使用參數方法的ThreadStart

Question

我正在嘗試在.Net中學習線程。

很多的你一定已經看到了這一點：

private void button1_Click(object sender, EventArgs e) 
{ 
    Thread t = new Thread(new ThreadStart(loop)); 
    t.Start(); 
} 

private void loop() 
{ 
    for (int i = 0; i < 100000; i++) 
    { 
     textBox1.Text = i.ToString(); 
    } 
} 

它工作正常，但如果我的循環方法的參數在裏面，如：

private void loop(string str) 
{ 
    for (int i = 0; i < 100000; i++) 
    { 
     textBox1.Text = i + str; 
    } 
} 

那麼如何調用該方法我的ThreadStart作爲ThreadStart只接受方法名稱。那麼如何在不同的線程中調用循環方法？

Answer 1

Thread t = new Thread(new ParameterizedThreadStart(loop)); 
t.Start("Hello world"); 

private void loop(object obj) 
{ 
    string str = (string)obj; 

    for (int i = 0; i < 100000; i++) 
    { 
     // Don't do this: you can't change a control from another thread. Danger Will Robinson! 
     textBox1.Text = i + str; 
    } 
} 

注意，loop方法必須接受object參數，所以你必須給object上溯造型到你的類型。如果你不想，你可以使用閉包和匿名方法：

string str = "Hello world"; 
Thread t = new Thread(() => { 
    for (int i = 0; i < 100000; i++) 
    { 
     // Don't do this: you can't change a control from another thread. Danger Will Robinson! 
     textBox1.Text = i + str; 
    } 
}); 
t.Start(); 

這樣的匿名方法將「關閉」，圍繞str，這將是相似彷彿你已通過參數。 類似，因爲關閉變量存在差異/問題。在現實中，我會寫類似的東西：

string str = "Hello world"; 

{ 
    string str2 = str; 

    Thread t = new Thread(() => { 
     for (int i = 0; i < 100000; i++) 
     { 
      // Don't do this: you can't change a control from another thread. Danger Will Robinson! 
      textBox1.Text = i + str2; 
     } 
    }); 

    t.Start(); 
} 

，這樣沒有人可以「觸摸」 str2。

如果你需要我可以找到所以一些答案來解釋這個「問題」

Answer 2

你會使用ParameterizedThreadStart代替：http://msdn.microsoft.com/en-us/library/system.threading.parameterizedthreadstart.aspx

Thread t = new Thread(new ParameterizedThreadStart(loop)); 
t.Start("Foo"); 

// Note the use of Object here to match the delegate signature 
private void loop(Object state) 
{ 
    var str = state as String; 
    for (int i = 0; i < 100000; i++) 
    { 
     // For what it is worth, this is illegal: 
     // textBox1.Text = i + str; 
     // You need to Invoke back to the UI thread to access a control's properties: 
     textBox1.Invoke(()=> { textBox1.Text = i + str; }); 
    } 
} 

Answer 3

有一個ParameterizedThreadStart類，它使用一個參數代表可以投實例化一個線程時：

private void button1_Click(object sender, EventArgs e) 
{ 
    Thread t = new Thread(new ParameterizedThreadStart(loop)); 
    t.Start(str); 
} 

private void loop(string str) 
{ 
    for (int i = 0; i < 100000; i++) 
    { 
     //the code you had is a no-no when you are multithreading; 
     //all UI updates must occur on the main thread 
     //textBox1.Text = i + str; 
     UpdateTextBoxText(textBox1, i+str); 
    } 
} 

private void UpdateTextBoxText(TextBox textBox, string text) 
{ 
    //the method will invoke itself on the main thread if it isn't already running there 
    if(InvokeRequired) 
    { 
     this.Invoke((MethodInvoker)(()=>UpdateTextBoxText(TextBox textBox, string text))); 
     return; 
    } 

    textBox.Text = text; 
} 

如果你不」 t需要對線程啓動和停止時的細粒度控制，可以將其留給ThreadPool並使用Delegate.BeginInvoke：

private void button1_Click(object sender, EventArgs e) 
{ 
    Action<string> method = loop; 

    method.BeginInvoke(str, null, null); 
} 

private void loop(string str) 
{ 
    for (int i = 0; i < 100000; i++) 
    { 
     //textBox1.Text = i + str; 
     UpdateTextBoxText(textBox1, i+str); 
    } 
} 

private void UpdateTextBoxText(TextBox textBox, string text) 
{ 
    //the method will invoke itself on the main thread if it isn't already running there 
    if(InvokeRequired) 
    { 
     this.Invoke((MethodInvoker)(()=>UpdateTextBoxText(textBox, text))); 
     return; 
    } 

    textBox.Text = text; 
} 

Answer 4

像這樣：

new Thread(() => loop("MyString")).Start(); 

你甚至不必用的ThreadStart/ParameterizedThreadStart一塌糊塗。

Answer 5

看看ParameterizedThreadStart，它允許您將參數傳遞到您的線程啓動功能。