Question

我发现当我将NSView（viewA aleardy添加到superView中）重新分配给另一个视图（new viewB）时，如下所示：

Method originalMethod = class_getInstanceMethod([NSArray class], @selector(objectAtIndexedSubscript:));
Method swapMethod = class_getInstanceMethod([NSArray class], @selector(objectAtIndexedSubscriptNew:));
method_exchangeImplementations(originalMethod, swapMethod);

viewB不会更新到superView，事件我尝试以下方法：

1）

viewA = [[NSView alloc] init];
viewB = [[NSView alloc] init];
[self.view addSubview viewA];
viewA = viewB;

2） [viewA setHidden: YES]; [viewA setHidded: NO];

只有删除viewA并将其重新添加回它的超级视图才能正常工作：

[viewA setNeedLayout: YES];

有人可以帮忙解释为什么方法1）和2）无法更新viewA的矩形吗？

Answer 1

如果要查看视图层次结构，则必须将视图添加到视图层次结构中。 viewA = viewB;使变量viewA指向与viewB相同的视图，它不会将viewB添加到视图层次结构中。

以下是您的代码所做的事情：

viewA = [[NSView alloc] init]; // viewA points to a new view(A)
viewB = [[NSView alloc] init]; // viewB points to a new view(B)
[self.view addSubview viewA]; // view(A) is added to the view hierarchy and will be displayed
viewA = viewB; // variable viewA points to view(B)

[viewA setHidden: YES]; // hides view(B)
[viewA setHidded: NO]; // unhides view(B), but view(B) isn't visible because it isn't part of the view hierarchy

[viewA setNeedLayout: YES]; // doesn't do anything, view(B) isn't visible because it isn't part of the view hierarchy

[viewA removeFromSuperView]; // doesn't do anything, view(B) isn't in a superview
[self.view addSubview:viewA]; // view(B) is added to the view hierarchy and will be displayed

解决方案：将视图（B）添加到视图层次结构

viewA = [[NSView alloc] init]; // viewA points to a new view(A)
viewB = [[NSView alloc] init]; // viewB points to a new view(B)
[self.view addSubview viewA]; // view(A) is added to the view hierarchy and will be displayed
[self.view addSubview viewB]; // view(B) is added to the view hierarchy and will be displayed

为什么需要删除/添加NSView后重新分配以显示它

1 个答案: