Refresh Listview data based on Selection of a Dropdown

Question

Hello I am using aSP.net 4.5 Web Forms. I have a listview whose SelectMethod is set. In the header of ListView I have a dropdown whose data is populated dynamically & set Datasource. Now based on the selection of drop down I want to show items in ListView. I am not able to get this part. Here's my code : DataKeyNames=ChannelId ItemType=VincitoreCRMApplication.Models.ChannelViewModel SelectMethod=GetData >   In the code behind : protected void Page_Load(object sender EventArgs e) { if (!IsPostBack) { // Populate DropDown Countries DropDownList CountryList = ListView1.FindControl(CountryList) as DropDownList; if (CountryList != null) { CountryList.DataSource = GetCountries(); CountryList.DataBind(); CountryList.SelectedIndex = -1; } } } // Model binding method to get List of Channel entries // USAGE: public IQueryable GetData() { return _db.Channels .Select(u => new ChannelViewModel { ChannelId = u.ChannelId NameSuffix = u.NameSuffix FirstName = u.FirstName LastName = u.LastName City = u.City State = u.State Country = u.Country }); //return _db.Channels; } public string[] GetCountries() { List list = GetData().Select(o => o.Country).Distinct().ToList (); list.Insert(0 --- Filter ---); list.RemoveAll(s => s == null); return list.ToArray(); } // Selection Event of CountryList DropDown protected void CountryList_SelectedIndexChanged(object sender EventArgs e) { DropDownList CountryList = ListView1.FindControl(CountryList) as DropDownList; if (CountryList != null) { System.Diagnostics.Debug.WriteLine(Selected Index =  + CountryList.SelectedIndex); if (CountryList.SelectedIndex > -1) // This also gives proepr result System.Diagnostics.Debug.WriteLine(Selected text =  + CountryList.Text); } } Now the only part I am stuck is how do I refresh the GetData() using the selected Country from drop down. If I set a parameter in GetData then how do I pass parameter in SelectMethod part. I believe I can set the DataSource and Databind of ListView programmatically & get it work. But I think using Model Binding is more worth than using DataSource/Databind pattern. Also I wont be adding/Editing/Deleting items in the Lsitview - it is just for display & viewing with a facility to filter the data based on selection. Can anyone please suggest me for the above. I am not able to get any expected result from googling the same. Kindly try to help me at the earliest. Thanks

Terry · Answer

Hello Friends Sharing the solution to my question. With the reference to link shared by Vincent I found that in all the examples shown the drop down was out on ListView/GridView. The site says that parameter to SelectMethod can be pass of type Control Query string Value etc. With string as value of dropdown none of them worked for me. So I came up to : Added dropdown out of ListView. And set it's DataValue DataText fields and SelectMethod and setting an object for it. Here important part was the DataValueField should be of int. I have tried with Enum and that also works. Here is my code for the dropdown : AppendDataBoundItems=true ItemType=VincitoreCRMApplication.Models.ChannelViewModel DataValueField=ID DataTextField=Country SelectMethod=GetCountryList > Code-BEHIND // GET COUNTRY LIST FOR DROP DOWN public IEnumerable GetCountryList() { var countryList = _db.Channels.Where(o => !o.Country.Equals(string.Empty)) .Select(o => o.Country).Distinct().ToList(); int id = 1; List list = new List (); foreach (var country in countryList) { if (country != null) { ChannelViewModel c = new ChannelViewModel(); c.ID = id++; c.Country = country; list.Add(c); } } return list; } Check the ID (DataValueField) and the created ID property in the Model. This was the key to work on this. Then in my GetData() i.e. the SelectMethod of ListView I added [Control]int? parameter : // Model binding method to get Grid of Channel entries // USAGE: public IQueryable GetData([System.Web.ModelBinding.Control]int? countryList) { IQueryable cvm = _db.Channels .Select(u => new ChannelViewModel { ChannelId = u.ChannelId NameSuffix = u.NameSuffix FirstName = u.FirstName LastName = u.LastName City = u.City State = u.State Country = u.Country }); if (countryList > 0) { System.Diagnostics.Debug.WriteLine(Value =  + CountryList.SelectedValue); cvm = cvm.Where(c => c.Country == CountryList.SelectedItem.Text); } return cvm; } And I could filter the list of data based on the selection of dropdown. It works like a charm. NOTE: The parameter passed to GetData() can't be of type string? because initially string value will be null and that isn't accepted in any ways. But it works well with int? or ? . I haven't tried with any other object/Model so don't know about it. But the KEY is to create a seperate Model or add another Property in the Model and make that as the DataValueField for the DropDownList and we are done with the ModelBinding. Hope this could help someone. Thanks to everyone for supporting me and suggesting me the needful. Vincent special thanks to you.

