Ui Update Path Dynamically

Hello , i'm trying to make an UI to import my presets .ffx

I have a main folder named MyPresetFolder ,and inside ,two other folders named Preset_Files_01 and Preset_Files_02 .

and inside each Presets_Files ,a lot of .ffx

What i want to do with my ui is when i choose the file 1 or 2 ,the seconde line update the list to load ...

with my code, it's works only at the beginning ..i dont know how to said if i change the select folder,update the folder preset.....

if someboy can help me ??

Thanks everyone...

Here is my code

function FFX(obj)

//===============================================

    //================= UI============================

    //===============================================

{   

    function addHGroup(conteneur){

var groupe = conteneur.add("group");

groupe.alignChildren = ["fill","fill"];

groupe.orientation = "row";

groupe.spacing = 1;

groupe.margins = 0;

return groupe;

    }

    function addVGroup(conteneur){

        var groupe = conteneur.add("group");

        groupe.alignChildren = ["fill","fill"];

        groupe.orientation = "column";

        groupe.spacing = 1;

        groupe.margins = 0;

        return groupe;

    }   

    var fenetre = obj instanceof Panel ? obj : new Window("window","MyPresets",undefined,{resizeable:true});

    fenetre.alignChildren = ["fill", "top"];

    fenetre.spacing  = 2;

    fenetre.margins = 3;

    var versionGroup3 = addHGroup(fenetre);

    versionGroup3.alignment = ["fill","bottom"];

    var widthGroup = addHGroup(fenetre);

    widthGroup.alignChildren = ["fill","center"];

    var PATH_Button = widthGroup.add("button",undefined,"Load");  

//________________________________________________________________________________________ ________________________________________________

  var presetsFolder = Folder("~/Desktop/MyPresetFolder");

var arrayPresets = presetsFolder.getFiles('Preset*'); 

var fileNames = getFileNames(arrayPresets); 

function getFileNames(arrayPresets) { 

    var fileNames = [], 

        baseName = ""; 

    for (var i = 0, il = arrayPresets.length; i < il; i++) { 

        baseName = arrayPresets[i].displayName.split("_")[0]; 

        fileNames.push(baseName); 

    } 

    return fileNames; 

} 

var widthGroup = addHGroup(fenetre);

widthGroup.add("statictext", [0,0,80,18], "Select Folder:");

var Chemin1 = widthGroup.add('dropdownlist', [0,0,200,18], fileNames);

            Chemin1.selection = 0;

            //alert(Chemin1.selection.text)

//________________________________________________________________________________________ ________________________________________________

  var presetsFolder2 = Folder("~/Desktop/MyPresetFolder/"+(Chemin1.selection.text));

    //alert(presetsFolder2)

var arrayPresets2 = presetsFolder2.getFiles('*.ffx'); 

var fileNames2 = getFileNames(arrayPresets2); 

function getFileNames(arrayPresets2) { 

    var fileNames2 = [], 

        baseName2 = ""; 

    for (var i = 0, il = arrayPresets2.length; i < il; i++) { 

        baseName2 = arrayPresets2[i].displayName.split(".")[0]; 

        fileNames2.push(baseName2); 

    } 

    return fileNames2; 

} 

var widthGroup = addHGroup(fenetre);

widthGroup.add("statictext", [0,0,80,18], "Select Preset:");

var Chemin2 = widthGroup.add('dropdownlist', [0,0,200,18], fileNames2);

            Chemin2.selection = 0;

//CLICK ALL____________________________________________________________________

PATH_Button.onClick = function (){

    }

//================= AFFICHAGE DE L'UI ============

    fenetre.layout.layout(true);

    fenetre.layout.resize();

    fenetre.onResizing = fenetre.onResize = function () {fenetre.layout.resize()};

    if (fenetre != null ) if (fenetre instanceof Window) fenetre.show();

    }

FFX(this);