This is a simple dialog to allow a user to choose a file folder.

See also Sample File Picker

folderpicker.js

//Called when application is started
function OnStart(){
    //Create a layout with objects vertically centered.
    lay = app.CreateLayout( "linear", "Vertical,FillXY" );    
 
    //Create a text label and add it to layout.
    btn = app.CreateButton( "FolderPicker demo" );
    lay.AddChild( btn );
    btn.SetOnTouch(btn_OnTouch);
    
    //Add layout to app.    
    app.AddLayout( lay );
    pick = new FolderPicker(mycallback);
    // don't show hidden files
    pick.SetHideFiles(true);
}//function Onstart()
 
 
function btn_OnTouch(){
    pick.SetFolder("/sdcard");
    pick.Show();    
}//function btn_OnTouch()
 
function mycallback(fullpath){
  app.Alert("user chose " + fullpath)
}//function mycallback()
 
function FolderPicker(Callback,basePath){
  var self = this;
  this.basePath = basePath || "/sdcard";
  this.callback = Callback || function(){};
  this.FolderPath = this.basePath;
  this.hideHiddenFiles = false;
  this.dlg = app.CreateDialog(this.basePath);
  this.lay = app.CreateLayout( "linear", "horizontal,fillxy" );
  
  this.lstFolds = app.CreateList("blank" , 0.7, 0.7 );
  this.lstFolds.parent = self;
  this.lstFolds.SetOnTouch(FolderPicker_NewFolder);  
  this.lay.AddChild(this.lstFolds);
 
  var vlay = app.CreateLayout( "linear", "vertical,fillxy" );
  this.okBtn = app.CreateButton("Ok");
  this.okBtn.parent = self;
  this.okBtn.SetOnTouch(FolderPicker_Select);
  vlay.AddChild(this.okBtn);  
  this.cancelBtn = app.CreateButton("Cancel");
  this.cancelBtn.parent = self;
  this.cancelBtn.SetOnTouch(FolderPicker_Select);
  vlay.AddChild(this.cancelBtn);  
 
  this.lay.AddChild(vlay)
 
  this.dlg.AddLayout(this.lay);
 
  this.Show = function(){
    self.dlg.Show();
  }
  this.SetHideFiles=function(val){
    if(val == undefined) val = true;
    self.hideHiddenFiles = val;
  }
  this.Hide = function(){
    self.dlg.Hide();
  }
  this.GetFolder = function(){
    return self.FolderPath;
  }
  this.SetFolder = function(folderPath){
    self.FolderPath = folderPath;
    self.dlg.SetTitle(folderPath);
    app.ShowProgress( "Loading..." );
    var lst = app.ListFolder(folderPath);
    lst.sort(function(x,y){return (x.toLowerCase() > y.toLowerCase())?1:-1});
    self.lstFolds.SetList("");
    if( self.FolderPath != self.basePath )
      self.lstFolds.AddItem("..",null,"folder");
    var ths = lst.shift();
    while (undefined != ths) {
      if ((! self.hideHiddenFiles) || (ths.indexOf(".") != 0)){
        var pth = folderPath + "/" + ths;
        if (app.IsFolder(pth))
           self.lstFolds.AddItem(ths,null,"folder")
      }
      ths = lst.shift();
    }
    
    app.HideProgress();
  }  
}//function FolderPicker()
 
function FolderPicker_NewFolder(fil){
  var par = this.parent;
  var pth = par.GetFolder();
  if (fil != "..") {
      pth += "/" + fil
  }
  else{
     if( pth == par.basePath || pth == "/" ){
       par.Hide()
       return;
     }
     var tst = pth.split("/");
     tmp = tst.pop();
     pth = (tst.join("/"));
  }  
  par.SetFolder(pth);
}//function FolderPicker_NewFolder()
 
function FolderPicker_Select(fil){
  var par = this.parent;
  var pth = par.GetFolder();
  par.Hide();
  if(this.GetText() == "Ok") par.callback(pth );
}//function FolderPicker_Select()