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
      });     //var dirlist=[];
          
      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))dirlist.push(ths);
                  
          if  (app.IsFolder(pth))            self.lstFolds.AddItem(ths, null, "folder")      
        }      
        ths  =  lst.shift();    
      }        // self.lstFolds.SetList(dirlist.join(","));
          
      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()