checking to see if DDL value exists

Discussion in 'ASP .Net' started by Darrel, Dec 10, 2004.

  1. Darrel

    Darrel Guest

    I'm trying to add an extra layer of error checking on a Drop Down List. The
    list is populated from one table, and then I select the selectedValue from
    another DB.

    While it SHOULDN'T ever happen, just incase, I want to check that the
    selected value actually exists as a value in the dropDownList before I
    actually try to select it.

    I've tried this:

    if
    (DropDownList_category1.Items.FindByValue(ds.Tables(0).Rows(0)("listingCategory1")).Value.ToString
    = "") then...

    But that just gives me a " Object reference not set to an instance of an
    object. " error.

    -Darrel
     
    Darrel, Dec 10, 2004
    #1
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  2. What you would probably want to do is do the checking against the
    dataset before you actually do the binding. Even if the selected value
    doesn't exist, I'm not sure that anything will happen other than nothing
    will be selected. You could easily test this by manually setting the
    selectedvalue to something that you know does not exist.

    Lowell
     
    Lowell Heddings, Dec 10, 2004
    #2
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  3. Darrel

    Darrel Guest

    What you would probably want to do is do the checking against the dataset
    Well, the catch is if the item doesn't exist, I actually want it to select a
    differerent item.

    As for checking in the dataset, I'm still not quite sure how to go about
    that. I could grab the list of categories from table1 and put it in an
    array, then, when I grab the record from table2, I could compare the
    pertinent field with that array. I'm trying to come up with a simpler
    solution though.

    Let me sleep on it ;o)

    -Darrel
     
    Darrel, Dec 10, 2004
    #3
  4. Hi,

    before this code

    if
    (DropDownList_category1.Items.FindByValue(ds.Tables(0).Rows(0)("listingCategory1")).Value.ToString
    = "") then...

    add

    if DropDownList_category1.Items.count > 0 then

    remember to add the "End If" tag if you are in VB.NET

    hope it helps

    weichung

    hope
     
    weichung[MCSD,MCDBA], Dec 10, 2004
    #4
  5. Darrel

    darrel Guest

    add

    I don't think I'm quite explaining this correctly. Let's say my DDL has the
    following value options:

    3
    4
    5
    8
    9
    12
    0

    These would be all the active options pulled from Table 1.

    Then, in table 2, I grab the data for a specific record, who's foreign key
    for Table 1 is '2'.

    Since 2 doesn't exist as an option in the DDL, I can't select it. So,
    instead, I want to select '0'.

    However, all this said, I'm thinking there really should be no reason to do
    this error checking here. I really need to spot the problem prior to this
    step. That said, I am curious if there is a simple way to see if a DDL.item
    exists.

    -Darrel
     
    darrel, Dec 10, 2004
    #5
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