I have a pretty basic application in Jetpack Compose, where:
First screen has a lazyColumn with many items
Users can click on an item and be moved to a screen with details about the clicked item
Each item is modeled using a data class that is serializable
I've tried passing in the model class with the navigation using:
val modelDataAsString = Json.encodeToString(MODEL_CLASS.serializer(), modelData)
navController.currentBackStackEntry?.arguments?.putString("KEY", modelDataAsString)
navController.navigate("ROUTE/${modelDataAsString}")
But when I do this, I get the following exception:
java.lang.IllegalArgumentException: Navigation destination that matches request NavDeepLinkRequest{ uri=android-app://androidx.navigation/... cannot be found in the navigation graph NavGraph(0x0) startDestination={Destination(0x78da56c6) route=main}
Now, I understood that this is because my Model class in String form is way too long (relevant SO question).
So, searching SO, I found that the solution provided was using a SharedViewModel.
I have done this and everything works well, but something doesn't feel right passing around the viewModel.
What I want to know (and understand) if this is the proper way of
solving this issue. I am not looking for an opinion or a
recommendation, but a definitive answer.
At the bottom line, what I want to achieve is the ability to allow the onClick method on an item in my LazyColumn move the user to a screen of the item clicked.
Related
I am using react-native, nested react-navigation, SectionLists, ActionSheet, etc and I am having hard times setting up a decent way of refreshing components / screens. As I have a few different cases, I have also tried different approaches with no luck.
Examples:
- Sending a callback function as a param in the navigator when transitioning from one screen to another for state change.
- Assigning AsyncStorage.getItem straight to a state variable (e.g: used on a ListView) and expect it to refresh.
I've seen many questions in the react-navigation git repo (mainly on how to refresh a screen), and recent suggestion to the project on the best approach for future releases, that got me asking if this is something that is in place already.
I can say though, that I've successfully used redux to check the connection state (NetInfo), that although I couldn't yet port the same idea to a different schenario, I think that it is my best approach.
At the moment I have one schenario, that if solved, I believe will answer a few questions I have. For example:
I have a list of news in my Home screen and a few options in my Drawer navigator that I would like to, when clicked, to sort the Home list, without having to call navigate('screen_name') as I would like to, to still keep the Drawer opened after clicked.
What would be the best approach for this ?
Thanks in advance!
One approach you could follow is:
On click on a DrawerNavigator item, you can dispatch an action which would intern change the state by a value. Eg: filterBy: . This store value can be passed as a prop to your home screen, which would intern contain a logic to filter based on that value.
I havent worked with DrawerNavigator but i feel onPress on each item in drawer navigation can be prevented and a action can be invoked at the same place.
I've got a dijit Tree which is populated via a store wrapped in Observable, essentially the example here: http://dojotoolkit.org/reference-guide/1.10/dijit/Tree.html#id7 (Not that the example actually runs from the dojo site though: unless that's just my browser).
It's working well and I can expand and collapse items. However, it displays an expand icon even for the last item in a hierarchy - i.e. an item that doesn't have any children. When you try and expand such an item, it seems to realise this and the expand icon then disappears.
Does anyone know of how to supress the expand icons from appearing in the first place?
Thanks!
Implement the mayHaveChildren() method of the model:
Implementing logic here avoids showing +/- expando icon for nodes that
we know don't have children. (For efficiency reasons we may not want
to check if an element actually has children until user clicks the
expando node)
This method inputs one of your items and outputs true if it can be expanded; false otherwise.
Fairly new to developing for Windows 8, I'm working on an app that has a rather flat model. I have looked and looked, but can't seem to find a clear answer on how to set a WinJS page to prevent backward navigation. I have tried digging into the API, but it doesn't say anything on the matter.
The code I'm attempting to use is
WinJS.Navigation.canGoBack = false;
No luck, it keeps complaining about the property being read only, however, there are no setter methods to change it.
Thanks ahead of time,
~Sean
canGoBack does only have a getter (defined in base.js), and it reflects the absence or presence of the backstack; namely nav.history.backstack.
The appearance of the button itself is controlled by the disabled attribute on the associated button DOM object, which in turn is part of a CSS selector controlling visibility. So if you do tinker with the display of the Back button yourself be aware that the navigation plumbing is doing the same.
Setting the backstack explicitly is possible; there's a sample the Navigation and Navigation History Sample that includes restoring a history as well as preventing navigation using beforenavigate, with the following code:
// in ready
WinJS.Navigation.addEventListener("beforenavigate", this.beforenavigate);
//
beforenavigate: function (eventObject) {
// This function gives you a chance to veto navigation. This demonstrates that capability
if (this.shouldPreventNavigation) {
WinJS.log && WinJS.log("Navigation to " + eventObject.detail.location + " was prevented", "sample", "status");
eventObject.preventDefault();
}
},
You can't change canGoBack, but you can disable the button to hide it and free the history stack.
// disabling and hiding backbutton
document.querySelector(".win-backbutton").disabled = true;
// freeing navigation stack
WinJS.Navigation.history.backStack = [];
This will prevent going backward and still allow going forward.
So lots of searching and attempting different methods of disabling the Back Button, finally found a decent solution. It has been adapted from another stackoverflow question.
Original algorithm: How to Get Element By Class in JavaScript?
MY SOLUTION
At the beginning of a fragment page, right as the page definition starts declaring the ready: function, I used an adapted version of the above algorithm and used the resulting element selection to set the disabled attribute.
