如何在程序中进一步使用switch语句内分配的变量？

Question

我正在尝试根据当前场景的索引（在Unity术语中）读取不同的文本文件。 因此，我决定使用如下switch语句：

void MyReadString()
{
    Scene currentScene = SceneManager.GetActiveScene(); // Unity command to get the current scene info
    int buildIndex = currentScene.buildIndex; // Unity command to get the current scene number
    string path = string.Empty; // Create an empty string variable to hold the path information of text files
    switch (buildIndex)
    {
        case 0:
            string path = "Assets/Scripts/some.txt"; //It says here that the variable path is assigned but never used!
            break;
        case 1:
            string path = "Assets/Scripts/another.txt"; //Same here - assigned but never used. 
            break;
        // and many other cases - atleast 6 more
    } 
    StreamReader reader = new StreamReader(path); // To read the text file
    // And further string operations here - such as using a delimiter, finding the number of values in the text etc
}

如果我将这一行注释掉：

string path = string.Empty;

然后，

StreamReader reader = new StreamReader(path); // says here the name "path" does not exist in the current context.

我知道这与switch语句的范围有关。 但是，将开关外部的字符串变量声明为“空”是行不通的。 请让我知道是否可以在Switch语句中分配字符串值并稍后使用该值。 或者，如果不可能，请向我建议解决方法。

Answer 1

您遇到了问题，因为您在switch语句中再次重新声明了path变量。 仅在switch语句外部声明一次，然后在switch语句中对其进行分配。

void MyReadString()
{
    Scene currentScene = SceneManager.GetActiveScene(); // Unity command to get the current scene info
    int buildIndex = currentScene.buildIndex; // Unity command to get the current scene number
    string path = null;
    // Create an empty string variable to hold the path information of text files
    switch (buildIndex)
    {
        case 0:
            path = "Assets/Scripts/some.txt"; //It says here that the variable path is assigned but never used!
            break;
        case 1:
            path = "Assets/Scripts/another.txt"; //Same here - assigned but never used. 
            break;
            // and many other cases - atleast 6 more
    }
    StreamReader reader = new StreamReader(path); // To read the text file                                               // And further string operations here - such as using a delimiter, finding the number of values in the text etc
}

---

无关，但请注意，这不是在Unity中读取文件的方式。构建项目时，该代码将失败。 使用资源API或使用Assetbundles 。

Answer 2

您正在尝试重新声明一个变量-但实际上您只想向在此声明的现有变量分配一个新变量：

// This line is still needed, and must be before the switch statement.
// Ideally, remove the initialization - your switch statement should cover
// all cases, I expect.
string path = string.Empty;

所以这：

case 0:
    string path = "Assets/Scripts/some.txt"; //It says here that the variable path is assigned but never used!
    break;
case 1:
    string path = "Assets/Scripts/another.txt"; //Same here - assigned but never used. 
    break;

应该：

case 0:
    path = "Assets/Scripts/some.txt";
    break;
case 1:
    path = "Assets/Scripts/another.txt";
    break;

IMO会比较干净，要么将此逻辑放在单独的方法中，要么仅具有数组或Dictionary<int, string> 。 例如：

string path = GetScriptPath(buildIndex);

或（其scriptPaths为string[]或Dictionary<int, string> ）

string path = scriptPaths[buildIndex];

Answer 3

您对范围位是正确的。 在switch语句中声明的变量路径使其只能从该语句中访问。 为了使您可以从语句外部访问变量，必须在更大的范围内声明它。

如果要访问该变量：

• 仅在该函数中 ，在void MyReadString（）中但在switch语句之外声明它
• 在类中的其他地方，在类结构中声明它（在MyReadString（）函数之外），如果您以后想在其他函数中使用该路径，则可以使用它

在当前形式下，每次switch语句遇到大小写时，您都在创建一个新字符串，通过移动声明，您将只分配一个预先声明的字符串。