c＃检查标签，如果它包含一个字符串

Question

我试图做一个按钮以不同'行动'。 当我第一次点击你应该看到桌面名称，第二次点击应该删除这个。 但我的第二个代码显示了我第一次点击，我做错了什么？

string userName = System.Security.Principal.WindowsIdentity.GetCurrent().Name; 
     lbUsername.Text = "Username: Hallo," + userName; 

     if (lbUsername.Text.Contains(userName)) 
     { 
      lbUsername.Text = "klik op de knop, dokus."; 
     } 

Answer 1

它恰克到：适用于标签的文本

string userName = System.Security.Principal.WindowsIdentity.GetCurrent().Name; 

if (lbUsername.Text.Contains(userName)) 
{ 
    lbUsername.Text = "klik op de knop, dokus."; 
} 
else 
{ 
    lbUsername.Text = "Username: Hallo," + userName; 
} 

的更改会立即传播。

Answer 2

您的lblUsername.Text赋值都将始终执行，因为if条件将始终评估为true。

请尝试此操作。

string userName = System.Security.Principal.WindowsIdentity.GetCurrent().Name; 
if (lbUsername.Text.Contains(userName)) 
{ 
    lbUsername.Text = "klik op de knop, dokus."; 
} 
else 
{ 
    lbUsername.Text = "Username: Hallo," + userName; 
} 

，或者如果您使用的是Conditional Operator：

bool hasUserName = lbUsername.Text.Contains(userName)) 
lbUsername.Text = hasUserName ? "klik op de knop, dokus." : "Username: Hallo," + userName; 

编辑：

基于贴在dotnetFiddle link的代码，你应该这样做。在Form_Load事件上分配lblUsername的初始值。在按钮上单击可以始终分配用户名文本

private void Form1_Load(object sender, EventArgs e) 
    { 
     //THis will only be assigned when the Form is loaded. 
     lbUsername.Text = "klik op de knop, dokus."; 
    } 

    private void btnMagic_Click(object sender, EventArgs e) 
    { 
     //On Every button click this will be executed. 
     string userName = System.Security.Principal.WindowsIdentity.GetCurrent().Name; 
     lbUsername.Text = "Username: Hallo," + userName; 

    }