Cocoa QuickLook initiated by NSTableView Cell

问题

I have an NSTableView that contains 2 different Columns - one is an NSImageCell that shows a file icon, and the second is a custom subclass of NSTextFieldCell that contains a quick look button on the right of the text. When I click the Quick Look button, the following code is invoked:

[[QLPreviewPanel sharedPreviewPanel] makeKeyAndOrderFront:nil];

This does it's job and shows the blank Quick Look panel saying "No Items Selected." After I did a bit of research on the internet, I implemented a custom NSTableView subclass to be the Delegate and Data Source for the Quick Look panel. I get the notification that Quick Look asks if I want to be the delegate, and I respond with return YES. Even though I implement all methods in both QLPreviewPanelDataSource and QLPreviewPanelDelegate, at runtime I get this error on the console:

2010-12-24 15:32:17.235 BackMeUp[4763:80f] clicked: ~/Desktop/HUDTape.mov
2010-12-24 15:32:17.489 BackMeUp[4763:80f] [QL] QLError(): -[QLPreviewPanel setDelegate:] called while the panel has no controller - Fix this or this will raise soon.
See comments in QLPreviewPanel.h for -acceptsPreviewPanelControl:/-beginPreviewPanelControl:/-endPreviewPanelControl:.
2010-12-24 15:32:17.490 BackMeUp[4763:80f] [QL] QLError(): -[QLPreviewPanel setDataSource:] called while the panel has no controller - Fix this or this will raise soon.
See comments in QLPreviewPanel.h for -acceptsPreviewPanelControl:/-beginPreviewPanelControl:/-endPreviewPanelControl:.
2010-12-24 15:32:17.491 BackMeUp[4763:80f] We can now receive QL Events.
2010-12-24 15:32:18.291 BackMeUp[4763:80f] -[NSPathStore2 stringValue]: unrecognized selector sent to instance 0x5ecb10
2010-12-24 15:32:18.292 BackMeUp[4763:80f] -[NSPathStore2 stringValue]: unrecognized selector sent to instance 0x5ecb10

And the Quick Look panel does not show up, which I find rather odd. The first line above is just that I know the cell has been clicked. Anyways, here is the .m file of the custom table view subclass:

//
//  BackupListTableView.m
//  BackMeUp
//
//  Created by Tristan Seifert on 12/24/10.
//  Copyright 2010 24/7 Server. All rights reserved.
//

#import "BackupListTableView.h"


@implementation BackupListTableView

- (void) awakeFromNib {

}

// Quick Look Delegates

- (BOOL)acceptsPreviewPanelControl:(QLPreviewPanel *)panel;
{
    [QLPreviewPanel sharedPreviewPanel].delegate = self;
    [QLPreviewPanel sharedPreviewPanel].dataSource = self;

    NSLog(@"We can now receive QL Events.");

    return YES;
}

- (void)beginPreviewPanelControl:(QLPreviewPanel *)panel
{
    // This document is now responsible of the preview panel
    // It is allowed to set the delegate, data source and refresh panel.
    [QLPreviewPanel sharedPreviewPanel].delegate = self;
    [QLPreviewPanel sharedPreviewPanel].dataSource = self;
}

- (void)endPreviewPanelControl:(QLPreviewPanel *)panel
{
    // This document loses its responsisibility on the preview panel
    // Until the next call to -beginPreviewPanelControl: it must not
    // change the panel's delegate, data source or refresh it.
    return;
}

// Quick Look panel data source

- (NSInteger)numberOfPreviewItemsInPreviewPanel:(QLPreviewPanel *)panel
{
    return 1;
}

- (id <QLPreviewItem>)previewPanel:(QLPreviewPanel *)panel previewItemAtIndex:(NSInteger)index
{
    int selectedRow = [self selectedRow];


    return [NSURL URLWithString:[[[self dataSource] tableView:self objectValueForTableColumn:fileColumn row:selectedRow] stringValue]];
}

// Quick Look panel delegate

- (BOOL)previewPanel:(QLPreviewPanel *)panel handleEvent:(NSEvent *)event
{
    // redirect all key down events to the table view

    return NO;
}

// This delegate method provides the rect on screen from which the panel will zoom.
- (NSRect)previewPanel:(QLPreviewPanel *)panel sourceFrameOnScreenForPreviewItem:(id <QLPreviewItem>)item
{

