Opening+a+file+by+dropping+or+clicking

//by Richard Russell, October 2007//

In Windows, some common ways of opening a file (for example a **document** or **image** file) are as follows:
 * **Drag-and-drop** the file onto the icon of the application you want to open it.
 * **Right-click** on the file's icon and select **Open With** from the menu.
 * **Right-click** on the file's icon and select **Send To** from the menu.
 * **Double-click** on the file's icon (it will be opened by the default viewer for that file type).

You may want your own BBC BASIC program to be able to open a file in one of these ways. That is easily achieved because in each case what happens is that the selected application is executed with the //path and name to the selected file// in the command line. So all you need to do in your program is extract the contents of the **@cmd$** system variable and use that as the path/name of the file to be opened.

There is just one minor complication. If the path or name of the file contains spaces, Windows encloses the entire **@cmd$** string in quotation marks ("). Your program must remove those before the the path/filename is suitable for use.

Here is a very simple program which displays a BMP file:

code format="bb4w" bmpfile$ = @cmd$ IF ASC(bmpfile$)=34 bmpfile$=EVAL(bmpfile$) OSCLI "DISPLAY """+bmpfile$+"""" code The first line copies the contents of **@cmd$** (since you must not attempt to modify the contents of that variable). The second line examines the path/filename and if it is enclosed in quotation marks they are stripped off. The third line displays the image; note the addition of quotation marks. It may seem strange to strip off the quotes and then put them back again, but that ensures that the contents of **bmpfile$** are in a suitable form whenever a valid path/filename is needed (for example in an **OPENIN** function).

Of course this only works when you have 'compiled' your program to a standalone executable, since only then can your program be executed by Windows in this way. When testing your program in the Interactive Development Environment **@cmd$** will contain an empty string. You may therefore wish to add to your program so that in these circumstances it requests the filename, for example:

code format="bb4w" bmpfile$ = @cmd$ IF ASC(bmpfile$)=34 bmpfile$=EVAL(bmpfile$) IF bmpfile$ = "" THEN bmpfile$ = FNrequestfile OSCLI "DISPLAY """+bmpfile$+"""" code Here **FNrequestfile** is assumed to prompt the user to enter (or select) a filename, perhaps by means of an [|INPUT] statement or by using the Windows [|GetOpenFileName] dialogue.

To add your compiled application to the **Send To** list you need to place a shortcut there as follows:
 * 1) Click **Start**, and then click **Run**.
 * 2) In the Open box, type, and then click **OK**.
 * 3) Add a destination by doing one of the following:
 * Right-drag your application into the SendTo folder, and select 'Create shortcut here'.
 * Select File... New and then click Shortcut.

To make your application the default viewer for a specific file type you will need to edit the file **associations**. You can do that as follows:
 * 1) Open **My Computer** or **Windows Explorer**.
 * 2) Select Tools... Folder Options... File Types.
 * 3) Select the appropriate extension from the list.
 * 4) Click the **Change** button.
 * 5) Select your application from the list.
 * 6) Confirm with **OK**.