Redux seems to be a very nice architecture for mobile app development. However, mobile apps have some features that are not common for web apps.
In my case, I would like to start long polling /monitoring location/tracking file system (any action that watches some external state) after the start of some particular screen and stop when the screen is closed.
Let's say we have a function, that can emit multiple events over time.
Stream<Event>monitor();
I would like to listen to the function only when some particular screen is active.
What is the best way of doing that?
Suppose you have 3 pages: 'PageHome.dart', 'Page1.dart', 'Page2.dart'.
Create another dart file 'GlobalVariables.dart', create a class gv inside this file, create static redux 'stores' for the three pages.
create static var strCurPage in gv.
suppose each page has a variable that is to be changed by an external event, declare them in gv as static var also.
Codes in GlobalVariables.dart:
import 'package:redux/redux.dart';
enum Actions {
Increment
}
// The reducer, which takes the previous count and increments it in response to an Increment action.
int reducerRedux(int intSomeInteger, dynamic action) {
if (action == Actions.Increment) {
return intSomeInteger + 1;
}
return intSomeInteger;
}
class gv {
static Store<int> storePageHome =
new Store<int>(reducerRedux, initialState: 0);
static Store<int> storePage1 =
new Store<int>(reducerRedux, initialState: 0);
static Store<int> storePage2 =
new Store<int>(reducerRedux, initialState: 0);
static String strCurPage = 'PageHome';
static String strPageHomeVar = 'PageHomeInitialContent';
static String strPage1Var = 'Page1InitialContent';
static String strPage2Var = 'Page2InitialContent';
}
Import 'GlobalVariables.dart' in all other dart files.
Before navigate to a new page, e.g. from PageHome to Page1, set:
gv.strCurPage = 'Page1';
Inside your monitor function, if an external event happens, say, change the values of the variables in Page1 and Page2 (But user currently navigating in Page1):
void thisFunctionCalledByExternalEvent(strPage1NewContent, strPage2NewContent) {
gv.strPage1Var = strPage1NewContent;
gv.strPage2Var = strPage2NewContent;
if (gv.strCurPage == 'Page1') {
// Dispatch storePage1 to refresh Page 1
storePage1.dispatch(Actions.Increment);
} else if (gv.strCurPage == 'Page2') {
// Dispatch storePage2 to refresh Page 2
storePage2.dispatch(Actions.Increment);
} else {
// Do not need to refresh page if user currently navigating other pages.
// so do nothing here
}
}
I don't know whether this is the best way, but using redux and GlobalVariables.dart, I can:
know which page the user is currently navigating.
change the content of a page even when the user is not at that page when the event fires. (But the content will be shown when the user navigate to that page later)
force the user to go to a specific page no matter which page the user is navigating, when the event fires.
Related
I try the new Shell of Xamarin Form 4 for a small project.
I have a list of order, then someone chooses an order and start picking some inventory for this order with barcode. To be simple, I use 2 views and 2 viewmodel.
The process is:
1. User select an order the click a button "pickup"
2. I use ViewModelLocator (TinyIoc) to resolve the correct ViewModel of the pickup view
3. I call Initialize on the new ViewModel and pass some parameters needed. Like a list of items needed to be pickup.
4. Open the view in modal state.
I don't understand that if I change some qty in the list I pass on the second viewmodel, then hit the back button (modal view close). The quantity changed is now in the original viewmodel. How this is possible? I was thinking that passing parameter to a function do not share the same variable but just copy it??
Viewmodel of the first view (look at the Initialize function the List passed and the JobEnCours object)
private async Task GoPickup()
{
Device.BeginInvokeOnMainThread(async () =>
{
if (this.CodeJob != null && this.CodeJob != "")
{
this.IsBusy = true;
PrepChariotSP3ViewModel vm = ViewModelLocator.Resolve<PrepChariotSP3ViewModel>();
await vm.InitializeAsync(this._jobEnCours, this.ComposantesPick.ToList()) ;
await Shell.Current.Navigation.PushAsync(new PrepChariotSP3Page(vm));
this.IsBusy = false;
}
});
}
the the Initialize code on the second Viewmodel (look I set the JobEnCours.Description=Test)
public async Task InitialiseAsync(Job jobEnCours, List<ComposantePick> composantePick)
{
Title = "Ceuillette: " + jobEnCours.CodeProd;
this._jobEnCours = jobEnCours;
this.ComposantesPick = new ItemsChangeObservableCollection<ComposantePick>();
foreach(ComposantePick c in composantePick)
{
this.ComposantesPick.Add(c);
}
jobEnCours.Description = "test";
So, If I do the back button, then in the first VM the JobEnCours.Description is now set to "test" how this is possible?!
Any idea?
Based on the project tracker I have integrated a changelog into my app that relates my UserSettings model to a UserHistory model. The latter contains the fields FieldName, CreatedBy, CreatedDate, OldValue, NewValue.
