How can I make my Android app react to the back-button?
Is there something as high-level VCL's TApplicationEvents to handle it, or do I need to dive deep into low-level Android-specific stuff here?
Right now, most of the demo applications have an on-screen back button to go back to a previous screen. Pressing the psysical button always seems to quit the app, and in some situations it results in an access violation.
In the form's OnKey...
events, the Key
parameter is vkHardwareBack
on Android. For example:
uses
FMX.Platform, FMX.VirtualKeyboard;
procedure TForm1.FormKeyUp(Sender: TObject; var Key: Word; var KeyChar: Char; Shift: TShiftState);
var
FService : IFMXVirtualKeyboardService;
begin
if Key = vkHardwareBack then
begin
TPlatformServices.Current.SupportsPlatformService(IFMXVirtualKeyboardService, IInterface(FService));
if (FService <> nil) and (vksVisible in FService.VirtualKeyBoardState) then
begin
// Back button pressed, keyboard visible, so do nothing...
end else
begin
// Back button pressed, keyboard not visible or not supported on this platform, lets exit the app...
if MessageDlg('Exit Application?', TMsgDlgType.mtConfirmation, [TMsgDlgBtn.mbOK, TMsgDlgBtn.mbCancel], -1) = mrOK then
begin
// Exit application here...
end else
begin
// They changed their mind, so ignore the Back button press...
Key := 0;
end;
end;
end
...
end;
Here is an updated code for Remy's answer (works with Seattle):
procedure TForm1.FormKeyUp(Sender: TObject; var Key: Word; var KeyChar: Char; Shift: TShiftState);
var
FService : IFMXVirtualKeyboardService;
begin
if Key = vkHardwareBack then
begin
TPlatformServices.Current.SupportsPlatformService(IFMXVirtualKeyboardService, IInterface(FService));
if (FService <> nil) and (TVirtualKeyboardState.Visible in FService.VirtualKeyBoardState) then
begin
// Back button pressed, keyboard visible, so do nothing...
end else
begin
Key := 0;
// Back button pressed, keyboard not visible or not supported on this platform, lets exit the app...
MessageDlg('Exit Application?', TMsgDlgType.mtConfirmation, [TMsgDlgBtn.mbOK, TMsgDlgBtn.mbCancel], -1, OnCloseDialog);
end;
end;
end;
procedure TForm1.OnCloseDialog(Sender: TObject; const AResult: TModalResult);
begin
if AResult = mrOK then
Close;
end;
For future reference to anyone trying to make sense of this..
if Key = vkHardwareBack then
begin
// your code here
key := 0;
end;
The key := 0; is the secret to stop the app from closing..
This goes in the forms OnKeyUp event
Going back to the previous screen depends on your application design.
If you used TTabControl
for displaying pages, you can navigate to the previous TTabItem
.
If you used TForms
for displaying pages, you must use Close()
procedure for closing the current form and going back to the previous screen.
Try this:
uses FMX.Platform,FMX.VirtualKeyboard,FMX.Helpers.Android;
procedure THeaderFooterForm.FormKeyUp(Sender: TObject; var Key: Word;
var KeyChar: Char; Shift: TShiftState);
var FService : IFMXVirtualKeyboardService;
begin
if Key = vkHardwareBack then
begin
TPlatformServices.Current.SupportsPlatformService(IFMXVirtualKeyboardService, IInterface(FService));
if (FService <> nil) and (vksVisible in FService.VirtualKeyBoardState) then
begin
// Back button pressed, keyboard visible, so do nothing...
end
else
begin
if MessageDlg('Exit Application?', TMsgDlgType.mtConfirmation, [TMsgDlgBtn.mbOK, TMsgDlgBtn.mbCancel], -1) = mrOK then
begin
// Exit application here...
SharedActivity.Finish;
end;
end;
end
else
// Menu button pressed
if Key = sgiUpRightLong then
begin
showmessage('Menu button pressed');
end;
end;
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