CopyFromScreen - check if handle is vaild
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I'm capturing screen using CopyFromScreen. When someone locks PC, then it's starting to throw exception System.ComponentModel.Win32Exception (0x80004005): The handle is invalid. To avoid it, I'm checking current session state using SystemState.SessionSwitch. It's a good solution, but when I'm capturing screen with speed 30 screenshots per second, then it is fast enough to fire this exception 1/2 times before I switch flag state in SessionSwitch event. Is there any way to check current session state in catch block or to check if handle is valid before I invoke CopyFromScreen?
c# winapi gdi system.drawing
asked Nov 23 '18 at 13:36
HawexHawex
8810
add a comment |
I'm capturing screen using CopyFromScreen. When someone locks PC, then it's starting to throw exception System.ComponentModel.Win32Exception (0x80004005): The handle is invalid. To avoid it, I'm checking current session state using SystemState.SessionSwitch. It's a good solution, but when I'm capturing screen with speed 30 screenshots per second, then it is fast enough to fire this exception 1/2 times before I switch flag state in SessionSwitch event. Is there any way to check current session state in catch block or to check if handle is valid before I invoke CopyFromScreen?
c# winapi gdi system.drawing
asked Nov 23 '18 at 13:36
HawexHawex
8810
2
Not being able to reliably tell that the user activated the secure desktop is a feature. SessionSwitch squeaked past the security review, somehow, it did get added much later. You might get a better indication from Control.CreateGraphics() producing IntPtr.Zero for the GetHdc() return value. Not sure, try/catch is otherwise as good as it is going to get.
– Hans Passant
Nov 23 '18 at 13:56
Thanks! I'm checking now value from GetHdc() and it seems to be working great! As this answer is in comment I don't know how to mark it as accepted answer. Is it possible in any way :)?
– Hawex
Nov 23 '18 at 14:36
Lucky guess. Be sure to share what you discovered in your own post and mark it as the answer.
– Hans Passant
Nov 23 '18 at 14:39
add a comment |
I'm capturing screen using CopyFromScreen. When someone locks PC, then it's starting to throw exception System.ComponentModel.Win32Exception (0x80004005): The handle is invalid. To avoid it, I'm checking current session state using SystemState.SessionSwitch. It's a good solution, but when I'm capturing screen with speed 30 screenshots per second, then it is fast enough to fire this exception 1/2 times before I switch flag state in SessionSwitch event. Is there any way to check current session state in catch block or to check if handle is valid before I invoke CopyFromScreen?
c# winapi gdi system.drawing
asked Nov 23 '18 at 13:36
HawexHawex
8810
I'm capturing screen using CopyFromScreen. When someone locks PC, then it's starting to throw exception System.ComponentModel.Win32Exception (0x80004005): The handle is invalid. To avoid it, I'm checking current session state using SystemState.SessionSwitch. It's a good solution, but when I'm capturing screen with speed 30 screenshots per second, then it is fast enough to fire this exception 1/2 times before I switch flag state in SessionSwitch event. Is there any way to check current session state in catch block or to check if handle is valid before I invoke CopyFromScreen?
c# winapi gdi system.drawing
c# winapi gdi system.drawing
asked Nov 23 '18 at 13:36
HawexHawex
8810
asked Nov 23 '18 at 13:36
HawexHawex
8810
asked Nov 23 '18 at 13:36
HawexHawex
8810
asked Nov 23 '18 at 13:36
HawexHawex
8810
asked Nov 23 '18 at 13:36
HawexHawex
8810
8810
2
Not being able to reliably tell that the user activated the secure desktop is a feature. SessionSwitch squeaked past the security review, somehow, it did get added much later. You might get a better indication from Control.CreateGraphics() producing IntPtr.Zero for the GetHdc() return value. Not sure, try/catch is otherwise as good as it is going to get.
– Hans Passant
Nov 23 '18 at 13:56
Thanks! I'm checking now value from GetHdc() and it seems to be working great! As this answer is in comment I don't know how to mark it as accepted answer. Is it possible in any way :)?
– Hawex
Nov 23 '18 at 14:36
Lucky guess. Be sure to share what you discovered in your own post and mark it as the answer.
– Hans Passant
Nov 23 '18 at 14:39
add a comment |
2
Not being able to reliably tell that the user activated the secure desktop is a feature. SessionSwitch squeaked past the security review, somehow, it did get added much later. You might get a better indication from Control.CreateGraphics() producing IntPtr.Zero for the GetHdc() return value. Not sure, try/catch is otherwise as good as it is going to get.
– Hans Passant
Nov 23 '18 at 13:56
Thanks! I'm checking now value from GetHdc() and it seems to be working great! As this answer is in comment I don't know how to mark it as accepted answer. Is it possible in any way :)?
– Hawex
Nov 23 '18 at 14:36
Lucky guess. Be sure to share what you discovered in your own post and mark it as the answer.
– Hans Passant
Nov 23 '18 at 14:39
2
2
Not being able to reliably tell that the user activated the secure desktop is a feature. SessionSwitch squeaked past the security review, somehow, it did get added much later. You might get a better indication from Control.CreateGraphics() producing IntPtr.Zero for the GetHdc() return value. Not sure, try/catch is otherwise as good as it is going to get.
– Hans Passant
Nov 23 '18 at 13:56
Not being able to reliably tell that the user activated the secure desktop is a feature. SessionSwitch squeaked past the security review, somehow, it did get added much later. You might get a better indication from Control.CreateGraphics() producing IntPtr.Zero for the GetHdc() return value. Not sure, try/catch is otherwise as good as it is going to get.
– Hans Passant
Nov 23 '18 at 13:56
Thanks! I'm checking now value from GetHdc() and it seems to be working great! As this answer is in comment I don't know how to mark it as accepted answer. Is it possible in any way :)?
– Hawex
Nov 23 '18 at 14:36
Thanks! I'm checking now value from GetHdc() and it seems to be working great! As this answer is in comment I don't know how to mark it as accepted answer. Is it possible in any way :)?
– Hawex
Nov 23 '18 at 14:36
Lucky guess. Be sure to share what you discovered in your own post and mark it as the answer.
– Hans Passant
Nov 23 '18 at 14:39
Lucky guess. Be sure to share what you discovered in your own post and mark it as the answer.
– Hans Passant
Nov 23 '18 at 14:39
add a comment |
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2
Not being able to reliably tell that the user activated the secure desktop is a feature. SessionSwitch squeaked past the security review, somehow, it did get added much later. You might get a better indication from Control.CreateGraphics() producing IntPtr.Zero for the GetHdc() return value. Not sure, try/catch is otherwise as good as it is going to get.
– Hans Passant
Nov 23 '18 at 13:56
Thanks! I'm checking now value from GetHdc() and it seems to be working great! As this answer is in comment I don't know how to mark it as accepted answer. Is it possible in any way :)?
– Hawex
Nov 23 '18 at 14:36
Lucky guess. Be sure to share what you discovered in your own post and mark it as the answer.
– Hans Passant
Nov 23 '18 at 14:39