objective-c - 拖放创建拖动图像

Question

我正在为自定义 View 实现拖放；这个customView是NSView的子类并包含一些元素。当我开始对其进行拖动操作时，dragImage 它只是一个与 customView 大小相同的矩形灰色框。

这是我写的代码:

-(void) mouseDragged:(NSEvent *)theEvent
{
    NSPoint downWinLocation = [mouseDownEvent locationInWindow];
    NSPoint dragWinLocation = [theEvent locationInWindow];

    float distance = hypotf(downWinLocation.x - dragWinLocation.x, downWinLocation.y - downWinLocation.x);
    if (distance < 3) {
        return;
    }

    NSImage *viewImage = [self getSnapshotOfView];
    NSSize viewImageSize = [viewImage size];
    //Get Location of mouseDown event
    NSPoint p = [self convertPoint:downWinLocation fromView:nil];

    //Drag from the center of image
    p.x = p.x - viewImageSize.width / 2;
    p.y = p.y - viewImageSize.height / 2;

    //Write on PasteBoard
    NSPasteboard *pb = [NSPasteboard pasteboardWithName:NSDragPboard];
    [pb declareTypes:[NSArray arrayWithObject:NSFilenamesPboardType]
               owner:nil];
    //Assume fileList is list of files been readed
    NSArray *fileList = [NSArray arrayWithObjects:@"/tmp/ciao.txt", @"/tmp/ciao2.txt", nil];
    [pb setPropertyList:fileList forType:NSFilenamesPboardType];

    [self dragImage:viewImage at:p offset:NSMakeSize(0, 0) event:mouseDownEvent pasteboard:pb source:self slideBack:YES];
}

这是我用来创建快照的函数:

- (NSImage *) getSnapshotOfView
{
    NSRect rect = [self bounds] ;

    NSImage *image = [[[NSImage alloc] initWithSize: rect.size] autorelease];

    NSRect imageBounds;
    imageBounds.origin = NSZeroPoint;
    imageBounds.size = rect.size;

    [self lockFocus];
    NSBitmapImageRep *rep = [[NSBitmapImageRep alloc] initWithFocusedViewRect:imageBounds];
    [self unlockFocus];

    [image addRepresentation:rep];
    [rep release];

    return image;
}

这是我的自定义 View 上的拖动操作的图像(带有图标和标签“拖动我”的图像)

为什么我的dragImage只是一个灰色的框？

Answer 1

从您评论中的 IB 屏幕截图来看，您的 View 似乎是受层支持的。图层支持的 View 绘制到它们自己的图形区域，该区域与普通窗口支持存储分开。

这段代码:

[self lockFocus];
NSBitmapImageRep *rep = [[NSBitmapImageRep alloc] initWithFocusedViewRect:imageBounds];
[self unlockFocus];

从窗口后备存储中有效读取像素。由于您的 View 是受图层支持的，因此不会拾取其内容。

在没有图层支持的 View 的情况下尝试此操作。