Creating an Accessory NSView

An accessory view is an NSView that you provide to the NSSavePanel object. The NSSavePanel object is then automatically incorporated into the Save sheet when it is displayed. Many applications use accessory views to let the user choose options when saving.

IB has direct support for creating accessory views. It allows you to create standalone views — views that aren’t displayed in a window, but that are designed to be placed into windows as the need arises. In the next step, we’ll create a simple NSView instance that will be used as a container. We will then place the desired controls in this NSView and group it in a box. Finally, we will take the id of this view and pass it to the NSSavePanel object.

We’ll start by making the necessary changes to Controller.h. Then we’ll create the accessory view and make connections in IB. Finally, we’ll implement the necessary method in Controller.m to allow us to specify the file type.

  1. Insert the formatBox and formatMatrix outlets and the savePanel instance variable into Controller.h: 

    @interface Controller : NSObject
{
    IBOutlet id graphView;
    IBOutlet id prefController;
    IBOutlet  id  formatBox;
                         IBOutlet  id  formatMatrix;
                         NSSavePanel  *savePanel;
}

  2. Insert the following setFormat: action method declaration into Controller.h: 

                         - (IBAction)setFormat:(id)sender;

  3. Save Controller.h.

  4. Activate IB and make sure that MainMenu.nib is the active window.

  5. Read (parse) the updated Controller class definition into MainMenu.nib.

    An easy way to do this is to drag the Controller.h icon from PB’s Groups & Files pane into the MainMenu.nib window in IB. Check the Info dialog to make sure that the newly added action method and outlets are in the Controller class of MainMenu.nib.

Next, we’ll create the accessory NSView.

  1. Drag a CustomView icon from IB’s Cocoa-Containers palette and drop it into the MainMenu.nib window, as shown in Figure 19-14.

    Dragging a CustomView from the Cocoa-Containers palette into the MainMenu.nib window

    Figure 19-14. Dragging a CustomView from the Cocoa-Containers palette into the MainMenu.nib window

    A new NSView will be added to the file MainMenu.nib and a small window titled “View” will appear, as shown in Figure 19-15. This odd-looking window represents the accessory view. The icon titled “View” in the Nib File window represents the accessory view window.

Accessory view window (left) and its icon representation (right)

Figure 19-15. Accessory view window (left) and its icon representation (right)

  1. Drag a radio-button matrix from IB’s Cocoa-Views palette and drop it in the accessory view. Allow two radio-button choices, PDF and TIFF, with PDF the default. Change the font of the radio-button labels if you like.

  2. Select the radio-button matrix and choose IB’s Layout → Make subviews of → Box menu command to group it in a box.

  3. Change the title of the box to “Format” in the Info dialog. The window should now look very similar to the one in Figure 19-16.

The completed accessory view in IB

Figure 19-16. The completed accessory view in IB

  1. Connect the Controller’s formatBox outlet to the box titled “Format”.

  2. Connect the Controller’s formatMatrix outlet to the radio-button matrix, as shown in Figure 19-17. Refer to the text near the bottom of the Info dialog, and verify that each outlet was connected to the correct object.

Connection (formatMatrix) from Controller to radio-button matrix

Figure 19-17. Connection (formatMatrix) from Controller to radio-button matrix

  1. Connect the radio-button matrix to the Controller instance icon so that it sends the setFormat: action. Again, be sure to connect the NSMatrix and not the containing box (check the title of the Info dialog). Note that this connection is in the opposite direction of the one in the previous step.

Changes to the Controller Class

In addition to the PDFForView: and TIFFForView: methods we discussed earlier, we’ll need to implement a setFormat: action method that is invoked when the user changes the file-format type in the Save panel. Cocoa provides only a single instance of the NSSavePanel object, so we can use the [SavePanel new] statement to get the panel’s id. We’ll do that later, in the saveDocumentTo method. The SavePanel object lets us change its required file types inside its modal loop, so when the user changes the format, the required file type is automatically changed.

