Objective c 为什么outlineView会多次调用objectValueForTableColumn?
我正在学习Apple OS x开发者库提供的cocoa大纲视图。示例源如下所示:Objective c 为什么outlineView会多次调用objectValueForTableColumn?,objective-c,cocoa,Objective C,Cocoa,我正在学习Apple OS x开发者库提供的cocoa大纲视图。示例源如下所示: - (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item { return (item == nil) ? [FileSystemItem rootItem] : [(FileSystemItem *)item childAtIndex:index]; } - (BOOL)outl
- (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item {
return (item == nil) ? [FileSystemItem rootItem] : [(FileSystemItem *)item childAtIndex:index];
}
- (BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item {
return (item == nil) ? YES : ([item numberOfChildren] != -1);
}
- (NSInteger)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item {
return (item == nil) ? 1 : [item numberOfChildren];
}
- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item {
return (item == nil) ? @"/" : [item relativePath];
}
这将像一棵树一样列出我系统中的所有文件。
问题是:1.如果“/”下有32个文件,则该方法
- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item
- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item
将被呼叫62次,我不知道为什么?2.方法
- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item
- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item
没有关于行的参数,那么cocoa如何确定项目应显示的行
- (id)outlineView:(NSOutlineView*)outlineView objectValueForTableColumn:(NSTableColumn*)tableColumn byItem:(id)item
项是指向用于填充表的对象的指针。这就是NSOutlineViewDataSource协议
需要知道的全部内容。NSOutlineView内部显示行的详细信息