Breaking/exit nested for in vb.net

问题:

How do I get out of nested for or loop in vb.net?

I tried using exit for but it jumped or breaked only one for loop only.

How can I make it for the following:

for each item in itemList
     for each item1 in itemList1
          if item1.text = "bla bla bla" then
                exit for
          end if
     end for
end for

回答1:

Unfortunately, there's no exit two levels of for statement, but there are a few workarounds to do what you want:

• Goto. In general, using goto is considered to be bad practice (and rightfully so), but using goto solely for a forward jump out of structured control statements is usually considered to be OK, especially if the alternative is to have more complicated code.

  For Each item In itemList
      For Each item1 In itemList1
          If item1.Text = "bla bla bla" Then
              Goto end_of_for
          End If
      Next
  Next
  
  end_of_for:
  

• Dummy outer block

  Do
      For Each item In itemList
          For Each item1 In itemList1
              If item1.Text = "bla bla bla" Then
                  Exit Do
              End If
          Next
      Next
  Loop While False
  

  or

  Try
      For Each item In itemlist
          For Each item1 In itemlist1
              If item1 = "bla bla bla" Then
                  Exit Try
              End If
          Next
      Next
  Finally
  End Try
  

• Separate function: Put the loops inside a separate function, which can be exited with return. This might require you to pass a lot of parameters, though, depending on how many local variables you use inside the loop. An alternative would be to put the block into a multi-line lambda, since this will create a closure over the local variables.

• Boolean variable: This might make your code a bit less readable, depending on how many layers of nested loops you have:

  Dim done = False
  
  For Each item In itemList
      For Each item1 In itemList1
          If item1.Text = "bla bla bla" Then
              done = True
              Exit For
          End If
      Next
      If done Then Exit For
  Next
  

回答2:

Put the loops in a subroutine and call return

回答3:

I've experimented with typing "exit for" a few times and noticed it worked and VB didn't yell at me. It's an option I guess but it just looked bad.

I think the best option is similar to that shared by Tobias. Just put your code in a function and have it return when you want to break out of your loops. Looks cleaner too.

For Each item In itemlist
    For Each item1 In itemlist1
        If item1 = item Then
            Return item1
        End If
    Next
Next

回答4:

Make the outer loop a while loop, and "Exit While" in the if statement.

回答5:

For i As Integer = 0 To 100
    bool = False
    For j As Integer = 0 To 100
        If check condition Then
            'if condition match
            bool = True
            Exit For 'Continue For
        End If
    Next
    If bool = True Then Continue For
Next