Unable to use setTitle method when using a string concatenated with datastore data

I have the following code attached as a handler to a button:

myapp.stores.vehicleInfo.load();
myapp.toolbars.vehicleInfoToolbar.setTitle('Image 1 of ');

Which within my defined namespace loads the store and then sets the title of a toolbar - this works.

This code doesn't work:

myapp.stores.vehicleInfo.load();
myapp.toolbars.vehicleInfoToolbar.setTitle('Image 1 of' + myapp.stores.vehicleInfo.data.items[0].data.imageTotal);

giv开发者_如何学编程ing the error: 'cannot read property of "data" of undefined'

But when I click the button a second time, it sets the title of the toolbar as expected e.g. Image 1 of 10.

What is going on here? How do I solve this? I tried using the settimeout method in case the setTitle method was being called too early before the store was finished loading. However this failed to solve the problem.

Thanks.

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the store load() method is asynchronous and it usualy takes a while to load the store so ... you should set the title on the callback function when you are certain you have the data

myapp.stores.vehicleInfo.load({
                callback:function(r, options, success) {
                    myapp.toolbars.vehicleInfoToolbar.setTitle('Image 1 of' + myapp.stores.vehicleInfo.data.items[0].data.imageTotal);
                }
            });

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The store is not loaded yet when the setTitle is called. You should put call to setTitle into load's callback:

myapp.stores.vehicleInfo.load({callback : function(records){
  myapp.toolbars.vehicleInfoToolbar.setTitle('Image 1 of' + records[0].data.imageTotal);
}});