C#切换案例使用循环外的变量[关闭]答案

【问题标题】：C# Switch case use variable out of loop [closed]C#切换案例使用循环外的变量[关闭]
【发布时间】：2020-08-19 13:09:02
【问题描述】：

所以我遇到的问题是我有一个循环，循环中有一个 switch 语句。我在循环中声明了变量，但在 switch 语句之外。如何将其导入 switch 语句？

例子：

for (int i = 1; i < 3; i++)
{
    var detectionid = detectionResult.Sequence.Items[i];
    ulong trackId = detectionid.TrackId;

    switch (i)
    {
        case 1:
            Console.WriteLine(trackId);
            break;
        case 2:
            Console.WriteLine(trackId);
            break;
        default:
            Console.WriteLine("Default case");
            break;
    }
}

所以trackId 是我想使用的变量。但是由于某种原因它不起作用，它一直说我必须声明这个变量。

PS：我是 C# 的初学者，所以我的知识很少。

编辑：这是我的完整源代码

 private void OnDetect(CallbackEventArgument callbackArgument)
    {
        if (cameraTemp > 35)
        {
           

            var detectionResult = callbackArgument.GetDetectionResult();
           // var firstDetection = detectionResult.Sequence.Items[0];
           
                foreach (var detection in detectionResult.Sequence.Items)
                {

                    var message = string.Empty;



                

               ImageArgument fullSizeImage = null;
                    switch (detectionResult.Type)
                    {
                        case T3DDetectionType.OBSERVATION:
                            message = "Track ID: " + detection.TrackId;
                            fullSizeImage = detectionResult.RGBImage;
                            break;
                        case T3DDetectionType.DEPTH_LIVENESS:
                        case T3DDetectionType.THERMAL_LIVENESS:
                            message = "Track ID: " + detection.TrackId + " Score: " + (detection as Liveness).Score.ToString("N0");
                            

                            score = (detection as Liveness).Score.ToString("N0");
                            fullSizeImage = detectionResult.FullImage;



                            break;
                        case T3DDetectionType.TEMPERATURE:
                            message = "Temperature: " + (detection as Temperature).MeasurementValueCelsius.ToString("N1") + "°C";
                        temperature = (detection as Temperature).MeasurementValueCelsius.ToString("N1") + "°C";
                        //float temperature = (detection as Temperature).MeasurementValueCelsius;
                        fullSizeImage = detectionResult.FullImage;

                       


                        break;

                    }



                for (int i = 0; i < detectionResult.Sequence.Items.Count(); i++)
                {
                    var detectionid = detectionResult.Sequence.Items[i];
                    double depth = detectionid.Depth/1000.00 ;
                    ulong trackId = detectionid.TrackId;

                    switch (i)
                    {
                        case 0:

                            

                            StringBuilder sb = new StringBuilder();
                            StringWriter sw = new StringWriter(sb);
                            /* https://www.newtonsoft.com/json/help/html/WriteJsonWithJsonTextWriter.htm */
                            using (JsonWriter writer = new JsonTextWriter(sw))
                            {
                                writer.Formatting = Formatting.Indented;


                                writer.WritePropertyName(trackId.ToString());
                                writer.WriteStartArray();
                                writer.WriteStartObject();
                                writer.WritePropertyName("Temperature");
                                writer.WriteValue(temperature);
                                writer.WritePropertyName("Depth");
                                writer.WriteValue(depth);
                                writer.WritePropertyName("TrackId");
                                writer.WriteValue(trackId);
                                writer.WriteEndObject();
                                writer.WriteEnd();
                            }
                            System.IO.File.AppendAllText(@"C:/Users/Kimeru/Documents/Dermalog Noah WPF/data" + trackId + ".json", sb.ToString());
                            break;

                        case 1:
                           
                            break;
                        

                        case 2:
                            
                            break;
                        case 3:
                            Console.WriteLine("Case 2");
                            break;
                        case 4:
                            Console.WriteLine("Case 2");
                            break;
                        case 5:
                            Console.WriteLine("Case 2");
                            break;
                        case 6:
                            Console.WriteLine("Case 2");
                            break;
                        default:
                            Console.WriteLine("Default case");
                            break;
                    }
                }




                ClearDetectCanvas(detectionResult.Type);
                    UpdateDetectImages(fullSizeImage, detection.Portrait);
                    UpdateDetectCanvas(fullSizeImage, detection);
                    UpdateLabel(detectionResult.Type, message);

                    var trackIDs = callbackArgument.GetTrackIDs().ToList();
                    if (trackIDs.Count > 0)
                    {
                        UpdateTrackStatus(callbackArgument.GetDetectionItemsForTrack(trackIDs.First()));
                    }

                }
            }
        
    }

【问题讨论】：

用var代替double ulong。
我的代码粘贴错误，我改了！
现在您已经修复了类型，代码似乎没有任何问题。如果你只做ulong trackId = 5;，你能重现这个问题吗？你也可以包括你得到的确切错误。
还是不行，它说“在声明之前不能使用局部变量'trackId'”
您似乎省略了一些重现问题所需的代码。如果您从ulong trackId = detectionid.TrackId; 行向后搜索，您会发现trackId 的另一个匹配项吗？

标签： c# variables switch-statement

【解决方案1】：

没有double ulong 类型。

double 是 floating point type
ulong 是 integral numeric type

使用正确的类型或使用var 让编译器推断类型。

var trackId = detectionid.TrackId;

【讨论】：

【解决方案2】：

这里的问题在于trackId的声明。您应该使用 ulong 或 double，而不是同时使用两者。

            for (int i = 1; i < 3; i++)
            {
                var detectionid = detectionResult.Sequence.Items[i];
                ulong trackId = detectionid.TrackId;
                // or
                //double trackId = detectionid.TrackId;
                // or
                //var trackId = detectionid.TrackId;
                switch (i)
                {
                    case 1:
                        Console.WriteLine(trackId);
                        break;
                    case 2:
                        Console.WriteLine(trackId);
                        break;
                    default:
                        Console.WriteLine("Default case");
                        break;
                }
            }

【讨论】：