C＃：对象到字符串数组。 [*]为[]错误（懂两种VB.NET和C＃帮助） [英] C#: Object to string array. [*] to [] error (Knowing both VB.NET as well as C# helps)

问题描述

我被分配到一个转换VB.NET工程到C＃和我被困。我使用了一个名为RsiOPCAuto类，但我不认为我会进入到太多细节到解释它是如何工作的。让我们只得到与我的问题。

那么basicly我做什么用这个code从我的类被抓的对象：

 公共部分类FrmPartialMain：表单
{
    RsiOPCAuto.OPCServer oOpcServer;
    公共FrmPartialMain（）
    {
        的InitializeComponent（）;
        反对RsiOPCAuto;
        反对oOPCList;        oOpcServer =新RsiOPCAuto.OPCServer（）;
        oOPCList = oOpcServer.GetOPCServers（）;
 

到目前为止，一切都很好。通过添加一块手表，我可以看到oOPCList现在有值{字符串[1..4]}。

现在我想把这四根弦成一个组合框。我做一个简单的for循环：

 的for（int i = 0; I＆LT; = oOPCList.Length;我++）
{
    cboServer.Items.Add（oOPCList [I]）;
}
 

的 修改：从头开始，改变了这一个好得多的foreach循环的

虽然这个对象，现在作为一个字符串数组都oOPCList.Length和（oOPCList [I]）得到错误：

。长度：
错误1'对象'不包含'长度'，没有扩展方法长度接受型对象的第一个参数的定义可以找到（是否缺少using指令或程序集引用？）

oOPCList [我]：
错误2无法应用与[]索引到类型的前pression对象

我敢打赌，这是最简单的事情，但我就是不能看到它，帮助是非常AP preciated，以及是否有其他任何你需要知道的一定要问： - ）

PS。这可能是值得一提，我已经尝试了一些不同的方法将对象转换为字符串数组，但我不断地得到一个错误，告诉我​​，我不能转换system.string [*]到system.string []。

这是VB.NET code，我转换：

 友元类frmPartialMain
    继承System.Windows.Forms.Form中
        昏暗oOpcServer作为RsiOPCAuto.OPCServer
        私人小组frmPartialMain_Load（BYVAL eventSender作为System.Object的，EventArgs的BYVAL作为System.EventArgs）把手MyBase.Load
            昏暗RsiOPCAuto作为对象
            昏暗oOPCList（）作为对象
            昏暗我作为整数            oOpcServer =新RsiOPCAuto.OPCServer
            oOPCList = oOpcServer.GetOPCServers
            对于i = LBOUND（oOPCList）为UBound函数（oOPCList）
                cboServer.Items.Add（oOPCList（I））
            接下来，我
 

解决方案

您需要 GetOPCServers 的返回值强制转换为对象第一，然后再切换到阵列，因为这个方法返回一个动态键入。你不能直接转换为的String [] ，因为强类型的数组，其不为0，基于不被C＃支持。中投后，您需要调用演员LT;串＆GT; 来得到一个强类型枚举的，在这你可以迭代：

 的IEnumerable＆LT;串GT; oOPCList;oOpcServer =新RsiOPCAuto.OPCServer（）;
oOPCList =（（阵列）（对象）oOpcServer.GetOPCServers（））演员LT;串＆GT;（）;
 

此外，你会过得更好使用的foreach 循环，因为它是一个很大的可读性：

 的foreach（在oOPCList VAR项）
    cboServer.Items.Add（项目）;
 

---

奇怪投率先对象，然后阵列，然后的IEnumerable＆LT ;串＆GT; 通过演员LT;串＆GT; ，是因为以下的需要：

GetOPCServers 返回动态键入。试图访问动态实例以任何方式 - 甚至通过调用的GetType 触发 InvalidCastException的。因此，首先需要将其转换为对象，使其不再是一个动态的类型。在此之后，我们就可以将其转换为阵列，在C＃中唯一支持的方式与非基于零阵列工作。但阵列不强类型化的，所以我们追加调用演员LT;串＆GT; 来得到一个强类型枚举。

I have been assigned to Convert a VB.NET project to C# and I got stuck. I am using a class called RsiOPCAuto, but I don't think that I'll have to go into to much detail into explaining how it works. Let's just get on with my issue.

So basicly what i do is grabbing an object from my class using this code:

public partial class FrmPartialMain : Form
{
    RsiOPCAuto.OPCServer oOpcServer;
    public FrmPartialMain()
    {
        InitializeComponent();
        object RsiOPCAuto;
        object oOPCList;

        oOpcServer = new RsiOPCAuto.OPCServer();
        oOPCList = oOpcServer.GetOPCServers();

So far, so good. By adding a watch I can see that oOPCList now have the value {string[1..4]}.

Now I want to put these four strings into a combo box. I do this with a simple for loop:

for (int i = 0; i <= oOPCList.Length; i++)
{
    cboServer.Items.Add(oOPCList[i]);
}

Edit: Scratch that, changed this to a much nicer foreach loop.

Even though this object now functions as a string array both the oOPCList.Length and (oOPCList[i]) get errors:

.Length: Error 1 'object' does not contain a definition for 'Length' and no extension method 'Length' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?)

oOPCList[i]: Error 2 Cannot apply indexing with [] to an expression of type 'object'

I bet it's the simplest thing but I just can't see it, help is very much appreciated and if there's anything else you need to know be sure to ask :-)

PS. It might be worth mentioning that I have tried some different ways to convert the object to a string array but I continuously get an error telling me that I can not convert system.string[*] to system.string[].

This is the VB.NET code that I am converting:

Friend Class frmPartialMain
    Inherits System.Windows.Forms.Form
        Dim oOpcServer As RsiOPCAuto.OPCServer
        Private Sub frmPartialMain_Load(ByVal eventSender As System.Object, ByVal eventArgs As  System.EventArgs) Handles MyBase.Load
            Dim RsiOPCAuto As Object
            Dim oOPCList() As Object
            Dim i As Integer

            oOpcServer = New RsiOPCAuto.OPCServer
            oOPCList = oOpcServer.GetOPCServers
            For i = LBound(oOPCList) To UBound(oOPCList)
                cboServer.Items.Add(oOPCList(i))
            Next i

解决方案

You need to cast the return value of GetOPCServers to an object first, then to an Array, because this method returns a dynamic type. You can't directly cast to a string[] because strong-typed arrays that are not 0-based are not supported by C#. After the cast, you need to call Cast<string> to get a strong typed enumerable, over which you can iterate:

IEnumerable<string> oOPCList;

oOpcServer = new RsiOPCAuto.OPCServer();
oOPCList = ((Array)(object)oOpcServer.GetOPCServers()).Cast<string>();

Furthermore, you would be better off using a foreach loop, because it is a lot more readable:

foreach(var item in oOPCList)
    cboServer.Items.Add(item);

---

The strange cast first to object, then to Array, and then to IEnumerable<string> via Cast<string> is needed because of the following:

GetOPCServers returns a dynamic type. Trying to access that dynamic instance in any way - even via a call to GetType triggers an InvalidCastException. Therefore, it first needs to be cast to object so it no longer is a dynamic type. After that, we can cast it to an Array, the only supported way in C# to work with non-zero-based arrays. But Array is not strong typed, so we append the call to Cast<string> to get a strong typed enumerable.

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