Guidelines for resizing (Windows Store apps)
These guidelines help ensure that your app looks great when Windows needs to resize it. Windows automatically resizes your app when the user changes the view state or calls up the soft keyboard.
Use the default behavior
To reduce the development effort on your part, you should let Windows handle the resize and reflow of content whenever possible.
Use custom handling
If the default behavior is inadequate, you can implement custom handling. For example, let's say you have an email app and you want to ensure a good user experience when Windows resizes the app when users are typing a new message with the soft keyboard. You can customize the resize the input field to take up the entire viewable area, allowing users to see the maximum amount of their message as they create it. Such behavior is not automatically performed by Windows.
Do NOT perform custom handling if the resulting layout is identical to what Windows would have provided.
Specify a minimum size for all input fields
Minimum sizes ensure that the input fields do not disappear when the windows are resized.
Test your application's resize behavior thoroughly
In particular, test that your app's input fields are not occluded by the soft keyboard.
Build date: 11/28/2012