Get dictionary value by key

Question

How can I get the dictionary value by a key on a function?

My function code (and the command I try doesn't work):

static void XML_Array(Dictionary<string, string> Data_Array)
{
    String xmlfile = Data_Array.TryGetValue("XML_File", out value);
}

My button code:

private void button2_Click(object sender, EventArgs e)
{
    Dictionary<string, string> Data_Array = new Dictionary<string, string>();
    Data_Array.Add("XML_File", "Settings.xml");

    XML_Array(Data_Array);
}

I want on the XML_Array function the variable to be:

string xmlfile = "Settings.xml":

Solution 1

It's as simple as this:

String xmlfile = Data_Array["XML_File"];

Note that if the dictionary doesn't have a key that equals "XML_File", that code will throw an exception. If you want to check first, you can use TryGetValue like this:

string xmlfile;
if (!Data_Array.TryGetValue("XML_File", out xmlfile)) {
   // the key isn't in the dictionary.
   return; // or whatever you want to do
}
// xmlfile is now equal to the value

Solution 2

Just use the key name on the dictionary. C# has this:

 Dictionary<string, string> dict = new Dictionary<string, string>();
 dict.Add("UserID", "test");
 string userIDFromDictionaryByKey = dict["UserID"];

If you look at the tip suggestion:

Solution 3

That is not how the TryGetValue works. It returns true or false based on whether the key is found or not, and sets its out parameter to the corresponding value if the key is there.

If you want to check if the key is there or not and do something when it's missing, you need something like this:

bool hasValue = Data_Array.TryGetValue("XML_File", out value);
if (hasValue) {
    xmlfile = value;
} else {
    // do something when the value is not there
}

Solution 4

Dictionary<String, String> d = new Dictionary<String, String>();
d.Add("1", "Mahadev");
d.Add("2", "Mahesh");
Console.WriteLine(d["1"]); // It will print Value of key '1'

Solution 5

static void XML_Array(Dictionary<string, string> Data_Array)
{
    String value;
    if(Data_Array.TryGetValue("XML_File", out value))
    {
        // ... Do something here with value ...
    }
}

View more solutions

Comments

[Peter Mortensen]

Re "the command I try doesn't work": What happens? What are the symptoms?

[Ladislav Ondris]

It throws an exception if the key does not exist. That is why other people's answers suggest that you should use TryGetValue.

[FrenkyB]

I don't think this is the reason that others are suggesting TryGetValue. My solution is simplification, which I was not aware of. When I've found it out, I've pasted it here. And it seems that a lot of others didn't know about that also. Otherwise, they could also paste this answer and add that throws exception if key doesn't exist. Anyway, thanks for warning.

[Ortund]

For some reason I always forget this with Dictionaries... Like it doesn't seem like it should be this straightforward.

[Koenman]

Still a good solution when you know that values will always exiist. If not, it would still recommend the answers that suggest using TryGetValue().

[BDL]

This would search for the key twice in the dictionary. Why not use the out parameter of TryGetValue instead of searching a second time? Even with your code: Why even use TryGetValue instead of ContainsKey if you want to go that route?

[Peter Mortensen]

How does that answer the question? "How can I get the dictionary value by a key" An explanation would be in order. E.g., what is the idea/gist? Please respond by editing (changing) your answer, not here in comments (without "Edit:", "Update:", or similar - the answer should appear as if it was written today).

[Peter Mortensen]

Is this the answer to a different question?

[Peter Mortensen]

An explanation would be in order. E.g., what is the idea/gist? What was changed? What was the fix? Please respond by editing (changing) your answer, not here in comments (without "Edit:", "Update:", or similar - the answer should appear as if it was written today).

[Peter Mortensen]

There isn't anyone here by the name "dasblinkenlight". What answer does it refer to?

[Peter Mortensen]

An explanation would be in order. E.g., what is the idea/gist? Please respond by editing (changing) your answer, not here in comments (without "Edit:", "Update:", or similar - the answer should appear as if it was written today).

[Peter Mortensen]

You have got some explaining to do. (But without "Edit:", "Update:", or similar - the answer should appear as if it was written today).

[The incredible Jan]

I have no use for hasValue : if (Data_Array.TryGetValue("XML_File", out value)) { xmlfile = value; } else { // do something when the value is not there }