为什么NSAnimationContext completionHandler不工作(有时)？

Question

    // wc here is an NSWindowController

    [NSAnimationContext beginGrouping];
    [[NSAnimationContext currentContext] setDuration:0.5f];

    if (duplication) {
        NSPoint origin = initialSize.origin;
        origin.y += initialSize.size.height;
        origin = [wc.window cascadeTopLeftFromPoint:origin];
        origin.y -= initialSize.size.height;
        //[[wc.window animator] setFrameOrigin:origin];   // Why setFrameOrigin and cascadeTopLeftFromPoint are not animated?
        initialSize.origin = origin;
        [[wc.window animator] setFrame:initialSize display:YES];
    }

    // This block should be invoked when all of the animations started above have completed or been cancelled.
    // For not to show the edit window till the duplication animation not finished
    [NSAnimationContext currentContext].completionHandler = ^{
        if (edit)
            [wc editDocument:self];
        else
            if (fullScreen)
                [wc.window toggleFullScreen:self];
    };

    [NSAnimationContext endGrouping];

在这种情况下，完成块被执行，但不幸的是，它不等待窗口重新定位完成，而是立即打开窗口的编辑工作表，并将它们一起移动。

最奇怪的是，在同一个源文件中，上面几行相同类型的补全块工作得很好:-O

这里我漏掉了什么？

Answer 1

这实际上不是一个bug，但它已经让我被绊倒了很多次。您必须在调用任何动画的之前设置完成处理程序。

Answer 2

查看completionHandler的文档

如果设置为非nil值，则只要完成或取消了随后添加到当前NSAnimationContext分组的所有动画，就可以保证在主线程上调用上下文的。

来源：https://developer.apple.com/documentation/appkit/nsanimationcontext/1531132-completionhandler?language=objc

完成处理程序只影响在设置完成处理程序之后添加的动画。

最后还说：

如果在当前分组结束之前没有添加动画，或者completionHandler被设置为不同的值，则

将立即调用处理程序。

在您的示例中，在设置完成处理程序和当前分组的末尾之间没有添加动画，因此您的完成处理程序会立即被调用。

正确的代码应该是：

// wc here is an NSWindowController

[NSAnimationContext beginGrouping];
[[NSAnimationContext currentContext] setDuration:0.5f];

// This block should be invoked when all of the animations started above have completed or been cancelled.
// For not to show the edit window till the duplication animation not finished
[NSAnimationContext currentContext].completionHandler = ^{
    if (edit)
        [wc editDocument:self];
    else
        if (fullScreen)
            [wc.window toggleFullScreen:self];
};

if (duplication) {
    NSPoint origin = initialSize.origin;
    origin.y += initialSize.size.height;
    origin = [wc.window cascadeTopLeftFromPoint:origin];
    origin.y -= initialSize.size.height;
    //[[wc.window animator] setFrameOrigin:origin];   // Why setFrameOrigin and cascadeTopLeftFromPoint are not animated?
    initialSize.origin = origin;
    [[wc.window animator] setFrame:initialSize display:YES];
}

[NSAnimationContext endGrouping];

Answer 3

好的，这是一个BUG，我提交了一份bug报告。下一个版本可以完美地工作

__block NSRect newPosition(initialSize);
[NSAnimationContext runAnimationGroup:^(NSAnimationContext *context){
    [context setDuration:0.5f];

    if (duplication) {
        NSPoint origin = newPosition.origin;
        origin.y += newPosition.size.height;
        origin = [wc.window cascadeTopLeftFromPoint:origin];
        origin.y -= newPosition.size.height;
        //[[wc.window animator] setFrameOrigin:origin];   // Why setFrameOrigin and cascadeTopLeftFromPoint are not animated?
        newPosition.origin = origin;
        [[wc.window animator] setFrame:newPosition display:YES];
    }
} completionHandler:^{
    // This block will be invoked when all of the animations
    // started above have completed or been cancelled.
    if (edit)
        [wc editDocument:self];
    else
        if (fullScreen)
            [wc.window toggleFullScreen:self];
}];