mapPanel topToolbar functions doesn't works

[tah_206207]

I use geoExt with ExtJs3.4 in my application!.I create a mapPanel and add openlayers map into it with below code.

var mapPanel = new GeoExt.MapPanel({
        renderTo: 'gxmap',
        height: 500,
        width: 800,
        map: map,
        title: 'Map'
    });

after that i create extjs toggle button

var button = new Ext.Button({
text: 'Measure Things',
enableToggle: true,
handler: function(toggled){
    if (toggled) {
        polygon.activate();
    } else {
        polygon.deactivate();
    }
}
});

when i want to add this button to map panel i get topPanel of mapPanel and after that when i want to use topPanel functions these functions doesn't works!

mapPanel.getTopToolbar().addButton(button);

or below code

topToolbar = mapPanel.getTopToolbar();
topToolbar.addButton(button);

when i see chrome developer tool i see this error for addButton function or other functions of topToolbar of panel! error:

uncaught typeError: cannot call method 'addButton' of undefined

why i can't use topToolbar functions?
Link for tutorial of geoext that use mapPanel.getTToolbar().addButton(button);
http://geoext.org/tutorials/control-...#extjs-buttons

[sword-it]

when i want to add this button to map panel i get topPanel of mapPanel and after that when i want to use topPanel functions these functions doesn't works!
mapPanel.getTToolbar().addButton(button);
or below code
topToolbar = mapPanel.getTToolbar();

HI!
i guess, you are using wrong code to get toptoolbar
it must be,

mapPanel.getTopToolbar().addButton(button);

[tah_206207]

Excuse me! this is type error
i use mapPanel.getTopToolbar().addButton(button); but when i want to use getTopToolbar() functions doesn't work!
chrome shows Error for getTopToolbar() functions!