I have a visualforce page for a custom object which has the account object as its master detail relationship. I want to override the new button on the custom object with the visualforce page, so I have made the custom object the standard controller. 
I need the account master detail field to autopopulate to the account which the user has clicked new from. i.e. if the user is on Account A and clicks "New Account Property" Account A should be pre-populated in the account field on the visualforce page.
I believe someone had a similar problem which was resolved in https://developer.salesforce.com/forums/?id=906F000000094yMIAQ, however this doesn't seem to work for me. 

VisualForce page
 

<apex:page StandardController="Account_Property__c" extensions="accountProperty" sidebar="false" lightningStylesheets="true">
    <apex:sectionHeader title="Edit AccountProperty" />
    <apex:form >
        <apex:messages />    
        <apex:pageBlock title="Edit AccountProperty" id="thePageBlock" mode="edit">
            <apex:pageMessages />
            <apex:pageBlockButtons >
                <apex:commandButton value="Save" action="{!SaveBoth}"/>
                <apex:commandButton value="Cancel" action="{!cancel}"/>
            </apex:pageBlockButtons>
            <apex:actionRegion >
                <apex:pageBlockSection title="Property Information" columns="1">
                    
                    <apex:pageBlockSectionItem >   
                        
                        <apex:outputLabel value="Property_Name__c"/>
                        <apex:outputPanel >                            
                            <apex:inputField value="{!objB.Property_Name__c}">
                                <apex:actionSupport event="onchange" rerender="thePageBlock"
                                                    status="status"/>
                            </apex:inputField>
                            <apex:actionStatus startText="applying value..." id="status"/>
                        </apex:outputPanel>
                    </apex:pageBlockSectionItem>
                </apex:pageBlockSection>
            </apex:actionRegion>
            <apex:pageBlockSection title="Sunrise ID" columns="1"
                                   rendered="{!objB.Property_Name__c == 'SPI_ID'}">
                
                <apex:inputField value="{!objB.Account__c}" />
                <apex:inputField value="{!objB.SPI_ID__c}" required="true"/>
                <apex:inputField value="{!objB.Start_Date__c}" required="true"/>
                <apex:inputField value="{!objB.Implementation_Date__c}" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockSection title="SVU Site ID" columns="1"
                                   rendered="{!objB.Property_Name__c == 'SLI_ID'}">
                
                <apex:inputField value="{!objB.Account__c}" />
                <apex:inputField value="{!objB.SLI_ID__c}" required="true"/>
                <apex:inputField value="{!objB.Start_Date__c}" required="true"/>
                <apex:inputField value="{!objB.Implementation_Date__c}" required="true"/>
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>

Controller
 

public with sharing class accountProperty {
    
    ApexPages.StandardController sc;
    public Account_Property__c objB {get; set;}
    public Account objA {get;set;}
    
   
    private final Account_Property__c detail;
    private final Account master;
    private final Map<String, String> currentpageParams;
    
    public accountProperty(ApexPages.StandardController sc)
    {

        
        this.sc = sc;

        this.detail = (Account_Property__c)sc.getRecord();
        master = [select id from Account where id = :ApexPages.currentPage().getParameters().get(detail.id + '_lkid')];
        if(detail.Account__c==null){
            detail.Account__c = master.Id;
        }
        
        
        //this.currentpageParams = ApexPages.currentPage().getParameters();
        
        //Set<String> mapKeySet = this.currentpageParams.keySet();
        //for (String g : mapKeySet)
        //{
            //if (g.endsWith('_id'))
            //{
                //master = [select id from Account where id = :ApexPages.currentPage().getParameters().get(detail.id + '_lkid')];
            	
                //this.detail.Account__c = master.Id;
                //break;
                //system.debug(g);
            //}
        //}
        
        
        objB = new Account_Property__c();
    	//objB.Account__c = objA.Id;
        //Account acc = (Account) sc.getRecord();
        //objB.Account__c = sc.getId();
        objB.Implementation_Date__c = system.TODAY()+1;
        //acc.Name = objB.AccountName__c;
    }
    
    public ApexPages.PageReference SaveBoth()
    { try
    	{
        insert objB;
        	PageReference successPage = Page.AccountPropertySaved;
            successPage.setRedirect(true);
            successPage.getParameters().put('id',sc.getId());
            return successPage;

        }
     catch(DMLException e) {
         ApexPages.addMessages(e);
     }
     return null;
        
    }

}