    NSRect iconRect = [self rectOfColumn:1];
    /*
     // check that the icon rect is visible on screen
     NSRect visibleRect = [self visibleRect];


     // convert icon rect to screen coordinates
     iconRect = [self convertRectToBase:iconRect];
     iconRect.origin = [[self window] convertBaseToScreen:iconRect.origin];
     */
    return iconRect;
}

// This delegate method provides a transition image between the table view and the preview panel
- (id)previewPanel:(QLPreviewPanel *)panel transitionImageForPreviewItem:(id <QLPreviewItem>)item contentRect:(NSRect *)contentRect
{
    int selectedRow = [self selectedRow];

    NSImage *fileIcon = [[NSWorkspace sharedWorkspace] iconForFile:[[[self dataSource] tableView:self objectValueForTableColumn:fileColumn row:selectedRow] stringValue]];

    return fileIcon;
}

@end

Thanks for any help.

回答1:

The documentation isn't the best for this, since it's a new feature that was added in 10.6. (Well, there is obviously the class and protocol references, but in my experience, I've always found the Companion Guides to be more helpful in understanding how the objects are intended to be used in a real-world scenario).

The QLPreviewPanelController Protocol Reference defines 3 methods:

QLPreviewPanelController Protocol Reference

The Quick Look preview panel shows previews for items provided by the first object in the responder chain that implements the methods in this protocol. You typically implement these methods in your window controller or delegate. You should never try to modify preview panel state if you’re not controlling the panel.

- (BOOL)acceptsPreviewPanelControl:(QLPreviewPanel *)panel;

- (BOOL)beginPreviewPanelControl:(QLPreviewPanel *)panel;

- (void)endPreviewPanelControl:(QLPreviewPanel *)panel;

I'm guessing that your code should look like this:

- (BOOL)acceptsPreviewPanelControl:(QLPreviewPanel *)panel
{
    return YES;
}

You shouldn't be doing anything in that method besides returning YES. acceptsPreviewPanelControl: is sent to every object in the responder chain until something returns YES. By returning YES, that object effectively becomes "the controller". The latter 2 methods are called on the controller object after it returns YES from the first method. So you should only be setting the delegate and datasource in the beginPreviewPanelControl: method (at which time you will be regarded as the current controller).

- (void)beginPreviewPanelControl:(QLPreviewPanel *)panel
{

    // This document is now responsible of the preview panel
    // It is allowed to set the delegate, data source and refresh panel.

    [QLPreviewPanel sharedPreviewPanel].delegate = self;
    [QLPreviewPanel sharedPreviewPanel].dataSource = self;

    NSLog(@"We can now receive QL Events.");
}

回答2:

First:

-acceptsPreviewPanelControl should only return YES and not try to set delegate and datasource.

Then, the problem is that you get an exception breaking the panel:

2010-12-24 15:32:18.291 BackMeUp[4763:80f] -[NSPathStore2 stringValue]: unrecognized selector sent to instance 0x5ecb10

The exception is very likely caused by these invocations:

[[[self dataSource] tableView:self objectValueForTableColumn:fileColumn row:selectedRow] stringValue]

Very likely, [[self dataSource] tableView:self objectValueForTableColumn:fileColumn row:selectedRow] is a file path (a NSPathStore instance which is a subclass of NSString) so it does not respond to -stringValue

So replace:

[NSURL URLWithString:[[[self dataSource] tableView:self objectValueForTableColumn:fileColumn row:selectedRow] stringValue]]

by:

[NSURL fileURLWithPath:[[self dataSource] tableView:self objectValueForTableColumn:fileColumn row:selectedRow]]

Also remove the call to -stringValue in transitionImageForPreviewItem.

As a side note, it seems to be suboptimal to load the image at each call of transitionImageForPreviewItem. I suppose you already have the image computed elsewhere (displayed in your table view), try to use it.

来源：https://stackoverflow.com/questions/4528732/cocoa-quicklook-initiated-by-nstableview-cell

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