

     } 

爲什麼？這一個

public static ArrayList VKgroup_VKtoOD { get; set; } 

：

Answer 1

確保使用

Data.VKgroup_VKtoOD = new ArrayList(); 
foreach (object item in comboBox1.Items) 
     { 
       Data.VKgroup_VKtoOD.Add(item); 

     } 

Answer 2

你應該初始化數組前初始化ArrayList中，將這段代碼

public static ArrayList VKgroup_VKtoOD { 

get{ 
if (VKgroup_VKtoOD ==null) 
    VKgroup_VKtoOD =new ArrayList(); 
return VKgroup_VKtoOD ; 
} 

set{ 
    VKgroup_VKtoOD =value; 
} 
}