My VisualForce Page Code

<apex:page standardController="Account_Plan__c" extensions="AccountPlanSort" tabStyle="Account" id="thePage">
    <apex:form id="theForm" >
        <!--Begin of Account Priority Block-->  
        <apex:pageBlock title="Sorting Account Priorities for {!Account_Plan__c.Name}" mode="edit" rendered="{!If(strType == 'AP', true, false)}">
                <apex:messages />
                    <apex:pageBlockButtons location="top">
                        <apex:commandButton value="Update" action="{!UpdateAction}"/>
                        <apex:commandButton value="Cancel" action="{!Cancel}"/>
                    </apex:pageBlockButtons>
                    <apex:pageBlockTable value="{!actPList}" var="item">
                        <apex:column headervalue="#">
                            <apex:inputField value="{!item.Field1__c}" style="width:25px"/>
                        </apex:column>
                        <apex:column value="{!item.Name}"/>
                    </apex:pageBlockTable>
            </apex:pageBlock>
        <!--End of Account Priority Block-->
        
    </apex:form>
</apex:page>

My APEX Code too

public with sharing class AccountPlanSort {    

    public ApexPages.StandardController stdController {get; set;}
    public Account_Plan__c AccountPlan {get; set;}
    public list<Company_Priorities__c> actPList  {get; set;}    //Account Priorities Sort
    public string strType {get; set;}

    public AccountPlanSort (ApexPages.StandardController stdController){
        System.debug('Is it in the Constructor');
        this.stdController = stdController;
        this.AccountPlan = (Account_Plan__c)this.stdController.getRecord();
        //actPList = [select Field1__c,Account_Priorities__c from Company_Priorities__c where Account_Plan__c =: AccountPlan.Id ORDER BY Field1__c ASC ];
        actPList = [select Field1__c, Name from Company_Priorities__c where Account_Plan__c =: AccountPlan.Id ORDER BY Field1__c ASC ];
        strType = ApexPages.currentPage().getParameters().get('type');
    }

    public PageReference UpdateAction(){
            set<Decimal> duplicate_Check = new set<Decimal>();
            Boolean IsDuplicateLis = false;
            Savepoint sp = Database.setSavepoint();
        try{
            if (strType=='AP'){
                List<Company_Priorities__c> actPList = [select Field1__c from Company_Priorities__c];
                for(Company_Priorities__c cp : actPList)
                {
                    if(duplicate_Check.contains(cp.Field1__c)==false)   //checking if the cuurent element is already present or not
                    duplicate_Check.add(Integer.valueOf(cp.Field1__c));
                    else {
                            IsDuplicateLis =true;
                         }
                }
                    if(IsDuplicateLis ==false){
                            update actPList;
                    }else{
                            ApexPages.Message msg = new ApexPages.Message(Apexpages.Severity.ERROR, 'This sorting number already exists');              
                            ApexPages.addMessage(msg);
}
            }
catch(Exception e){
            System.debug('H'+e.getMessage());
            Database.rollback(sp);
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR,e.getMessage()));
        }
        return new PageReference('/'+AccountPlan.id);
    }
}