之前从iOS开发转战这里的人小伙伴对NSTrackingArea类应该会有点陌生，毕竟手机开发中不需要监听鼠标的移动，这个类就是跟我们mac常用鼠标有关，我们简单了解一下我们常用的一些使用场景
mouseEntered和mouseExited
NSView要想响应鼠标进出事件，需要重写NSView的updateTrackingAreas方法，updateTrackingAreas 是View的大小发生改变的时候进行的回调，让我们在这个时机有机会重新去设置View的追踪区域NSTrackingArea，在设置NSTrackingArea的时候，可以决定要响应鼠标的哪些事件，看下面例子：
红色区域的是SuperView，蓝色区域的是SubView
#import "SuperView.h"
@implementation SuperView
- (void)drawRect:(NSRect)dirtyRect {
[super drawRect:dirtyRect];
// Drawing code here.
}
- (void)updateTrackingAreas {
NSArray * trackingAreas = [self trackingAreas];
for (NSTrackingArea *area in trackingAreas) {
[self removeTrackingArea:area];
}
NSTrackingArea *trackingArea = [[NSTrackingArea alloc] initWithRect:self.bounds
options:(NSTrackingMouseEnteredAndExited |
NSTrackingMouseMoved |
NSTrackingActiveInActiveApp |
NSTrackingInVisibleRect |
NSTrackingAssumeInside |
NSTrackingCursorUpdate)
owner:self
userInfo:nil];
[self addTrackingArea:trackingArea];
}
- (void)mouseEntered:(NSEvent *)event {
NSLog(@"MacLean SuperView mouseEntered");
}
- (void)mouseExited:(NSEvent *)event {
NSLog(@"MacLean SuperView mouseExited");
}
@end
- 代码中有个options的值有好多，除了移动和进出两个枚举以外，其它的这四位一定要加上，要不然方法不调用，具体的原因不多解释了应该能看懂枚举的意思哈
NSTrackingActiveInActiveApp |NSTrackingInVisibleRect |NSTrackingAssumeInside |NSTrackingCursorUpdate - 我们发现在子View中调用super，会让事件在响应链上传播，会让父View也响应到事件，也就是说，如果子View明确处理事件，就不应该调用super，在NSView（Handling Events in Your Subclass）的文档中对此进行了说明。
mouseDown和mouseUp
mouseDown和mouseUp事件是不需要在updateTrackingAreas中设置的，默认都能响应的，如果不想父View响应，那么只要不调用super，不让事件在响应链上传播就可以了。
- (void)mouseDown:(NSEvent *)event {
// [super mouseDown:event];
NSLog(@"MacLean SubView mouseDown");
}
- (void)mouseUp:(NSEvent *)event {
// [super mouseUp:event];
NSLog(@"MacLean SubView mouseUp");
}
//SuperView
- (void)mouseDown:(NSEvent *)event {
NSLog(@"MacLean SuperView mouseDown");
}
- (void)mouseUp:(NSEvent *)event {
NSLog(@"MacLean SuperView mouseUp");
}
SubView中调用了super，结果
2020-06-19 10:49:28.585185+0800 MacLearn[21625:3218490] MacLean SuperView mouseDown
2020-06-19 10:49:28.585257+0800 MacLearn[21625:3218490] MacLean SubView mouseDown
2020-06-19 10:49:28.708589+0800 MacLearn[21625:3218490] MacLean SuperView mouseUp
2020-06-19 10:49:28.708654+0800 MacLearn[21625:3218490] MacLean SubView mouseUp
2020-06-19 10:49:31.387772+0800 MacLearn[21625:3218490] MacLean SuperView mouseDown
2020-06-19 10:49:31.533055+0800 MacLearn[21625:3218490] MacLean SuperView mouseUp
- NSView的事件回调方法默认都是调用super，也就是说在子View上鼠标事件会通过响应链传递到父View的，如果，只想子View处理鼠标事件，需要重写NSView的事件回调方法，去掉super的调用。
mouseMoved
NSView要想响应mouseMoved事件是需要在updateTrackingAreas中设置的，我们看看下面的例子，鼠标从下滑到上
\\ SubView
- (void)mouseMoved:(NSEvent *)event {
NSLog(@"MacLean SubView mouseMoved");
}
\\SuperView
- (void)mouseMoved:(NSEvent *)event {
NSLog(@"MacLean SuperView mouseMoved");
}
2020-06-19 10:57:00.707662+0800 MacLearn[21716:3223044] MacLean SuperView mouseEntered
2020-06-19 10:57:00.808957+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:00.876397+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:00.887334+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:02.169826+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:02.181265+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:02.192857+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:02.203424+0800 MacLearn[21716:3223044] MacLean SubView mouseEntered
2020-06-19 10:57:02.203884+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:02.203943+0800 MacLearn[21716:3223044] MacLean SubView mouseMoved
2020-06-19 10:57:02.214461+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:02.214565+0800 MacLearn[21716:3223044] MacLean SubView mouseMoved
