将void转换为字符串 - void对象问题？

Question

我有以下多线程代码，它采取服务器列表和异步运行繁重的操作，繁重的操作返回结果，并试图填充多行文本框的结果（作为批处理完成或作为每个任务返回），我已经添加了一些代码，希望执行这项任务，但下面三行与正确的意见导致我们混淆关于无效静态和无效的对象:(任何提示大大收到我需要改变.. ..谢谢

这里是代码： -

public partial class Form1 : Form 
{ 
    Progress<string> progressReporter = new Progress<string>(); 
    CancellationTokenSource cancelSource; 

    public Form1() 
    { 
     InitializeComponent(); 
     progressReporter.ProgressChanged += progressManager_ProgressChanged; 
    } 

    async private void btnStart_Click(object sender, EventArgs e) 
    { 
     btnStart.Enabled = false; 
     btnCancel.Enabled = true; 
     cancelSource = new CancellationTokenSource(); 
     textBox1.Text = await Task.Run(() => PerfromTaskAction(cancelSource.Token), cancelSource.Token); //--Cannot implicity convert type 'void' to 'string' 
     await Task.Run(() => PerfromTaskAction(cancelSource.Token), cancelSource.Token); 
     lblStatus.Text = "Completed."; 
     btnStart.Enabled = true; 
     btnCancel.Enabled = false; 
    } 
    static async Task PerfromTaskAction(CancellationToken ct) 
    { 
     StringBuilder sb = new StringBuilder(); 

     object[] arrObjects = new object[] { "SERVER1", "SERVER2", "SERVER3", "SERVER4" }; 
     IList<Task> tasks = new List<Task>(); 
     foreach (object i in arrObjects) 
     { 
      if (ct.IsCancellationRequested) break; 
      sb.Append(string.Format("{0}", tasks.Add(Task.Run(() => HeavyOperation(i.ToString()))))); //-- Argument 2: cannot convert from 'void' to 'object' 
      tasks.Add(Task.Run(() => HeavyOperation(i.ToString()))); 
     } 
     await Task.WhenAll(tasks).ConfigureAwait(false); 
     return sb.ToString(); //--Since 'Form1.PerfromTaskAction(CancellationToken)' is an async method that returns 'Task', a return keyword must not be followed by an object expression? 
    } 
    void progressManager_ProgressChanged(object sender, string e) 
    {   
     lblStatus.Invoke((Action)(() => lblStatus.Text = e)); 
    } 
    static string HeavyOperation(string i) 
    { 
     PowerShell ps = PowerShell.Create(); 
     ps.AddCommand("invoke-command"); 
     ps.AddParameter("computername", i); 
     ps.AddParameter("scriptblock", ScriptBlock.Create("get-vmreplication | select State")); 
     Collection<PSObject> result = ps.Invoke(); 
     return(result[0].Properties["State"].Value.ToString()); 
    } 
    private void btnCancel_Click(object sender, EventArgs e) 
    { 
     cancelSource.Cancel(); 
    } 

} 

Answer 1

你有三个错误，所以把他们一次一个：

//-- Argument 2: cannot convert from 'void' to 'object' 
sb.Append(string.Format("{0}", tasks.Add(Task.Run(() => HeavyOperation(i.ToString()))))); 

的List<T>.Add返回类型是void。所以它不能用作string.Format的第二个参数。这里一点都不清楚你在想用来处理这行代码，所以我不能建议修复。

//--Since 'Form1.PerfromTaskAction(CancellationToken)' is an async method that returns 'Task', a return keyword must not be followed by an object expression 
return sb.ToString(); 

此错误是说你在async Task方法（这是异步相当于void的）的时候，所以它不能有返回值。然而你的代码试图返回一个值。

这里的修复方法就是改变方法签名返回Task<string>：

static async Task<string> PerfromTaskAction(CancellationToken ct) 

至于最后的错误：

//--Cannot implicity convert type 'void' to 'string' 
textBox1.Text = await Task.Run(() => PerfromTaskAction(cancelSource.Token), cancelSource.Token); 

如果PerformTaskAction返回Task，那么Task.Run(() => PerfromTaskAction(cancelSource.Token), cancelSource.Token)返回类型为也Task，这意味着await Task.Run(() => PerfromTaskAction(cancelSource.Token), cancelSource.Token)的类型是void。并且您不能采取void并将其分配给textBox1.Text。

修复了最后一个错误（更改为Task<string>）也修复了这一错误。返回类型Task.Run(() => PerfromTaskAction(cancelSource.Token), cancelSource.Token)现在是Task<string>，await Task.Run(() => PerfromTaskAction(cancelSource.Token), cancelSource.Token)的类型现在是string。

从评论更新：

既然你想返回所有的字符串时，他们都齐全，这是比较容易做不StringBuilder：

static async Task<string> PerfromTaskAction() 
{ 
    object[] arrObjects = new object[] { "SERVER1", "SERVER2", "SERVER3", "SERVER4" }; 
    var tasks = arrObjects.Select(i => Task.Run(() => HeavyOperation(i.ToString()))); 
    var results = await Task.WhenAll(tasks).ConfigureAwait(false); 
    return string.Join("", results); 
} 

注意，因为CancellationToken ISN” t用于HeavyOperation，它可以从PerformTaskAction签名中删除。

Answer 2

改变方法签名

static async Task<string> PerfromTaskAction(CancellationToken ct) 

return Task(sb.ToString()); 

然后

textBox1.Text = await Task.Run(() => PerfromTaskAction(cancelSource.Token), cancelSource.Token).Result;