objective-c - CALayer 不显示

Question

在尝试制作可拖动的 CALayer ( Question on Stack Overflow here ) 时，我尝试通过代码创建一个窗口并向其中添加一个 CALayer，但我不明白为什么它没有显示。

NSRect rect = NSZeroRect;
    rect.size = NSMakeSize( SSRandomFloatBetween( 300.0, 200.0 ), SSRandomFloatBetween( 300.0, 200.0 ));

    NSWindow *newWin = [[NSWindow alloc] initWithContentRect:rect styleMask:NSBorderlessWindowMask backing:NSWindowBackingLocationDefault defer:YES];
    [newWin setBackgroundColor: [NSColor clearColor]];
    [newWin setOpaque:NO];
    [newWin setIgnoresMouseEvents:NO];
    [newWin setMovableByWindowBackground:YES];
    [newWin makeKeyAndOrderFront:self];

    [[newWin contentView] setWantsLayer:YES];

    NSRect contentFrame = [[newWin contentView] frame];
    CALayer *newWinLayer = [CALayer layer];
    newWinLayer.frame = NSRectToCGRect(contentFrame);

    layer.backgroundColor=CGColorCreateGenericGray(0.0f, 0.5f);
    layer.borderColor=CGColorCreateGenericGray(0.756f, 0.5f);
    layer.borderWidth=5.0;

        // Calculate random origin point
    rect.origin = SSRandomPointForSizeWithinRect( rect.size, [window frame] );

        // Set the layer frame to our random rectangle.
    layer.frame = NSRectToCGRect(rect);
    layer.cornerRadius = 25.0f;
  [newWinLayer addSublayer:layer];

“窗口”链接到一个大窗口，其中有一个半透明(黑色填充)窗口，可调整大小以填充屏幕。

我已经使窗口可拖动，但为什么窗口中的 CALayer 没有显示？

Answer 1

NSRect rect = NSZeroRect;

rect.size = NSMakeSize( SSRandomFloatBetween( 300.0, 200.0 ),
      SSRandomFloatBetween( 300.0, 200.0 ));

NSWindow *newWin = [[NSWindow alloc] initWithContentRect:rect
            styleMask:NSBorderlessWindowMask
           backing:NSWindowBackingLocationDefault defer:YES];

[newWin setBackgroundColor:[NSColor clearColor]];
[newWin setOpaque:NO];
[newWin setIgnoresMouseEvents:NO];
[newWin setMovableByWindowBackground:YES];
[newWin makeKeyAndOrderFront:self];

// you don't want to do this yet
// [[newWin contentView] setWantsLayer:YES];

NSRect contentFrame = [[newWin contentView] frame];
CALayer *newWinLayer = [CALayer layer];
newWinLayer.frame = NSRectToCGRect(contentFrame);

换行，也是一个内存管理问题:

// NOTE: remember that the following 2 *Create* methods return
//  results that need to be released, unless you're using Garbage-Collection
// Also, I'm guessing that `layer` is created somewhere?
CALayer *layer = [CALayer layer];
CGColorRef backgroundCol = CGColorCreateGenericGray(0.0f, 0.5f);
CGColorRef borderCol = CGColorCreateGenericGray(0.756f, 0.5f);

layer.backgroundColor=backgroundCol;
layer.borderColor=borderCol;
CGColorRelease(backgroundCol); CGColorRelease(borderCol);
layer.borderWidth=5.0;

    // Calculate random origin point
rect.origin = SSRandomPointForSizeWithinRect( rect.size, [window frame] );

    // Set the layer frame to our random rectangle.
layer.frame = NSRectToCGRect(rect);
layer.cornerRadius = 25.0f;

[newWinLayer addSublayer:layer];

NSView *view = [newWin contentView];

// the order of the following 2 methods is critical:

[view setLayer:newWinLayer];
[view setWantsLayer:YES];

请参阅 NSView 的文档 setWantsLayer:

Discussion The order that setWantsLayer: and setLayer: are called is important, it makes the distinction between a layer-backed view, and a layer-hosting view.

A layer-backed view is a view that is backed by a Core Animation layer. Any drawing done by the view is the cached in the backing layer. You configured a layer-backed view by simply invoking setWantsLayer: with a value of YES. The view class will automatically create the a backing layer for you, and you use the view class’s drawing mechanisms. When using layer-backed views you should never interact directly with the layer.

A layer-hosting view is a view that contains a Core Animation layer that you intend to manipulate directly. You create a layer-hosting view by instantiating an instance of a Core Animation layer class and setting that layer using the view’s setLayer: method. After doing so, you then invoke setWantsLayer: with a value of YES. When using a layer-hosting view you should not rely on the view for drawing, nor should you add subviews to the layer-hosting view.

我相信您这样做的方式是尝试创建一个图层支持的 View ，您不应该像以前那样尝试与 View 的底层进行交互。您想要的是层托管的多样性。