Multi selection allowed failing in object describe

Question

My code fails for multiselection of describe object iam getting following error.

System.NullPointerException: Attempt to de-reference a null object Error is in expression '{!showFields}' in component in page describ: Class.APU001_Describe.showFields: line 53, column 1

Class.APU001_Describe.showFields: line 53, column 1

Below is my code VF page code

<apex:page controller="APU001_Describe"   contentType="{!renderAsExcel}" sidebar="false">

<style>
  fieldset.scheduler-border {
    border: 1px groove #ddd !important;
    padding: 0 1.4em 1.4em 1.4em !important;
    margin: 0 0 1.5em 0 !important;
    -webkit-box-shadow:  0px 0px 0px 0px #000;
    box-shadow:  0px 0px 0px 0px #000;
    margin-left:8% !important;
    width:63%;
}

    legend.scheduler-border {
        font-size: 1.2em !important;
        font-weight: bold !important;
        text-align: left !important;
        width:auto;
        padding:0 10px;
        border-bottom:none;
    }
    .bodyDiv{
 height:400px;
}
.Btn-group{
  width:60% !important;
}
.frm{
  margin:15px;
}
.modal {
    outline:none;
}
</style>  
<apex:form id="Describe">


 <apex:pageBlock id="block2" >
<apex:pageblockbuttons location="top" >
<apex:commandButton value="Fetch Object Fields"  rerender="Describe" action="{!showFields}"/>

</apex:pageblockbuttons>
<apex:pageblocksection >

<apex:selectList value="{!selectedObject}" multiselect="True" size="3">


<apex:selectOptions value="{!objectNames}" />



</apex:selectList>

</apex:pageblocksection>


 <apex:pageBlockTable value="{!fields}" var="fls">  
    <style>
body
{
   background-color: blue; } 
 <apex:column value="{!fls.key}" headerValue="Field Name"/> 
 <apex:column value="{!fls.fieldAPIName }" headerValue="Field API Name"/>    
 <apex:column value="{!fls.val}" headerValue="Field Type"/> 
          </style>

</apex:pageBlockTable>


<apex:pageblocksection id="fieldList" rendered="{!not(isnull(selectedObject))}">




     <!--Apex:commandButton value="Export to Excel" action="{!SaveAsCSV}" /-->
    <Apex:commandButton value="Export to Excel" onclick="return window.open('/apex/Describ?core.apexpages.devmode.url=1)"/>


</apex:pageblocksection>
</apex:pageBlock>
</apex:form>
 </apex:page>

Below is my controller code

public class APU001_Describe
{
public Map <String, Schema.SObjectType> schemaMap = Schema.getGlobalDescribe();
public List<Pair> lstfieldname{get;set;}
public List <Pair> fields {get{return lstfieldname;} set{lstfieldname =value;}}
public List <SelectOption> objectNames{public get; private set;}
public List<SelectOption> fieldNames {public get; private set;}   
public String selectedFields {get; set;}    
public String selectedObject {get; set;}
public string header{get;set;}
public string renderAsExcel{get;set;}


// Intialize objectNames and fields

public APU001_Describe() {
objectNames = initObjNames();
fields = new List<Pair>();

header ='lstfieldname,fields,objectName\r\n';
}
// Populate SelectOption list -

// find all sObjects available in the organization

private List<SelectOption> initObjNames() {
List<SelectOption> objNames = new List<SelectOption>();
 List<SelectOption> fieldNames = new List<SelectOption>();
List<String> entities = new List<String>(schemaMap.keySet());
entities.sort();
for(String name : entities)
objNames.add(new SelectOption(name,name));
return objNames;

}




 // public PageReference SaveAspdf() {      
        //renderAsdoc='pdf';
        //setup a default file name
       // string fileName = 'DataList '+date.today()+'.pdf';
       // Apexpages.currentPage().getHeaders().put('content-disposition', 'attachemnt; filename='+fileName);      
      //  return null;
   // }

// Find the fields for the selected object

public  void showFields() {
fields.clear();

Map <String, Schema.SObjectField> fieldMap = schemaMap.get(selectedObject).getDescribe().fields.getMap();




for(Schema.SObjectField sfield : fieldMap.Values())
{
schema.describefieldresult dfield = sfield.getDescribe();
//system.debug('#######' + dfield );
Pair field = new Pair();
field.key = dfield.getLabel();
//system.debug('#######4444' + field.key);
field.val = dfield.getType () + ' : ' + dfield.getLabel ();
field.fieldAPIName = dfield.getname();

//field.formulafield =dfield.calculatedformula();
//field.Length = dfield.getLength();
lstfieldname.add(field);
//renderAsExcel='application/vnd.ms-excel#Data Report.csv';
}
    for(Schema.SObjectField sfield : fieldMap.Values()){
    schema.describefieldresult dfield = sfield.getDescribe();
    fieldNames.add(new SelectOption(dfield.getName(),dfield.getLabel()));
}
}

 public PageReference SaveAsCSV() {
        renderAsExcel='application/vnd.ms-excel#Data Report.xls';
   return null;
 }
public class Pair
{
public String key {get; set;}
public String val {get; set;}
public String fieldAPIName{get;set;}
//public String Length{get;set;}
 //public String formulafield{get;set}
}
}

Answer 1

Since it's a multi-select, but you're putting it in to a string, you'll end up trying to get values that don't exist in the field map. Instead, you'd want to use a list, and if there are any selected values, then use those.

Here's the minimum changes you'd need to make:

public String[] selectedObject {get; set;}

...

public  void showFields() {
    fields.clear(); 
    if(selectedObject != null) {
        for(String obj: selectedObject) {
            Map <String, Schema.SObjectField> fieldMap = schemaMap.get(obj).getDescribe().fields.getMap();
            for(Schema.SObjectField sfield : fieldMap.Values())
            {
                schema.describefieldresult dfield = sfield.getDescribe();
                //system.debug('#######' + dfield );
                Pair field = new Pair();
                field.key = dfield.getLabel();
                //system.debug('#######4444' + field.key);
                field.val = dfield.getType () + ' : ' + dfield.getLabel ();
                field.fieldAPIName = dfield.getname();

                //field.formulafield =dfield.calculatedformula();
                //field.Length = dfield.getLength();
                lstfieldname.add(field);
                //renderAsExcel='application/vnd.ms-excel#Data Report.csv';
            }
            for(Schema.SObjectField sfield : fieldMap.Values()){
                schema.describefieldresult dfield = sfield.getDescribe();
                fieldNames.add(new SelectOption(dfield.getName(),dfield.getLabel()));
            }
        }
    }
}

Feel free to rename the variables, etc, as necessary.

---

The fieldNames variable needs to be initialized. The initObjNames method initializes a local variable by the same name, but that's not the same variable as in the class.

public APU001_Describe() {
    objectNames = initObjNames();
    fields = new List<Pair>();
    fieldNames = new List<SelectOption>();
    header ='lstfieldname,fields,objectName\r\n';
}

Which you should probably clear() before starting anew in the showFields function:

public void showFields() {
    fieldNames.clear();
    // rest of code from above