quite new to Formik and FieldArrays. Any help is much appreciated.
The problem:
I have a FieldArray which renders a list of objects each having some Fields, a deleteCurrentObject and a addNewObject button . I have successfully implemented the functionality of adding new object and deleting the current one. What I need to implement and still have not found a solution to this is a toggle switch for each of the nested objects inside this FieldArray that will change the state of each object in the parent FieldArray. To be more specific, I need to be able to disable one or more of the Fields (inputs) depending on the status of the toggler. For this reason I have included in the ionitialValues of the FieldArray an isEditing boolean property, with the hope of switching its state from true to false. I have managed to do this with the help of setFieldValue or directly but the problem with this approach is that once the isEditing value of each object inside the FieldArray is changing, the change is not propagated down.
In any case , any indication of how to implement a toggle switch inside each object of a FieldArray is deeply appreciated.
Related
Maybe my question is a nooby one, but i really try to understand how to implement the following operations:
How to add item for a list without the need of rebuilding all list.
How to update a class instance property value.
Does BLoCProvider used only once in a class?
===> I'm asking those question because i see that BLoC working with 'Equatable' and that in a the state class there is always a need to bring default value to the state we provide to the view class.
Another Question (what change the view and operate the state):
Does i need to bring always a list in order for example to update an item from the list or only changing the state+emit(in cubit) will change the state of the application, maybe it realted to BLocListener?
I would like my toggle buttons to be layout in a table, and not as a single row.
The number of toggle buttons is not static -
that is upon init I load a resource which contains a list of all the texts that should become the toggle buttons.
Looked at a number of approaches, each has its issues:
Create a list of ToggleButtons and a list of lists of bools to store the appropriate selected state as a data structure to divide the toggle buttons into a number of rows. The problem with this approach is in the implementation of the onPressed method - how to get a reference to the appropriate element in the list of lists of bools? Or in other words - how to get a reference to ToggleButtons object from within the onPressed method?
Use key property to pass the index of the current ToggleButtons. It is not intended for this purpose, so it is a bad practice, also again, there seems to be no straightforward way to access the key property from the onPressed method.
Extend the ToggleButtons class, and specifically override its build method. This is considered an anti-pattern in Flutter in general. Specifically In this approach, as we want all the functionality to remain the same, and change only the internal Row -> Table widget generation in the build method, it looks like we would have to duplicate all the code of this method, which is a bad idea as it might brake things as it changes in future versions of this widget
Create a table of checkbox / switch widgets as an alternative, which should work easily, but I want the look & feel of toggle buttons, not checkboxes or switches :)
I must be missing something simple!
After posting this I have a new idea :)
A table of FlatButtons! Will be probably possible to achieve similar UI to ToggleButtons. Will try it in a bit.
I would still love to hear other suggestions regarding ToggleButtons.
Try using SwitchListTile.
The entire list tile is interactive: tapping anywhere in the tile toggles the switch. Tapping and dragging the Switch also triggers the onChanged callback.
To ensure that onChanged correctly triggers, the state passed into value must be properly managed. This is typically done by invoking State.setState in onChanged to toggle the state value.
The value, onChanged, activeColor, activeThumbImage, and inactiveThumbImage properties of this widget are identical to the similarly-named properties on the Switch widget.
The title, subtitle, isThreeLine, and dense properties are like those of the same name on ListTile.
The selected property on this widget is similar to the ListTile.selected property, but the color used is that described by activeColor, if any, defaulting to the accent color of the current Theme. No effort is made to coordinate the selected state and the value state; to have the list tile appear selected when the switch is on, pass the same value to both.
The switch is shown on the right by default in left-to-right languages (i.e. in the ListTile.trailing slot) which can be changed using controlAffinity. The secondary widget is placed in the ListTile.leading slot.
To show the SwitchListTile as disabled, pass null as the onChanged callback.
I have an issue with the provider pattern, I have a solution to my problem i just wanted to check its a good method and if there a better alternates.
I am trying to update the text controllers text when they first load the widget to have the value stored in my provider state. Originally, I just created the text controller in the init and just loaded the state in the build method and set the controllers text.
This was working until i wanted to have some validation of the content that would prevent certain things being passed into the state ( for example preventing empty strings).
textController.addListener(() {
if( RULE ABOUT WHETHER TO SET STATE BASED ON TEXT){
state.textField = textController.text;
}
});
The problem arose here, as they user would delete their word and this would fail the rule. The rebuild would occur (as they had pressed a key) and the text.controller would then rebuild to what was in the state (a single letter as it failed the rule). Effectively this prevented them from deleting, which is something i want them to be able to do but for this not to update the state.
I found this library https://pub.dev/packages/after_layout which allows a method to be overridden which is called once immediately after the build.
My solution uses this by creating the text controller in the initstate.
Assigning it to the TextField in the build.
Then creating a local field that would maintain the textField widget string content.
Then in the new afterbuild method i would assign whats on the state to the variable and update the text controllers text to have this value.
