I‘m a beginer who uses MvvmCross for the Xamarin.Android.I try to realize the function like 'click the button and show a dialog to say hello'.
When I use the way which sets ViewModel object to Activity object's DataContext to bind,I can pass UI object directly (or using Interface indirectly).In this way,I can access UI object to show a dialog.
In another way likes the offical demo, bing the UI object and ViewModel automatically,how can I show the dialog?The auto bing code like this
public class App:MvxApplication { public App() { Mvx.RegisterSingleton(new MvxAppStart()); } }
[Activity(Label = "MvvmC_TutorialActivity")] public class MvvmC_TutorialActivity : MvxActivity
{
.............
}
Thanks！
I slove the problem!I can pass the UI object in 'MvxActivity's OnViewModelSet'.
protected override void OnViewModelSet()
{
SetContentView(Resource.Layout.View_Tip);//pass UI object here
}
Related
Split out from Vaadin Dataprovider: how to avoid "auto-fetch"?.
Given a Vaadin Flow 19 app with a MainView extends AppLayout, a GridView and an EmptyView And #PreserveOnRefresh annotation is used on MainView.
When returning to GridView, the GridView should be exactly in the same state as before:
open GridView using button in MainView for the first time -> Grid uses DataProvider to fetch data from backend
enter "Spiderman" in TextField with caption "stateCheck"
switch to EmptyView using button in MainView
in the real app: do something in EmptyView and potentially other views
return to GridView using button in MainView for the 2nd time
Then (1) the TextField with caption "stateCheck" should display the value "Spiderman"
And (2) the grid should still show the same data as before; it should not reload the data from the backend
Observed behaviour:
(1) is ok, but (2) not: the grid always calls fetch method to get data from the backend.
How do I achieve the desired behavior?
Here's the code of my GridView which also fakes the backend DataProvider:
#Route(value = "grid", layout = MainView.class)
public class GridView extends VerticalLayout {
public GridView() {
final Grid<Person> g = new Grid(Person.class);
g.setColumns("name");
g.setDataProvider(DataProvider.fromCallbacks(q -> fetch(q), q -> count(q)));
add(g);
add(new TextField("State check"));
}
// fake DataProvider
private int count(Query<Person, Void> q) { return 3; }
private Stream<Person> fetch(Query<Person, Void> q) {
q.getLimit(); //vaadin checks these have been called
q.getOffset(); //vaadin checks these have been called
System.out.println("fetching again");
return Arrays.asList(new Person("1"), new Person("2"), new Person("3")).stream();
}
}
MainView is used to switch between GridView and EmptyView
#PreserveOnRefresh
public class MainView extends AppLayout {
private Component emptyBView;
private Component gridBView;
public MainView() {
final Button emptyB = new Button("Btn empty");
emptyB.addClickListener(e -> {
if (emptyBView == null) { emptyBView = new EmptyView();}
setContent(emptyBView);
});
addToNavbar(emptyB);
final Button gridB = new Button("Btn grid");
gridB.addClickListener(e -> {
if (gridBView == null) gridBView = new GridView();
setContent(gridBView);
});
addToNavbar(gridB);
}
}
This is actually intentional behavior. The server side dataprovider listener needs to be removed when component is detached and rewired on attaching. The reason is that otherwise there would be listeners accumulating and producing a memory leakage. If you think your users would be using refresh page often, you should consider adding a cache to your application to optimize performance.
Now one could entertain with the idea of having this kind of caching of previous loaded data behavior via API in Grid also in Vaadin framework, as it may or may not be desirable. It is application specific.
If the use case of refreshing is really to get the fresh data of live and active database, it is actually desired that data is loaded when page is refreshed.
If the desire is to avoid extra bombarding of DB as data is known to be static, you want to have caching.
Using Vaadin 14.0.13 without compatibility mode.
I use a view to create a Dialog with dynamic content:
#Route("")
public class MainView extends VerticalLayout {
public MainView(DialogContentProvider contentProvider) {
this.add(new Button("Click me!", event -> new Dialog(contentProvider.create()).open()));
}
}
The contentProvider is an interface
public interface DialogContentProvider {
Component create();
}
with this implementation:
public class CheckBoxContentProvider implements DialogContentProvider {
#Override
public Component create() {
return new Checkbox("My checkbox", true);
}
}
instantiated by Spring Boot (version 2.2.1.RELEASE) with a bean:
#Bean
public DialogContentProvider contentProvier() {
return new CheckBoxContentProvider();
}
When I click on the button, the dialog is opened but the checkbox haven't the box:
The source code is on github: https://github.com/gronono/bug-vaadin-checkbox
I don't understand why and how I can fix it. If I include the checkbox creation inside the main view, it works fine:
#Route("")
public class MainView extends VerticalLayout {
public MainView(DialogContentProvider contentProvider) {
// this.add(new Button("Click me!", event -> new Dialog(contentProvider.create()).open()));
this.add(new Button("Click me!", event -> new Dialog(new Checkbox("My checkbox", true)).open()));
}
}
This sound an awful lot like this (related github issue)
Basically, this happens when you don't have any View that uses a Checkbox directly, but through other means like reflection or in your case the contentProvider, because in no view of your app there is any import statement of Checkbox (--> therefore, vaadins scan during the installation will not detect usages of Checkbox, so it will not download npm stuff for checkbox).
in the github it says this will be fixed in 14.1
If you need a fix now, for me it worked when I declared a field of that type in any view with a #Route. That field doesn't have to be used.
