迭代字典键/值对，其中值是数组

Question

I am trying to display the elements of a key/value pair from a dictionary where the value is an array. It is a dictionary of usernames where the key is a string representing the name of the user and the values are the users attributes. I want each key/value pair to be listed together, so the output would be like this:

User1 (Key)
User1_email
user1_fullName
User1_displayName

User2 (Key)
User2_email
user2_fullName
User2_displayName
etc...

However, the result I am getting is that it is displaying the correct key but only the last elements of the value are being displayed. For example, here is the output I am getting:

User1 (Key)
User2_email
user2_fullName
User2_displayName

User2 (Key)
User2_email
user2_fullName
User2_displayName
etc...

Here is my foreach loop:

foreach (KeyValuePair<string, string[]> entry in userNames)
{
    txtOutput.Text += entry.Key;
    foreach (string value in entry.Value)
    {
        txtOutput.Text += value + Environment.NewLine;
    }
}

The nested foreach loop seems to be iterating over ALL of the values regardless of the key, but I only want it to iterate over the values associated with the CURRENT key in the parent foreach loop. Hope my question makes sense, any help is appreciated.

Thank you,

Answer 1

You gave the following code in a comment for populating your dictionary:

string[] tempArray = new string[5];

for (int i = 0; i < rows; i++)
{
    for (int j = 0; j < 6; j++)
    {
        if (j != 0) tempArray[j-1] = userInfo[i, j];
    }
    userNames.Add(userInfo[i, 0], tempArray);
}

It looks like you were hoping to reduce memory usage by using a single array outside the for loop. However, this has an unexpected side-effect on your dictionary!

Dictionaries will store arrays by reference. On the first iteration of the populating loop, you call usernames.Add(..., tempArray) which assigns tempArray instance to the first user key. Then the second iteration re-uses the same array and assigns it to the next user key. Since you are not initializing a new array instance for each user, you are actually associating all of your keys with the same array. The final iteration of the loop will determine the state of this array.

This should fix it:

for (int i = 0; i < rows; i++)
{
    string[] tempArray = new string[5];
    for (int j = 0; j < 6; j++)
    {
        if (j != 0) tempArray[j-1] = userInfo[i, j];
    }
    userNames.Add(userInfo[i, 0], tempArray);
}