How to redirect to another page in controller

Question

I have developed one visualforce page and controller for account object and checking account.type is empty or not. If account.type is empty then page should be redirect to other page, this should be execute whenever page is reload or refresh. I called docheck method inside constructor but page is not redirecting to other page when account.type is empty.

Can anybody help me on this requirement

public class myaccountcontroller
{
  public String accId {get;set;}

  public myaccountcontroller(ApexPages.StandardController sc)
  {
    accId = ApexPages.CurrentPage().getparameters().get('id');
    doCheck();
  }

  public PageReference doCheck()
  {
     Account acc = [SELECT Id,Name,Type FROM Account WHERE Id=:accId];

     if(acc.Type =='')
     {
        PageReference mainHome= Page.Custom_Error_Page; 
        mainHome.setRedirect(true);
        return mainHome;
     }
  }
}

<apex:page standardcontroller="Account" extensions="myaccountcontroller">
-------------------
-------------------
-------------------
</apex:page>

Answer 1

While doCheck() is returning a redirect, it's doing so in the constructor. Since the constructor does not and cannot return a PageReference, the redirect is never actually reaching the page. You'll need to update your Visualforce page so that it it calls doCheck() through an action, which will then return the redirect to the page. Please see the following documentation on actions.

https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_compref_actionSupport.htm

On a side note, there's a good chance you're getting an SObject exception for accessing an un-queried field. You're checking if acc.Type == '', but you didn't include Type in your field list in you account query.