NSView的拖放委托无法设置属性

Question

我使用NSView委托来读取拖动的excel值。为此，我创建了NSView的子类。我的代码是这样的-

@interface SSDragDropView : NSView
    {
        NSString *textToDisplay;
    }
    @property(nonatomic,retain) NSString *textToDisplay; // setters/getters

    @synthesize textToDisplay;// setters/getters

    @implementation SSDragDropView
    - (NSDragOperation)draggingEntered:(id <NSDraggingInfo>)sender{
        [self setNeedsDisplay: YES];
        return NSDragOperationGeneric;
    }

    - (void)draggingExited:(id <NSDraggingInfo>)sender{
        [self setNeedsDisplay: YES];
    }

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


   - (BOOL)performDragOperation:(id < NSDraggingInfo >)sender {
        NSArray *draggedFilenames = [[sender draggingPasteboard] propertyListForType:NSFilenamesPboardType];
        if ([[[draggedFilenames objectAtIndex:0] pathExtension] isEqual:@"xls"]){
            return YES;
        } else {
            return NO;
        }
    }

    - (void)concludeDragOperation:(id <NSDraggingInfo>)sender{
        NSArray *draggedFilenames = [[sender draggingPasteboard] propertyListForType:NSFilenamesPboardType];
        NSURL *url =   [NSURL fileURLWithPath:[draggedFilenames objectAtIndex:0]];
       NSString *textDataFile = [NSString stringWithContentsOfURL:url usedEncoding:nil error:nil]; //This text is the original excel text and its getting displayed.
    [self setTextToDisplay:textDataFile];
       }

我将textDataFile值设置为该类的字符串属性。现在，我在其他类中使用SSDragDropView属性值，比如-

SSDragDropView *dragView = [SSDragDropView new];
    NSLog(@"DragView Value is %@",[dragView textToDisplay]); 

但是我每次都会得到null。就像我不能在那些委托方法中设置属性值一样吗？

Answer 1

上面的问题可以通过在SSDraDropView.h类中声明一个全局变量来解决。

#import <Cocoa/Cocoa.h>
NSString *myTextToDisplay;
@interface SSDragDropView : NSView
{

可以在所需的委托方法中设置相同的值

- (void)concludeDragOperation:(id <NSDraggingInfo>)sender {

// .... //Your Code
NSString *textDataFile = [NSString stringWithContentsOfURL:url usedEncoding:nil error:nil];
myTextToDisplay = textDataFile;
// .... //Your Code
}

:)

Answer 2

添加

[dragView registerForDraggedTypes:[NSArray arrayWithObjects:NSFilenamesPboardType, nil]];  

- (NSDragOperation)draggingEntered:(id <NSDraggingInfo>)sender{

    NSPasteboard *pboard = [sender draggingPasteboard];
    NSArray *paths = [pboard propertyListForType:NSFilenamesPboardType];
    NSLog(@"%@",paths);
    [self setNeedsDisplay: YES];
    return NSDragOperationGeneric;
}  

下面的代码将打印为空，因为您没有在NSView上拖动任何内容。

SSDragDropView *dragView = [SSDragDropView new];
    NSLog(@"DragView Value is %@",[dragView textToDisplay]);