Caching Android Fragment ViewModel_course

<div><h2>&#x1f4ac; Questions and Help</h2> <p>Hi all,</p> <p>I have a quick question regarding caching of view models. </p> <p>I have an activity which is using a BottomNavigationView in order to display 4 different fragments. The Activity itself, has the following attributes: <br /></p> <pre><code> [MvxActivityPresentation] [Activity(Label &#61; &#34;Device&#34;, ScreenOrientation &#61; ScreenOrientation.Portrait, LaunchMode &#61; LaunchMode.SingleTop, Theme &#61; &#34;/AppTheme&#34;)] </code></pre> <p>And every fragment in my activity has the following attributes: <br /></p> <pre><code> [MvxFragmentPresentation(typeof(DeviceViewModel), Resource.Id.content_frame, true, IsCacheableFragment &#61; true)] </code></pre> <p>where &#34;content_frame&#34; is the id of the activity&#39;s frame holding the fragments.</p> <p>I&#39;m wondering if I can get some guidance vis-a-vis to the caching of the fragment view models. Some of these view models could potentially be doing some expensive work on </p><pre><code>Initialize</code></pre>, and I want to get to a point where if a fragment has already been opened, it will just load its state from a cache rather than recreating the view model every time. <br /> <p>Currently, I have an even listener registered on the BottomNavigationView to handle every item click, and based of the id, navigate to given view model like so: <br /></p> <pre><code> private void BottomNavigation_NavigationItemSelect(object sender, BottomNavigationView.NavigationItemSelectedEventArgs e) { ToggleNavItem(e.Item.ItemId); } private void ToggleNavItem(int selectedItemId) { switch(selectedItemId) { case Resource.Id.device_menu_overview: { ViewModel.ShowDefaultViewModelCommand.Execute(null); break; } case Resource.Id.device_menu_functions: { ViewModel.ShowDeviceFunctionsCommandAsync.Execute(null); break; } case Resource.Id.device_menu_variables: { ViewModel.ShowDeviceVariablesCommandAsync.Execute(null); break; } case Resource.Id.device_menu_events: { ViewModel.ShowDeviceEventsCommandAsync.Execute(null); break; } default: return; } } </code></pre> <p>The matching commands for this switch statement are initialised in the view model constructor like so: <br /></p> <pre><code> ShowDefaultViewModelCommand &#61; new MvxAsyncCommand(async () &#61;&gt; await _navigationService.Navigate&lt;deviceoverviewviewmodel&gt;()); ShowDeviceFunctionsCommandAsync &#61; new MvxAsyncCommand(async () &#61;&gt; await _navigationService.Navigate&lt;devicefunctionsviewmodel&gt;()); ShowDeviceVariablesCommandAsync &#61; new MvxAsyncCommand(async () &#61;&gt; await _navigationService.Navigate&lt;devicevariablesviewmodel&gt;()); ShowDeviceEventsCommandAsync &#61; new MvxAsyncCommand(async () &#61;&gt; await _navigationService.Navigate&lt;deviceeventsviewmodel&gt;()); &lt;/deviceeventsviewmodel&gt;&lt;/devicevariablesviewmodel&gt;&lt;/devicefunctionsviewmodel&gt;&lt;/deviceoverviewviewmodel&gt;</code></pre> <p>I&#39;m aware that the navigation service also allows you to pass in a view model instance into the navigate method, rather than the method above, but I am unsure how MvvmCross caches view models internally, and if not, how I can go about creating my own cache for this situation.</p> <p>Let me know if I can provide any more detail to help on this one, I very much appreciate the help Liam</p><p>该提问来源于开源项目&#xff1a;MvvmCross/MvvmCross</p></div>

Android Fragment底部选项卡，如何能在跳转二级、三级甚至更多层页面时也保持活动状态_course

Android Fragment底部选项卡，如何能在跳转二级、三级甚至更多层页面时也保持活动状态，如题：项目中要用到，在Fragment多层子界面依然可以进行Fragment之间的传递，如： A Fragment > A按钮 > A界面 > A按钮 > C Fragment > C界面，当点击返回时，返回A界面（从A界面进入C界面时，如从C Fragment进入则返回C Fragmeent） Ps： 当从A界面 > C Fragment时，底部选项卡的显示也要进行相关切换...... 上述就是需求了，之前Fragment子界面是在布局中直接引用自定义View来实现底部选项卡不被覆盖的，但这样并不好，因为它没有自己的生命周期导致扩展不行，想把Fragment子界面换成有自己生命周期的，但无从下手，请大牛们指点下，感激......