#Route("")
public class MainView extends VerticalLayout {
private Checkbox unusedCheckbox; // this line fixes it.
public MainView(DialogContentProvider contentProvider) {
this.add(new Button("Click me!", event -> new Dialog(contentProvider.create()).open()));
}
}
Addendum: This is not related to the Checkbox component specifically, it happens with any vaadin component that isn't initially scanned in a route, but used anyway through reflective-, provider-, or generic means.
Edit: You can also work around this currently by adding a #Route(registerAtStartup = false) to your provider that uses the Checkbox directly. This will make vaadins scan see the checkbox usage (therefore importing its npm package), but will not actually register the provider as a real route..
Another way which I prefer if you need this for multiple components is to create a new View with a #Route(registerAtStartup = false) which only defines private variables for each component that you'll need in the application (and arent already used directly in some view of yours). This has the advantage of all these component usage definitions in one place, and once the official fix is released, you need only to delete one class and the deprecated workaround is gone.
#Route(registerAtStartup = false)
public class ComponentImportView extends VerticalLayout {
private Checkbox checkBox;
private Upload upload;
private ProgressBar progressBar;
}
I have a Vaadin Navigator with multiple View elements. Each view has a different purpose however some also contain common traits that I have put inside custom components.
One of those custom components is the menu - it is positioned at the top and allows navigation between the different views. I create and add this component inside the constructor of each view (if you are interested in the menu's implementation see the end of this post). Here is a skeleton for each custom view:
class MyViewX implements View {
MenuViewComponent mvc;
public MyViewX() {
mvc = new MenuViewComponent();
addComponent(mvc);
}
#Override
public void enter(ViewChangeEvent event) {
}
}
So far, so good. In order to make things simple I will explain my problem using a simple label and not one of my other custom components but the dependency that I will describe here is the same for those components just like with the label.
Let's say I have a label which sole purpose is to display a greeting with the user's username. In order to do that I use VaadinSession where I store the attribute. This is done by my LoginController, which validates the user by looking into a database and if the user is present, the attribute is set and one of the views is opened automatically. The problem is that VaadinSession.getCurrent().getAttribute("username") returns null when called inside the constructor. This of course makes sense omho because a constructor should not be bound by a session-attribute.
So far I have managed to use the enter() method where there is no problem in retrieving session attributes:
class MyViewX implements View {
MenuViewComponent mvc;
public MyViewX() {
mvc = new MenuViewComponent();
addComponent(mvc);
}
#Override
public void enter(ViewChangeEvent event) {
String username = (String)VaadinSession.getCurrent().getAttribute("username");
Label greeting = new Label("Hello " + username);
addComponent(greeting);
}
}
The issue that comes from this is obvious - whenever I open the view where this label is present, a new label is added so if I re-visit the view 10 times, I will get 10 labels. Even if I move the label to be a class member variable the addComponent(...) is the one that screws things up. Some of my custom components really depend on the username attribute (in order to display user-specific content) hence I also have to place those in the enter(...) method. The addComponent(...) makes a mess out of it. I even tried the dirty way of removing a component and then re-adding it alas! in vain:
class MyViewX implements View {
MenuViewComponent mvc;
Label greeting;
public MyViewX() {
mvc = new MenuViewComponent();
addComponent(mvc);
}
#Override
public void enter(ViewChangeEvent event) {
String username = (String)VaadinSession.getCurrent().getAttribute("username");
greeting = new Label("Hello " + username);
// Remove if present
try { removeComponent(greeting); }
catch(Exception ex) { }
// Add again but with new content
addComponent(greeting);
}
}
but it's still not working. So my question is: what is the simplest way of updating a component that requires session-bound attributes?
The navigation via the menu custom component is omho not the issue here since all components of the menu are loaded in it's constructor. That's why it's also load that component in particular in a view's own constructor. Here is an example of a button in my menu that opens a view:
#SuppressWarnings("serial")
#PreserveOnRefresh
public class MenuViewComponent extends CustomComponent {
public MenuViewComponent(boolean adminMode) {
HorizontalLayout layout = new HorizontalLayout();
Label title = new Label("<h2><b>Vaadin Research Project</b></h2>");
title.setContentMode(ContentMode.HTML);
layout.addComponent(title);
layout.setComponentAlignment(title, Alignment.TOP_LEFT);
Button personalDashboardButton = new Button("Personal dashboard", new Button.ClickListener() {
#Override
public void buttonClick(ClickEvent event) {
getUI().getNavigator().navigateTo(MainController.PERSONALDASHBOARDVIEW);
}
});
personalDashboardButton.setStyleName(BaseTheme.BUTTON_LINK);
layout.addComponent(personalDashboardButton);
layout.setComponentAlignment(personalDashboardButton, Alignment.TOP_CENTER);
// Add other buttons for other views
layout.setSizeUndefined();
layout.setSpacing(true);
setSizeUndefined();
setCompositionRoot(layout);
}
}
PERSONALDASHBOARDVIEW is just one of the many views I have.
