自定义NSView拖动目标

Question

我正在尝试创建一个简单的NSView,它允许将Finder中的文件夹拖到它上面.文件夹路径是我希望视图作为可拖动项目接受的唯一内容.我一直在尝试遵循Apple文档,但到目前为止没有任何工作.到目前为止,我只是试图让视图适用于任何文件类型,但我似乎甚至无法做到这一点.这是我到目前为止所拥有的:

-(id) initWithFrame:(NSRect)frameRect
{
    if (self = [super initWithFrame:frameRect])
    {
        NSLog(@"getting called");
        [self registerForDraggedTypes:[NSArray arrayWithObjects:NSPasteboardTypeString,
                                       NSPasteboardTypePDF,
                                       NSPasteboardTypeTIFF,
                                       NSPasteboardTypePNG,
                                       NSPasteboardTypeRTF,
                                       NSPasteboardTypeRTFD,
                                       NSPasteboardTypeHTML,
                                       NSPasteboardTypeTabularText,
                                       NSPasteboardTypeFont,
                                       NSPasteboardTypeRuler,
                                       NSPasteboardTypeColor,
                                       NSPasteboardTypeSound,
                                       NSPasteboardTypeMultipleTextSelection,
                                       NSPasteboardTypeFindPanelSearchOptions, nil]];
    }
    return self;
}

-(BOOL) prepareForDragOperation: (id<NSDraggingInfo>) sender
{
    NSLog(@"preparing for drag");

    return YES;
}

该initWithFrame:方法被调用,但是当我尝试拖入视图时,该prepareForDragOperation:方法似乎永远不会被调用.我的问题:

1. 我究竟做错了什么？为什么prepareForDragOperation:永远不会被召唤？
2. 要使拖动操作仅支持拖动文件夹,我需要做什么？

更新

我registerForDraggedTypes:用我能找到的每种类型更新了我的方法.它现在看起来像这样:

[self registerForDraggedTypes:[NSArray arrayWithObjects:NSPasteboardTypeString,
                               NSPasteboardTypePDF,
                               NSPasteboardTypeTIFF,
                               NSPasteboardTypePNG,
                               NSPasteboardTypeRTF,
                               NSPasteboardTypeRTFD,
                               NSPasteboardTypeHTML,
                               NSPasteboardTypeTabularText,
                               NSPasteboardTypeFont,
                               NSPasteboardTypeRuler,
                               NSPasteboardTypeColor,
                               NSPasteboardTypeSound,
                               NSPasteboardTypeMultipleTextSelection,
                               NSPasteboardTypeFindPanelSearchOptions,
                               NSStringPboardType,
                               NSFilenamesPboardType,
                               NSPostScriptPboardType,
                               NSTIFFPboardType,
                               NSRTFPboardType,
                               NSTabularTextPboardType,
                               NSFontPboardType,
                               NSRulerPboardType,
                               NSFileContentsPboardType,
                               NSColorPboardType,
                               NSRTFDPboardType,
                               NSHTMLPboardType,
                               NSURLPboardType,
                               NSPDFPboardType,
                               NSVCardPboardType,
                               NSFilesPromisePboardType,
                               NSMultipleTextSelectionPboardType, nil]];

我注意到prepareForDragOperation:当我将文件夹拖到视图中时,没有调用该方法.我错过了一步吗？

Answer 1

这是一个符合这些标准的简单拖放视图:

MDDragDropView.h:

@interface MDDragDropView : NSView {
    BOOL        isHighlighted;
}

@property (assign, setter=setHighlighted:) BOOL isHighlighted;

@end

MDDragDropView.m:

@implementation MDDragDropView

@dynamic isHighlighted;

- (void)awakeFromNib {
    NSLog(@"[%@ %@]", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
    [self registerForDraggedTypes:[NSArray arrayWithObjects:NSFilenamesPboardType, nil]];
}

- (NSDragOperation)draggingEntered:(id <NSDraggingInfo>)sender {
    NSLog(@"[%@ %@]", NSStringFromClass([self class]), NSStringFromSelector(_cmd));

    NSPasteboard *pboard = [sender draggingPasteboard];

    if ([[pboard types] containsObject:NSFilenamesPboardType]) {

        NSArray *paths = [pboard propertyListForType:NSFilenamesPboardType];
        for (NSString *path in paths) {
            NSError *error = nil;
            NSString *utiType = [[NSWorkspace sharedWorkspace]
                                       typeOfFile:path error:&error];
            if (![[NSWorkspace sharedWorkspace] 
                      type:utiType conformsToType:(id)kUTTypeFolder]) {

                [self setHighlighted:NO];
                return NSDragOperationNone;
            }
        }
    }
    [self setHighlighted:YES];
    return NSDragOperationEvery;
}

其余的方法:

- (void)draggingExited:(id <NSDraggingInfo>)sender {
    [self setHighlighted:NO];
}


- (BOOL)prepareForDragOperation:(id <NSDraggingInfo>)sender  {
    return YES;
}

- (BOOL)performDragOperation:(id <NSDraggingInfo>)sender {
    [self setHighlighted:NO];
    return YES;
}
- (BOOL)isHighlighted {
    return isHighlighted;
}

- (void)setHighlighted:(BOOL)value {
    isHighlighted = value;
    [self setNeedsDisplay:YES];
}

- (void)drawRect:(NSRect)dirtyRect {
    [super drawRect:dirtyRect];
    if (isHighlighted) {
        [NSBezierPath setDefaultLineWidth:6.0];
        [[NSColor keyboardFocusIndicatorColor] set];
        [NSBezierPath strokeRect:self.frame];
    }
}

@end

prepareForDragOperation:没有被调用的原因是拖动目标序列遵循一组精确的步骤,如果前面的步骤没有实现,或者实现但是返回"停止拖动操作"类型的答案,后面的方法是永远达不到 (在您的情况下,您似乎没有实现该draggingEntered:方法,除了NSDragOperationNone在序列中继续之外,还需要返回其他内容).

在prepareForDragOperation:发送之前,视图首先发送一系列拖动目标消息:

单身- (NSDragOperation)draggingEntered:(id <NSDraggingInfo>)sender.

根据NSDragOperation从该方法返回的掩码,如果在您的类中实现了以下内容,则将调用以下内容:

多个- (NSDragOperation)draggingUpdated:(id <NSDraggingInfo>)sender.

根据NSDragOperation从该方法返回的掩码,然后prepareForDragOperation:将调用.