how to get value from drop down to the controller using apex SelectOption?

Question

Controller Code -

public class ApplicationController {

    public String selectedApplicationId {get;set;}
    public static List<SelectOption> applicationOptions {
    get {
        if(applicationOptions == null) {
            applicationOptions = new List<SelectOption>(); 
            applicationOptions.add(new SelectOption('', 'None'));
        }
        return applicationOptions;
    } set;
}

    public static List<Application__c> apps{
    get {
        if (apps == null) {
            apps = new List<Application__c>();
        }
        return apps;
    }
    set;
}

public ApplicationController() {
    //basically get the contact ID from parameter
    contactID = parameters.get(CONTACT_ID);
     apps = [Select t.Id, t.Type__c, t.Name From Application__c t where t.contactID =: contactID];

        for(Application__c app : apps) {
            applicationOptions.add(new SelectOption(app.Id, app.Type__c + ' - ' + app.Name));
        }
}

public PageReference goToAnotherPage() {
//do something with the selected application ID
}

}

So on my page I have a button which I hit to get the selected application ID. But every time I hit the button it says

"applicationOptions: Validation Error: Value is not valid"

and the drop down is re-rendered with just None as its only value.

Can someone please guide me where am I going wrong? All the examples that I have seen have options being created as part of the getter/setter but I need to dynamically populate the application options.

Answer 1

It seems like you have not initialized applicationOptions list in your constructor where you are adding values to select options, try initializing as

applicationOptions = new List<SelectOption>();  

Answer 2

I resolved this. Remove the static from applicationOptions and moved the lines from controller to populate the applicationOptions into the getter itself.

Answer 3

Here is my implementation. Controller

public string countryId {get;set;}

public void Submit(){
//countryId will have the required value
}

public List<SelectOption> getCountries()
{
    List<selectOption> options = new List<selectOption>();
    try
    {
        for (Country__c c : [SELECT id, Name FROM Country__c])
        {
            options.add(new selectOption(c.id, c.Name));
        }
    }
    catch(Exception e)
    {
        ApexPages.addMessages(e);
    }       
    return options;
}

Visualforce Page

    <apex:form>
   <apex:selectList title="Select Country *" tabindex="11" id="ddlCountry" value="{!countryId}"  styleClass="ddlCountry required fs-18 color-blue3 fw-200 lh-22 ddlCombo" size="1" >
<ap</apex:selectList>
    <apex:commandButton immediate="false"  id="btnSubmit" styleClass="" value="Submit"  action="{!Submit}" />  
    </apex:form>

I have extracted above from my working page please ask if you have any difficulty implementing this.