It may be worth considering how long should your view instances "live", just as long they're displayed, until the session ends or a mix of the two. With this in mind and depending on what needs to happen when you enter/re-enter a view, you have at least the following 3 options:
1) Recreate the whole view (allowing for early view garbage-collection)
first register a ClassBasedViewProvider (instead of a StaticViewProvider) which does not hold references to the created views:
navigator = new Navigator(this, viewDisplay);
navigator.addProvider(new Navigator.ClassBasedViewProvider(MyView.NAME, MyView.class));
simple view implementation
public class MyView extends VerticalLayout implements View {
public static final String NAME = "myViewName";
#Override
public void enter(ViewChangeListener.ViewChangeEvent event) {
// initialize tables, charts and all the other cool stuff
addComponent(new SweetComponentWithLotsOfStuff());
}
}
2) Keep some already created components and replace others
public class MyView extends VerticalLayout implements View {
private MySweetComponentWithLotsOfStuff mySweetComponentWithLotsOfStuff;
public MyView() {
// initialize only critical stuff here or things that don't change on enter
addComponent(new MyNavigationBar());
}
#Override
public void enter(ViewChangeListener.ViewChangeEvent event) {
// oh, so the user does indeed want to see stuff. great, let's do some cleanup first
removeComponent(mySweetComponentWithLotsOfStuff);
// initialize tables, charts and all the other cool stuff
mySweetComponentWithLotsOfStuff = new SweetComponentWithLotsOfStuff();
// show it
addComponent(mySweetComponentWithLotsOfStuff);
}
}
3) Lazy creating and updating (or not) the content when entering
public class MyView extends VerticalLayout implements View {
private boolean isFirstDisplay = true;
private MySweetComponentWithLotsOfStuff mySweetComponentWithLotsOfStuff;
public MyView() {
// initialize only critical stuff here, as the user may not even see this view
}
#Override
public void enter(ViewChangeListener.ViewChangeEvent event) {
// oh, so the user does indeed want to see stuff
if (isFirstDisplay) {
isFirstDisplay = false;
// lazily initialize tables, charts and all the other cool stuff
mySweetComponentWithLotsOfStuff = new SweetComponentWithLotsOfStuff();
addComponent(mySweetComponentWithLotsOfStuff);
} else {
// maybe trigger component updates, or simply don't do anything
mySweetComponentWithLotsOfStuff.updateWhateverIsRequired();
}
}
}
I'm sure (and curious) that there may be other options, but I've mainly used a variation of 1) using spring with prototype views and component tabs.
I have a view in the Views folder and I have a class library project. In this project I want to render view to string.
public class DumpService
{
public void Method()
{
var renderedView = SomeMethodForRenderingView();
}
}
I have found some answers, but there are used controller context which I don't have in the class library project.
How can I do this?
You need to read the view text - just open it with and read the text, and then parse it with :
Razor.Parse
I am am trying to create a tabbed view using the Cirrious Conference sample but seem to be having problems displaying my data. The problem arises when the view which hosts the tab is invoked specifically at the code below
// Initialize a TabSpec for each tab and add it to the TabHost
spec = TabHost.NewTabSpec("welcome");
spec.SetIndicator(this.GetText("Welcome"),Resources.GetDrawable(Resource.Drawable.Tab_Welcome));
spec.SetContent(CreateIntentFor(ViewModel.Welcome));
TabHost.AddTab(spec);
My ViewModel calss is below
public class WelcomeViewModel : MvxViewModel
{
private string _description;
public string Description
{
get
{
return _description;
}
set
{
_description = value;
FirePropertyChanged("Description");
}
}
public WelcomeViewModel(string description)
{
Description = description;
}
public WelcomeViewModel()
{
}
}
The ViewModel.Welcome object is created and initialised with the data passed to it and remains so until control passes the SetContent method but when AddTab is called the WelcomeViewModel constructor seems to be invoked again and the data is reset. The call stack traces this to the
base.OnCreate(bundle);
call in the BaseTabbedView class. How do I keep hold of the data in the WelcomeViewModel so that it is displayed in my tab, Many Thanks
I have a feeling this is probably a bug I fixed a couple of weeks ago.
The bug was that the cache used for storing these child viewmodels was starting its indexing at 0 - and 0 was also being treated as the empty value by the Android Intent.
In vnext, see this checkin https://github.com/slodge/MvvmCross/commit/bcebadffee3850857d6a73070704e72b3aa72bcb
In master, see https://github.com/slodge/MvvmCross/commit/c3171e27168bf2b7e48dd73d105f5a08870cec5a