2020-06-19 10:57:06.309816+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:06.309949+0800 MacLearn[21716:3223044] MacLean SubView mouseMoved
2020-06-19 10:57:06.366530+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:06.366640+0800 MacLearn[21716:3223044] MacLean SubView mouseMoved
2020-06-19 10:57:08.773979+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:08.774084+0800 MacLearn[21716:3223044] MacLean SubView mouseMoved
2020-06-19 10:57:08.785382+0800 MacLearn[21716:3223044] MacLean SubView mouseExited
2020-06-19 10:57:08.786015+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:08.796243+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:08.807529+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:08.818352+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:08.829537+0800 MacLearn[21716:3223044] MacLean SuperView mouseMoved
2020-06-19 10:57:09.347431+0800 MacLearn[21716:3223044] MacLean SuperView mouseExited
发现没，我们在SubView中没有调用super，结果，在SubView中滑动的时候，SuperView居然也能响应move事件，具体原因不详。我们看看SubView中调用super会是什么表现呢？
2020-06-19 11:12:20.857676+0800 MacLearn[21842:3229852] MacLean SuperView mouseEntered
2020-06-19 11:12:20.858661+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:20.867886+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:20.884067+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:20.890665+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:21.070717+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:21.083426+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:21.093463+0800 MacLearn[21842:3229852] MacLean SubView mouseEntered
2020-06-19 11:12:21.094096+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:21.094205+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:21.094260+0800 MacLearn[21842:3229852] MacLean SubView mouseMoved
2020-06-19 11:12:21.104596+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:21.104705+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:21.104748+0800 MacLearn[21842:3229852] MacLean SubView mouseMoved
2020-06-19 11:12:21.115910+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
2020-06-19 11:12:21.116023+0800 MacLearn[21842:3229852] MacLean SuperView mouseMoved
move的表现还是很特殊的，在子View中移动，不管子View中有没有调用super，父View的move事件都会响应。
Tool Tip
toop tip是NSView提供的一个功能，运行hoverNSView的时候文案提示。
调用方法设置就可以了，很简单。可是在实际开发中遇到了问题，居然不起作用，最后发现是和NSTrackingArea有关系。NSView可能会有多个NSTackingArea，我们在设置鼠标事件的时候，不能无脑的把NSView的所有NSTackingArea都remove掉，只需要把我们设置的NSTackingArea remove掉就可以了
- (void)updateTrackingAreas
{
if (hovered) {
hovered = NO;
if (self.delegate && [self.delegate respondsToSelector:@selector(baseView:mouseExited:)]) {
[self.delegate baseView:self mouseExited:nil];
}
}
if (_trackingArea) {
[self removeTrackingArea:_trackingArea];
}
if (self.userInteraction && self.needTracking && !self.isHidden) {
_trackingArea = [[NSTrackingArea alloc] initWithRect:self.bounds options:(NSTrackingMouseEnteredAndExited |NSTrackingMouseMoved|NSTrackingActiveInActiveApp |NSTrackingInVisibleRect |NSTrackingAssumeInside |NSTrackingCursorUpdate) owner:self userInfo:nil];
[self addTrackingArea:_trackingArea];
}
}
- macOS开发相对比较小众开发人员不多，导致官方维护的也不好，使用起来各种难受，遇到问题资料也少。
电脑和手机开发有些不一样，最大的不同就是对事件的处理，在手机上是用手指操作的，只有点击动作（长按、双击），在电脑上是用鼠标操作的，除了点击动作还有鼠标hover的动作，和电视上有个selected状态类似，mouseEntered和mouseExited就是hover的两个回调。
需要说明的是，macOS的hover事件和click事件的传递和Android中事件传递是不一样的，我们看看在子view中点击断点看看：
看到没，是Application kit直接把事件分发到了子view上，没有经过父view，这个和Android是不一样的。
还有比较奇葩的是，在子View的mouseDown中把子View从父View上移除掉时，子View的mouseUp居然不会被回调了，而且会回调到父View的mouseUp上，如果父View的mouseUp中做了一些工作就会出错。mouseDown和mouseUp成对出现，能理解，毕竟实际动作就是这样的，可是系统居然不判断接收目标对不对，我觉得这应该是macOS的bug。
解决办法时，在mouseUp响应的时候，(转)看一下自身的mouseDown有没有响应过。
完结
