Hi

  Try to use this... 

I have designed two pages one inline visualforce page named "OveriddingPriceBook2buttom" another  is "TestOnOpportunity"

which is ovridden with view button.. This is my code you can follow 

In line visualforce page and controller 
<apex:page standardController="Opportunity" extensions="PriceBookDemoController" >
     {!OppName}
     <apex:sectionHeader title="Price Book" subtitle="{!OppName}"/>
       <apex:form >
         <apex:pageBlock title="Choose Price Book for:">
          <apex:pageBlockButtons location="bottom">
              <apex:commandButton value="Save" action="{!save}"/>
              <apex:commandButton value="Cancel" action="{!cancel}"/>
          </apex:pageBlockButtons>
         <apex:panelGrid columns="3">
             <apex:outputText value=" Price Book"/>&nbsp;
                 <apex:selectList id="status2" size="1" multiselect="false" >
            <apex:selectOptions value="{!SelectBranchOptions}"/>
        </apex:selectList>
       </apex:panelGrid>
  </apex:pageBlock>
    </apex:form>
</apex:page>

My controller is 
public class PriceBookDemoController {
public String OppName{set;get;}
Id OpportunityId;
    public PriceBookDemoController(ApexPages.StandardController controller) {
      OpportunityId = apexPages.currentPage().getParameters().get('id');
      Opportunity Opp = [select Id,Name from Opportunity where id =: OpportunityId];
      OppName = Opp.Name;
    }
     
  public List<SelectOption> getSelectBranchOptions() {
  List<SelectOption> options = new List<SelectOption>();
  for(pricebook2 pb:[select id,name from pricebook2 where isactive = true]) {
    options.add(new SelectOption(pb.id,pb.name));
  }
  return options;
}
}

 My page which is overidden with view button is..

<apex:page standardcontroller="Opportunity">
    
        <apex:detail  relatedlist="true" inlineedit="true" >
        
        
    
            <apex:include pageName="OveriddingPriceBook2buttom" rendered="false"/>
         </apex:detail >
</apex:page>

 DId this post answers your questions if so please mark it solved so that others get benifited 

Thanks