重写此方法，来控制 UIMenuItem 的显示和隐藏：
- (BOOL)canPerformAction:(SEL)action withSender:(id)sender
{
if (action == @selector(copy:))
{
return YES;
}
else if (action == @selector(select:))
{
return YES;
}
else if (action == @selector(selectAll:))
{
return YES;
}
return [super canPerformAction:action withSender:sender];
}
以下是系统默认的 UIMenuItem 所对应的 action：
-
cut:// 剪切 -
copy:// 拷贝 -
select:// 选择 -
selectAll:// 全选 -
paste:// 粘贴 -
delete:// 删除 -
_promptForReplace:// Replace... -
_transliterateChinese:// 简<=>繁 -
_showTextStyleOptions:// B/<u>U</u> -
_define:// Define -
_addShortcut:// Learn... -
_accessibilitySpeak:// Speak -
_accessibilitySpeakLanguageSelection:// Speak... -
_accessibilityPauseSpeaking:// Pause -
_share:// 共享... -
makeTextWritingDirectionRightToLeft:// 往右缩进 -
makeTextWritingDirectionLeftToRight:// 往左缩进