Then in the text.controllers text changed listener I used my rule to only update this state if it met the rule. Therefore if they deleted content they shouldn't be able to and closed/reopened the widget the state would rebuild to still have a valid value.
Is using this library a good solution to this or is there a better technique?
---------------- EDIT
Sorry for my wordy first part. I think my main question is just how am i meant to init Controllers if the data i need has to come from the state in the build.
For example.
// This must go in the build as it requires state
myTabsController = TabController(length: myState.list.length, vsync: this);
I'm initialisng the controller every time it builds now... How am i meant to put this in the init but still access the state variables.
(I've tried using the afterFirstLayout() callback from the AfterLayoutMixin but that just causes more problems.
Feel free to ask me to clarify more.
Thanks for your help.
First note that I am not referring to any specific framework or technology like XAML.
The question is how to implement the MvvM pattern using ICommand for selection of an item in a list (=clicking a row)?
I have a view model (pseudo code):
class ListViewModel
{
// Items in the list.
public ObservableCollection<T> Items {};
// Command for item selection.
public ICommand ItemSelectedCommand
{
...
}
// Select an item in the list.
public void SelectItem(int index)
{
...
}
// The current selected item.
public T SelectedItem
{
get { ... };
}
}
How would I now connect my UI to that view model "manually"? Say, for instance in an iOS application.
I would probably have a UITableViewController, get an instance of the view model and populate the UITableView contents from it. Then I would trigger the ICommand from the RowSelected() method.
And here comes the thing I don't understand: how does the view model now know which item index was selected? I don't want to call SelectItem() because then I would not need the loosely coupled ICommand at all.
And maybe here we have to look how it is solved in XAML to understand the trick?
Coming from XAML and WPF, there are two options to forward selection changes from the UI to the ViewModel (as I understand your question, you're not asking about the other way around - feedbacking changes in the ViewModel to the UI - here):
Command with payload
The ICommands Execute method has a payload parameter. Executing a command without a payload can be done passing null:
SomeCommand.Execute(null);
In your case, it would make sense to pass the selected item as the parameter in the event handler:
vm.ItemSelectedCommand.Execute(eventArgs.SelectedItem);
or
vm.ItemSelectedCommand.Execute(myList.SelectedItem);
In the command's execution method, you can handle the parameter. Note that your ViewModel property SelectedItem is not directly involved here. If you need the selected index explicitly (which is not the case, usually), I would check the selected item's index in the Items collection.
Binding selected item of list to a ViewModel property
Option B is to 'bind' the selected item of the list to a distinct property on the ViewModel, in your case the SelectedItem property in the event handler of the list:
vm.SelectedItem = myList.SelectedItem;
The command is kind of redundant then, although you could invoke it without a payload after setting SelectedItem on the ViewModel. I would rather handle the change of the selected item in the set accessor of the property on the ViewModel.
Note: XAML and WPF come with quite a lot of infrastructure code out of the box. MVVM doesn't make sense without a proper framework to actually take care of binding UI and ViewModels in a loosely coupled way. You quickly end up with a lot of extra work and little benefit, because you're still maintaining tight dependencies. Bottom line: I recommend getting or writing a proper MVVM framework, before actually implementing it.
i learned how to implement my own SuggestionOracle("AuSuggestOracle") and own
Suggestions("AuMultiWordSuggestion"). In my case the suggestion object
is constructed with a DTO. On a selection event i need this dto (or
some fields of it) to react appropriate.
I implemented a widget containing 3 suggest boxes with this special
oracle and some logic between them. Now i want to apply MVP pattern -
split this widget in presenter and view.
At the moment the presenters display interface look like that:
public interface Display {
HasSelectionHandlers<Suggestion> getFedLand();
HasSelectionHandlers<Suggestion> getCounty();
HasSelectionHandlers<Suggestion> getCommunity();
AuSuggestOracle getFedLandOracle();
AuSuggestOracle getCountyOracle();
AuSuggestOracle getCommunityOracle();
void clearCounty();
void clearCommunity();
void activateForm();
Widget asWidget();
}
the problem is the implicit knowledge about my model in methods
returning "AuSuggestOracle". so my question is how to get the view/
interface "humble". in my case the displayed suggestion-strings are
ambiguous and i need at least the "id" of a selected item to know what
DTObject is selected.
The way I got around this is by leaving out the getters for the Oracle since once my presenter sets it my view doesn't need any information about it. So, my interface looked like this:
public interface Display {
...
void setSuggestionOracle(SuggestOracle oracle);
HasSelectionHandlers<SuggestOracle.Suggestion> getSelectionListener();
}
The problem I encountered was being able to add the suggestion to the SuggestBox after it was instantiated. To get around this, I initialized with a blank SuggestBox and then removed it from the view, updated in, and inserted it back into position.
After that, you can write your handler (in the presenter) to check if the suggestion is an instance of your custom suggestion and your presenter can handle the selection and push the relevant information back down to your view.
By doing this, all your view knows is that it will be taking generic suggestions for something, and that at some later time it will be updating with information (which will be as a result of the suggestion, but the view is to 'humble' to know that).