populate a combobox based on previous combobox selection in XML

Question

I am a .net beginner. I am reading a XML file and showing it in two comboboxes ie., cbProduct and cbBrandName

I need to show text in cbBr

Answer 1

LINQ looks much more scary than it is. There's two bits of it being used in Anirudha's answer, which I'll try to explain. The first is .Select(x=>. This means "For each thing in the list, replace it with something". The x represents each item in the list.

For example:

new string[]{"a", "b", "c"}.Select(x=>x.ToUpper()); 

turns an array of {"a", "b", "c"}, into an array of {"A", "B", "C"}. It's just saying "Take the each thing in the list, and replace it with whatever you get by calling ToUpper() on it.

The other bit of LINQ is .Where(x=>. That just says "Give me a smaller list which only has things where this statement is true". So

new string[]{"a", "b", "c"}.Where(x=>x == "a"); 

will give you a list of {"a"}. Replacing x == "a" with x != "b" will give you a list of {"a", "c"}. So in the second bit of code, you're saying "before I do that thing where I replace each item with its productname, I want to filter out anything that doesn't match what I want to match. Then I transform what's left."

---

To apply these to the code example, I'll reformat the lines and comment them.

// To set the first combo box:
cbProduct.Items.AddRange( // Add everything we produce from this to the cbProduct list
    doc.Descendants("items") // For each thing that represents an "items" tag and it's subtags
    .Select(x=>x.Element("productname").Value) // Transform it by getting the "productname" element and reading it's Value.
    .ToArray<string>()); // Then convert that into a string[].


// To set the second combo box:
string product2Search=cbProduct.SelectedItem.ToString();// get the currently selected value of cbProduct.
cbBrandName.Items.Clear(); //clears all items in cbBrandNamedoc
cbBrandName.Items.AddRange( // Add everything we produce from this to the cbBrandName list
  doc.Descendants("items") // For each thing that represents an "items" tag and it's subtags
  .Where(x=>x.Element("productname").Value==product2Search) // Filter our list to only those things where the productname matches what's currently selected in cbProduct (which we just stored)
  .Select(y=>y.Element("brandname").Value) // Transform it by getting the "brandname" element and reading it's Value.
  .ToArray<string>()); // Then convert that into a string[]

Is that helpful? When I'm coding myself, I like to split long LINQ statements up by putting them on separate lines like this, and then I can just read down the lines: "I get a list WHERE this is true, then SELECT this other thing based on it, and turn it into an ARRAY."

Answer 2

In LINQ2XML

XElement doc=XElement.Load(@"..\..\stock.xml");

//put this code in the form_load event
cbProduct.Items.AddRange(doc.Descendants("items").Select(x=>x.Element("productname").Value).ToArray<string>());//adds all products

//put this code in the SelectedIndexChanged event of cbProduct
string product2Search=cbProduct.SelectedItem.ToString();//selected value of cbProduct
cbBrandNamedoc.Items.Clear(); //clears all items in cbBrandNamedoc
cbBrandNamedoc.Items.AddRange(doc.Descendants("items").Where(x=>x.Element("productname").Value==product2Search).Select(y=>y.Element("brandname").Value).ToArray<string>());