问题
In the documentation for the FileSavePicker, it states:
Warning If you try to show the file picker while your app is snapped the file picker will not be shown and an exception will be thrown. You can avoid this by making sure your app is not snapped or by unsnapping it before you call the file picker.
I'm currently checking to see if the app is snapped or not, and my app responds differently in each case. My default behavior isn't showing the FileSavePicker, either, so I can't just try and then fall back to something else. Nor do I want to force the app to unsnap.
However, ApplicationViewState is deprecated post-8.1. In that documentation and related searching, developers are advised to access the window size directly in order to determine proper behavior. However, if the view state is no longer available, how do I know if the file picker will throw an exception or not? At what size is the app considered 'snapped'?
Also, I'm using C++, so an answer compatible with C++ would be splendid. I wouldn't mind seeing the C# solution, too.
回答1:
In regards to the FileSavePicker documentation - I believe that it is just an oversight. The text you quote was from the Windows 8 version, and to me it looks like it didn't get updated for Windows 8.1.
If you look at the FileOpenPicker documentation, you see that it was updated:
Important In Windows 8 if you attempt to display the file picker while your app is snapped, the file picker will not be shown and an exception will be thrown. You can avoid this by making sure your app is not snapped, or by unsnapping it before you call the file picker. ...Note that Windows 8.1 does not define a specific snapped window size. Instead, users can resize apps to any width, down to the minimum. Therefore, if your app will deploy only on Windows 8.1, you can ignore the EnsureUnsnapped function and calls to it in this topic's example code.
The last sentence (in bold) above essentially says that you can ignore state and safely open the file dialogs if you are running under Windows 8.1.
To test the above, I used VS 2012 to create a Windows 8 application with a file save picker (in C#). I believe the outcome will be the same with C++, but I am not 100% certain.
I should note that my test application does not check for view state and always tries to open a file dialog.
When the application is run under Windows 8 in the snapped state, the application causes an error. That same application (same binary) when run under Windows 8.1 allows the file save dialog to open without issue. As mentioned previously there is no snapped state in Windows 8.1, so the way I tested the application was to open the application to the minimum width (320 pixels).
To summarize:
- If you are targeting Windows 8.0, you will have to make sure the application is unsnapped prior to opening the file picker dialogs.
- If you are targeting Windows 8.1, you do not have to worry about state, as the file picker dialogs no longer throw any exceptions.
来源：https://stackoverflow.com/questions/25516313/filesavepicker-and-deprecated-applicationviewstate