C# 为什么有些变量采用新的形式i'；我得到警告说他们从未被分配？

这是新表单的顶部：

namespace test
{
    public partial class Youtube_Uploader : Form
    {
        public class ComboboxItem
        {
            public string Text { get; set; }
            public object Value { get; set; }

            public override string ToString()
            {
                return Text;
            }
        }

        YouTubeService service;
        string devKey = "";
        string apiKey = "";";
        string userName = "";
        string Password = "";
        string feedUrl = "";
        string FileNameToUpload = "";
        string[] stringProgressReport = new string[5];
        long totalBytes = 0;
        DateTime dt;
        Upload upload;

        public Youtube_Uploader()
        {
            InitializeComponent();

            service = AuthenticateOauth(apiKey);
            var videoCatagories = service.VideoCategories.List("snippet");
            videoCatagories.RegionCode = "IL";
            var result = videoCatagories.Execute();
            for (int i = 0; i < result.Items.Count; i++)
            {
                ComboboxItem item = new ComboboxItem();
                item.Text = result.Items[i].Snippet.Title;
                item.Value = result.Items[i].Id;
                upload.comboBox1.Items.Add(item);
            }
            upload.comboBox1.SelectedIndex = 0;
            MakeRequest();
        }

我没有犯错误。没有例外。 我只是想知道我得到这个警告是不是一件坏事？

---

我对upload var所做的一切就是访问upload表单的控件。

以下是一个简单示例中可以做和不能做的事情：

void Main()
{
    Foo f1 = new Foo("good",6);
    Foo f2;
    string temp_string;

    // You can do this
    temp_string = f1.S;
    // Bot not this
    // temp_string = f2.S; --> Use of unassigned local variable 'f2'

    // You can also do this: 
    int temp_int = Foo.I;
    // But  not
    // temp_int = f1.I; 

    // You can do
    bool b = TestFoo(f1);
    // But not
    // b = TestFoo(f2); --> Use of unassigned local variable 'f2'
}

public class Foo {
    // static class property, can be accessed with "Foo.I"
    public static int I {get; set;}

    // instance property, can be accessed with "f1.S"
    public string S { get; set; }

    public Foo(string s, int i = 0) {
        S = s;
        I = i;
    }
}

public bool TestFoo(Foo foo) {
    return foo != null;
}

---

您从未将

upload

设置为任何内容。@TonyLee实际上，您会得到一个编译错误，说

Member'upload.comboBox1'不能通过实例引用访问；改用类型名称限定它

。

void Main()
{
    Foo f1 = new Foo("good",6);
    Foo f2;
    string temp_string;

    // You can do this
    temp_string = f1.S;
    // Bot not this
    // temp_string = f2.S; --> Use of unassigned local variable 'f2'

    // You can also do this: 
    int temp_int = Foo.I;
    // But  not
    // temp_int = f1.I; 

    // You can do
    bool b = TestFoo(f1);
    // But not
    // b = TestFoo(f2); --> Use of unassigned local variable 'f2'
}

public class Foo {
    // static class property, can be accessed with "Foo.I"
    public static int I {get; set;}

    // instance property, can be accessed with "f1.S"
    public string S { get; set; }

    public Foo(string s, int i = 0) {
        S = s;
        I = i;
    }
}

public bool TestFoo(Foo foo) {
    return foo != null;
}