Recently, I have seen following code appeared again and again in one of application written in Delphi:
begin
…
Screen.Cursor := crHourGlass;
try
…except
Screen.Cursor := crDefault;
…
end; {try}
Screen.Cursor := crDefault;
end;
This code works in most of the time, but it does have one issue, it makes an assumption that the cursor was crDefault thus it change the cursor back to default before the end. What if the cursor is not default before entering this code block? We can improve the code as following thus it will restore the cursor to what it is before this code block:
begin
…
LSavedCursor := Screen.Cursor;
Screen.Cursor := crHourGlass;
try
…except
Screen.Cursor := LSavedCursor;
…
end; {try}
Screen.Cursor := LSavedCursor;
end;
Or more proper way (in my opinion) is to use a try … finally block to protect the code block and it will guarantee the cursor will be restored:
begin
…
LSavedCursor := Screen.Cursor;
Screen.Cursor := crHourGlass;
try
try
… //doing busy business code insert hereexcept
…
end; {try}finally
Screen.Cursor := LSavedCursor;end;
end;
Can it be improved further? The answer is YES and NO. If you are still using Delphi earlier than Delphi 2009, then the answer is NO, because we are going to use Anonymous Method which was introduced by Delphi 2009 and later version of Delphi.
With above code, you actually need to define the local variable LSaveCursor in each method in which it has above code, so it is a bit trivial, and you cannot refactoring above code to a method because the actually doing busy business code is vary from method to method, refactoring each doing busy business code to a method and then pass the method’s point will be a over kill approach. But with anonymous method, we don’t need to refactoring doing busy business code to a method, instead, we can pass the code as an anonymous method.
First we need to create a procedure to take care the logic for changing the cursor to hour glass and restore it when it completes. Below is the procedure:
procedure BusyDoing (AProc:TProc);
var
LSavedCursor : TCursor;
begin
LSavedCursor := Screen.Cursor;
Screen.Cursor := crHourGlass;
try
AProc;
finally
Screen.Cursor := LSavedCursor;
end;
end;
This procedure has one parameter AProc which is a pre-defined anonymous method which is defined in unit System.SysUtils as
TProc = reference to procedure;
To use this procedure, all we need to do is enclose the doing busy business code as an anonymous method like this:
BusyDoing(
procedure
begin
… //doing busy business code insert hereend
);
That is it, very neat, isn’t it?