// Retrieve Generated Back Button
var elems = document.getElementsByTagName('*'), i;
for (i in elems)
{
if((" "+elems[i].className+" ").indexOf("win-backbutton") > -1)
{
var d = elems[i];
}
}
// Disable the back button
d.setAttribute("disabled", "disabled");
The code gets all elements from the page's DOM and filters it for the generated back button. When the proper element is found, it is assigned to a variable and from there we can set the disabled property.
I couldn't find a lot of documentation on working around the default navigation in a WinJS Navigation app, so here are some methods that failed (for reference purposes):
Getting the element by class and setting | May have failed from doing it wrong, as I have little experience with HTML and javascript.
Using the above method, but setting the attribute within the for loop breaks the app and causes it to freeze for unknown reasons.
Setting the attribute in the default.js before the navigation is finished. | The javascript calls would fail to recognize either methods called or DOM elements, presumably due to initialization state of the page.
There were a few others, but I think there must be a better way to go about retrieving the element after a page loads. If anyone can enlighten me, I would be most grateful.
~Sean R.
So I'm trying to wrap my head around MVVM and I'm finding that I have more questions than answers. The tutorials don't go far enough for me when it comes to the next step...
Basically I want a list of items and then a way to get the detail of each item.
Below is the examples that I've found online and they work great for displaying the list, but I need to know how I can use my VM to get the detail of this item.
private IList<item> m_items;
private IList<item> m_Item;
private IList<item> getItemDetail(Int32 iId)
{
var myItem =
from i in items
where i.iId == iId
select i;
m_Item = new List<item>();
foreach (var item in myItem)
{
m_Item.Add(item);
}
return m_Item;
}
public myViewModel()
{
m_items = new List<item>
{
new item(1, "test,),
new item(2, "test2"),
new item(3, "test1")
};
m_Item = new List<item>();
m_Item = getItemDetail(iId);
}
Update:
I updated my View Model code above. I think what I've done is I have added another List where when the user navigates to a detail page the view model gets called with the specific ID which then populates the detail List. I probably don't need a list here but I wanted to try to keep it consistent with the main page code.
In my detail page I'm setting up the VM this way:
itemViewModel VM = new itemViewModel((Int32)navigationParameter);
DataContext = VM;
When I break on the VM variable I see my 2 lists. However, my binding doesn't work on the XAML. If I need to post some sample XAML let me know. I can do that but I'm hoping there is something I'm missing here.
I'm trying to learn MVVM and I want to do things right. So instead of continuing down a wrong path I would really like to know the "right" way of doing things. So if you see errors, please let me know.
Thanks!
right, i'd suggest you go back to basics first and watch Laurent's Mix sessions about MVVM, you find links to then from the mvvmlight site on codeplex.
but to break it down you've hit a few of the hurdles I did when I first started.
1: (the biggest gotcha) for databinding to work, you must expose data using a property (get and set pattern), just a list variable won't work. this goes for everything you want to bind to. The alternative is to set item sources directly in code but you will loose all the features of databinding, including updates.
2: to understand databinding you need to understand the INotifyProperty changed pattern, this is the underlying gubbins (technical term ;-D) to enable binding to work properly. as suggested start a new "master/details" project template and walk through it, from the viewmodels holding the data to the views (pages) looking at the data in the view model
3: use observablecollections for lists, they are just better for binding and are basically just lists with extras
4: remember you can also bind the "selecteditem" or "selectedindex" of a listbox to capture what the user has selected, just be sure to set the binding to "twoway" so the view can push data to the viewmodel and not just read, like this: {binding myselecteditem, mode="twoway"}
hope this helps but if your still stuck Laurents videos are the best, just watch them a few times and follow what he does line by line
I believe you want to use what Microsoft calls the "master-detail binding scenario", where several controls bind to a single collection or to its selected item. To do so, you need to bind to a so called collection view, which is just a layer on top of the collection used by WPF. For instance, you can bind a ListBox's ItemSource and a ContentControl's Content to the same collection view, and the ContentControl will display the details of the the ListBox's selected item.
see: http://msdn.microsoft.com/en-us/library/ms752347.aspx#master_detail_scenario
P.S. you may want to use an ObservableCollection instead of a List, and make sure your view model implements INotifyPropertyChanged.
I want to navigate from a login screen to the dashboard in my Silverlight OOB app.
I started using Caliburn.Micro but now I'm having doubts seeing as all I can use is the Conductor. Or am I missing something?
Note: I changed constructor to Conductor as originally intended. This is what you get for not proofreading your questions.
There are several ways you could display a login screen, probably the nicest is to initiate it from your ShellViewModel. So, your ShellViewModel would have a dependency on your LoginViewModel, which you could inject as an abstraction (ILoginViewModel), or better still use an abstract factory instead, and inject that into your ShellViewModel constructor.
Either way, once you have an instance of your LoginViewModel in the ShellViewModel, you can display it either as a modal dialog box (in which case use the Caliburn.Micro WindowManager.ShowDialog method - inject this dependency as an IWindowManager abstraction), or display the login view as part of your shell views main content area, in which case your ShellViewModel would be a conductor, and will activate an instance of your LoginViewModel with the ActivateItem method.
Once you have received input from your LoginViewModel, either as a modal dialog or conducted view, you can display your DashboardViewModel as appropriate using the ShellViewModel as a conductor.