What actually WM_IsVisible api checks?

Kusum Swarankar · Jul 23rd 2018, 12:12pm

hi I created a dialog box and took handle. On press of button in that dialog box new dialog will be created and previous one was deleted using GUI_EndDialog. now I want to check if the previous dialog box handle is valid or not for that i am checking WM_IsWindow() api. which will return 1 if window handle is valid else will return 0. which is fine.
When a handle got deleted but still it holds some value what is that value? is it an address or some value.
Before using WM_IsWindow() i used WM_IsVisible api but this api is returning 1 even if that handle is deleted. can you please explain the difference?

SEGGER - Schoenen · Jul 27th 2018, 10:20am

Hi,

The handle of a window holds a value we use internally to access its data through the emWin memory management. After deleting a window the handle has still the value (it doesn't gets zeroed). With WM_IsWindow() you can check if a handle with a value is valid. With WM_IsVisible() you can check whether a window is visible or not. Either hidden or completely covered by another window.

Regards,
Sven

Kusum Swarankar · Jul 30th 2018, 10:44am

Hi Schoenen thanks for the answer .
So even if i am deleting the window but WM_IsVisible() can still pass. But why the behavior is not same always, sometimes its passing the check and sometimes not.

SEGGER - Schoenen · Aug 3rd 2018, 2:55pm

Hi,

so you you pass the handle of a deleted window to the function WM_IsVisible()?

The return value can be anything if the window handle is not valid.

Regards,
Sven

Kusum Swarankar · Aug 6th 2018, 10:59am

ok Schoenen thanks.

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