  1. Insert the following setFormat: method into Controller.m: 

                            - (IBAction)setFormat:(id)sender
                        {
                            savePanel = [NSSavePanel savePanel];
                            [savePanel setRequiredFileType:
                                [ [[sender selectedCell] title] lowercaseString] ];
                        }

It’s a complicated statement, but by now you should be able to figure it out on your own. Notice that we directly read the title of the selected cell in the matrix, so you can add new file types simply by adding their extensions to the control.

Now we need to modify thesaveDocumentTo: method to rip the box (and the subviews that it contains) out of the window we created earlier and put it into the Save panel as an accessory NSView. This is done with the NSSavePanel’s setAccessoryView: method. The NSSavePanel object automatically resizes the on-screen Save panel (sheet) to accommodate the accessory NSView. We need to modify the save: method to look at the title of the selected cell and choose the appropriate method to send output to the stream. And finally, we need to modify the savePanelDidEnd:returnCode:contextInfo: method so that it looks at the selected file type and picks the appropriate format. All of these modifications are presented in the following steps.

  1. Replace the previous version of the savePanelDidEnd:returnCode:contextInfo: method in Controller.m with the following one: 

                            - (void)savePanelDidEnd:(NSSavePanel *)sheet
                                     returnCode:(int)returnCode
                                    contextInfo:(void  *)contextInfo
                        {
                            NSData *image=0;
                            NSString *filetype = [sheet requiredFileType];
                        
    if (returnCode==0) return;    // User did not click OK
                        
    if ([filetype isEqualToString:@"pdf"]) {
                                image = [self PDFForView:graphView];
                            }
                        
    if ([filetype isEqualToString:@"tiff"]) {
                                image = [self TIFFForView:graphView];
                            }
                        
    if (image==0) {
                                NSRunAlertPanel(nil,@"Unknown file type '%@'",
                                                nil,nil,nil,filetype);
                                return;
                            }
                        
    if ([image writeToFile:[sheet filename] atomically:NO]==NO) {
                                NSRunAlertPanel(nil,@"Cannot save file '%@': %s",nil,nil,nil,
                                                [sheet filename],strerror(errno));
                            }
                        }

  2. Replace the previous version of the saveDocumentTo: method in Controller.m with the following one: 

                            - (IBAction)saveDocumentTo:(id)sender
                        {
                            NSString    *type = [ [ [formatMatrix selectedCell] title]
                                                     lowercaseString];
                        
    // Get a Save panel
                            savePanel = [NSSavePanel savePanel];
                            [savePanel setTitle:@"Save Graph Image"];
                        
    // Set the initial file type
                            [savePanel setRequiredFileType:type];
                        
    // Put the format box in the Save Panel
                            [savePanel setAccessoryView:formatBox];
                        
    [formatBox retain];                 // Keep a copy!
                        
    // And run
                            [savePanel beginSheetForDirectory:nil
                                                         file:nil
                                               modalForWindow:[graphView window]
                                                modalDelegate:self
                                didEndSelector:@selector(savePanelDidEnd:returnCode:contextInfo:)
                                                  contextInfo:nil];
                        }

Note that this method retains the formatBox instance variable. This is necessary because the savePanel automatically releases its accessory view. If the Controller class does not retain the formatBox, it will be freed, and an error will be generated the next time the Save panel (sheet) is displayed.

Testing the PDF and TIFF Save Feature

  1. Build and run GraphPaper, saving all files first.

  2. Click the Graph button, then choose the Save Graph menu command. You should see a Save panel with the accessory NSView containing the radio-button matrix, as shown in Figure 19-18.

Save sheet with an accessory NSView (Format box)

Figure 19-18. Save sheet with an accessory NSView (Format box)

  1. Try saving the same graph as PDF and as TIFF. Then double-click the PDF and TIFF file icons in your Finder to see them in Preview. You might also try to import the files into a word processor or other application.

  2. Quit GraphPaper.

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