vb.net 防止列表框重复
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Prevent Listbox Duplicates
提问by user2980316
Okay, newbie question here. I'm creating a random key generator which will generate keys from a string, and add each key combination to a Listbox. My question is how would I be able to prevent duplicates from appearing/being added to the listbox thus preventing duplicate keys. Currently the key is generated into 5 separate sections and is then (crudely) brought together into an invisible textbox for temp storage before it's added into the listbox1.
好的，新手问题在这里。我正在创建一个随机密钥生成器，它将从字符串生成密钥，并将每个组合键添加到列表框。我的问题是如何防止重复项出现/添加到列表框中，从而防止重复项。目前，密钥被生成为 5 个单独的部分，然后（粗略地）在将其添加到列表框之前将其组合到一个不可见的文本框中以进行临时存储。
generatetextonlycode = strName
TextBox1.Text = Key1.Text & "-" & Key2.Text & "-" & Key3.Text & "-" & Key4.Text & "-" & Key5.Text`
I know this is a really bad way to go about it, but it's easy and works -- Only it is prone to duplicates ;( This code obviously will go into a Loop statement once it works. Here's the full thing:
我知道这是一个非常糟糕的方法，但它很容易并且有效——只是它容易重复；(这段代码显然一旦起作用就会进入循环语句。这是完整的：
Private Sub Generatebtn_Click(sender As Object, e As EventArgs) Handles Generatebtn.Click
Key2.Text = generatetextonlycode()
Key3.Text = generatetextonlycode()
Key4.Text = generatetextonlycode()
Key5.Text = generatetextonlycode()
End Sub
Public Function generatetextonlycode() As Object
Dim intRnd As Object
Dim strName As Object
Dim intNameLength As Object
Dim intLenght As Object
Dim strInputString As Object
Dim inStep As Object
strInputString = "1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ"
intLenght = Len(strInputString)
intNameLength = 5
Randomize()
strName = ""
For inStep = 1 To intNameLength
intRnd = Int((intLenght * Rnd()) + 1)
strName = strName & Mid(strInputString, intRnd, 1)
Next
generatetextonlycode = strName
TextBox1.Text = Key1.Text & "-" & Key2.Text & "-" & Key3.Text & "-" & Key4.Text & "-" & Key5.Text
'
'
'THIS IS WHERE I'D LIKE TO ADD THE CONTENTS OF Textbox1 INTO Listbox1 IF THE LISTBOX DOESNT ALREADY CONTAIN THE KEY!
'
'
End Function
(Note that Key1.text contains a static value so that all keys start of the same. I'm using visual basic with .net 4.5)
（请注意， Key1.text 包含一个静态值，因此所有键都以相同的方式开始。我在 .net 4.5 中使用了visual basic）
回答by Karl Anderson
Use the list box's Contains()method to test if the value is already in the list box or not, like this:
使用列表框的Contains()方法来测试值是否已经在列表框中，像这样：
If Not listBox1.Items.Contains(TextBox1.Text) Then
' It is not already in the list box so add it
ListBox1.Items.Add(TextBox1.Text)
End If
A more efficient approach is to use a .NET collection that does not allow duplicates (i.e. HashSet<T>).
更有效的方法是使用不允许重复的 .NET 集合（即HashSet<T>）。
Per MSDN:
根据 MSDN：
The HashSet class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order.
HashSet 类提供高性能的集合操作。集合是不包含重复元素且其元素没有特定顺序的集合。
Note: HashSet<T>.Add()method returns a Boolean(Trueif the item was added to the collection and Falseif the item is already present).
注意：HashSet<T>.Add()方法返回 a Boolean(True如果项目已添加到集合中并且False项目已经存在)。
So your code could be this:
所以你的代码可能是这样的：
Dim theValues As New HashSet(Of String)
Dim success As Boolean = theValues.Add(TextBox1.Text)
' Was the addition of the string successful or not?
If success Then
' Yes, so re-bind the list box
End If