Vincent Maverick Durano · Answer

Again my replies may not actually gives you full solution but I think I somehow helped you to move forward. Regarding your last question. I'm not sure if that would be possible at the moment to mark your own reply as answer. Having said that just please do post your full solution for future reference. Thanks.

Terry · Answer

Well Vincent Your code works but it doesn't eliminate the value's with null. So an item with null value is also added in the countrylist. I added if (country != null) and things works fine. Thanks for this Linq statement. Thanks once again.

Vincent Maverick Durano · Answer

Not tested on this but could please try something like: var countryList = _db.Channels.Where(o => !o.Country.Equals(string.Empty)) .Select(o => o.Country).Distinct().ToList(); int id = 1; List list = new List (); foreach (var country in countryList){ list.Add(new ChannelViewModel { ID = id++  Country = country}); } return list;

Terry · Answer

From that site I just found that in all examples the dropdown control is out of the ListView or GridView only & not in the ItemTemplate - which I was more interested for. Secondly all examples passes int? only. Looking at that I tried my way implementing with int? by creating an object and adding an ID in it & setting that ID as DataValueField for the drop down. Then also tried with Enum that also worked. But string? didn't work in any ways. Though the site mentions Query string Value but I couldn't make it happen. Anyways Thanks a lot for your response. In this can you suggest a better option : // GET COUNTRY LIST FOR DROP DOWN public IEnumerable GetCountryList() { IEnumerable cvm = _db.Channels .Select(u => new ChannelViewModel { ChannelId = u.ChannelId Country = u.Country }).ToList (); //.ToList (); List cvm1 = cvm.Select(o => o.Country).Distinct().ToList (); cvm1.RemoveAll(s => s == null); cvm1.RemoveAll(s => s == String.Empty); int id = 1; List list = new List (); foreach (String s in cvm1) { ChannelViewModel c = new ChannelViewModel(); c.ID = id++; c.Country = s; list.Add(c); } return list; } I want list of unique Country's from the collection of data. In my above code you can see how much I am doing to achieve the goal. I hope their should be some easier & straight forward method that I am missing out. Can you suggest for the above. Thanks.

Terry · Answer

Thanks Vincent I had a look at that site. That says we can send parameters any of such examples : Controls on the page Query string values View data Session state Cookies Posted form data View state Custom value providers are supported as well This site didn't solved my issue what I was looking for. But I learned something my way by asking the same question in other sites & more research. In my case Control wasn't working because it was passing string value & nor string? was working as string can be null and the parameter cannot accept null. From this site I couldn't get why my string? wasn't working. But finally got that it needs either int Enum - basically whatever Value passed is int. Don't know if any other object also works !!. And this Filtering dropdown what I had in that doesn't work. I got to have it outside the ListView & then bind the dropdown with the SelectMethod passing the parameter value of the dropdown item. Thanks.

Vincent Maverick Durano · Answer

Well you can actually do like this to eliminate null values too: var countryList = _db.Channels.Where(o => !o.Country.Equals(string.Empty) && o.Country != null) .Select(o => o.Country).Distinct().ToList();

Terry · Answer

Vincent As your reply didn't give me solution for my question and I somehow figured out and shared my answer/solution for my question. Is their a way that I can mark my reply as Answer so can close this thread and others can also refer the same and find the solution.

Vincent Maverick Durano · Answer

Hi Terry The link that i've posted is just a reference on how to pass parameters using model bindings. I can't provide you actual code as I didn't use ModelBindings yet but I was hoping that could give you a good start on resolving your issue.

Vincent Maverick Durano · Answer

Take a look at Value Providers in Model Binding section in this post: https://msdn.microsoft.com/en-us/vs11trainingcourse_aspnetwebforms45_topic2.aspx