The relation between both models works fine. Whenever a record is modified, I can see the changes in a changelog table. I now want add an "undo"-button to the table that allows the admin to undo a change he clicks on. I have therefore created a method that is handled by the widget that holds the changelog record:
function undoChangesToUserRecord(changelog) {
if (!isAdmin()) {
return;
}
var fieldName = changelog.datasource.item.FieldName;
var record = changelog.datasource.item.UserSettings;
record[fieldName] = changelog.datasource.item.OldValue;
}
In theory method goes the connection between UserHistory and UserSettings up to the field and rewrites its value. But when I click on the button, I get a "Failed due to circular reference" error. What am I doing wrong?
I was able to repro the issue with this bit of code:
google.script.run.ServerFunction(app.currentPage.descendants.SomeWidget);
It is kinda expected behavior, because all App Maker objects are pretty much complex and Apps Script RPC has some limitations.
App Maker way to implement it would look like this:
// Server side script
function undoChangesToUserRecord(key) {
if (!isAdmin()) {
return;
}
var history = app.models.UserHistory.getRecord(key);
if (history !== null) {
var fieldName = history.FieldName;
var settings = history.UserSettings;
settings[fieldName] = history.OldValue;
}
}
// Client side script
function onUndoClick(button) {
var history = widget.datasource.item;
google.script.run
.undoChangesToUserRecord(history._key);
}
I have an activity indicator on xaml page. Initially its IsVisible property is false. I have a button on page. When user click on button it calls a web service to get data. I change the value of IsVisible property to true before calling the service so that activity indicator starts to display on page and after successful calling of service I change its value to again false so that it doesn't show any more on page.
But it is not working. I know the actual problem. When we call the web service the UI thread gets block and it doesn't show the activity indicator.
How I can enable the UI thread when web service gets called so that activity indicator can show on page until we get the data?
Try making your webservice call into an async and await it.
Depending on how you've structured things you may have to use a TaskCompletionSource as the following example demonstrates.
In this example when the button is clicked, the button is made invisible, and the ActivityIndicator is set to IsRunning=True to show it.
It then executes your long running task / webservice in the function ExecuteSomeLongTask using a TaskCompletionSource.
The reason for this is that in our button click code, we have the final lines:-
objActivityIndicator1.IsRunning = false;
objButton1.IsVisible = true;
That stop the ActivityIndicator from running and showing, and also set the button back to a visible state.
If we did not use a TaskCompletionSource these lines would execute immediately after calling the ExecuteSomeLongTask if it was a normal async method / function, and would result in the ActivityIndicator not running and the button still being visible.
Example:-
Grid objGrid = new Grid()
{
};
ActivityIndicator objActivityIndicator1 = new ActivityIndicator();
objGrid.Children.Add(objActivityIndicator1);
Button objButton1 = new Button();
objButton1.Text = "Execute webservice call.";
objButton1.Clicked += (async (o2, e2) =>
{
objButton1.IsVisible = false;
objActivityIndicator1.IsRunning = true;
//
bool blnResult = await ExecuteSomeLongTask();
//
objActivityIndicator1.IsRunning = false;
objButton1.IsVisible = true;
});
objGrid.Children.Add(objButton1);
return objGrid;
Supporting function:-
private Task<bool> ExecuteSomeLongTask()
{
TaskCompletionSource<bool> objTaskCompletionSource1 = new TaskCompletionSource<bool>();
//
Xamarin.Forms.Device.StartTimer(new TimeSpan(0, 0, 5), new Func<bool>(() =>
{
objTaskCompletionSource1.SetResult(true);
//
return false;
}));
//
return objTaskCompletionSource1.Task;
}
You need to do your work in an asynchronous way. Or in other words: Use Asnyc & Await to ensure, that you UI works well during the call.
You can find more informations in the Xamarin Docs.
async and await are new C# language features that work in conjunction
with the Task Parallel Library to make it easy to write threaded code
to perform long-running tasks without blocking the main thread of your
application.
If you need further asistance, please update your question and post your code or what you have tried so far.
I have an ASP.NET Web Forms application. I want to have a button to post back to the server that will use my fields on my form (after validation) as parameters to a server process that will generate a document and stream it back to the browser. I want the form to be updated with some status results.
What is the best way to achieve this? Right now, I've got the button click generating the document and streaming it back to the browser (it's a Word document and the dialog pops up, and the Word document can be opened successfully) but the page doesn't get updated.
I have jQuery in my solution, so using js isn't an issue if that is required.
I have a very similar process on one of my servers, and the way I've handled it is to create a temporary document on the server rather than doing a live stream. It requires a bit of housekeeping code to tidy it up, but it does mean that you can return the results of the generation and then do a client-side redirect to the generated document if successful. In my case, I'm using jQuery and AJAX to do the document generation and page update, but the same principle should also apply to a pure WebForms approach.
This was way more difficult to do than I thought. The main issue is with opening a new browser window for a Word document. The window briefly flashes up, then closes - no Word document appears. It seems to be a security issue.
If i click a button on my page, I can stream the Word doc back as the response, and the browser dialog pops up allowing me to Open/Save/Cancel, but of course, my page doesn't refresh.
My final solution to this was to use a client script on the button click to temporarily set the form's target to _blank. This forces the response to the click on the postback to go to a new browser window (which automatically closes after the download dialog is dismissed):
<asp:Button Text="Generate Doc" runat="server" ID="btnGenerateDoc"
onclick="btnGenerateDoc_Click" OnClientClick="SetupPageRefresh()" />
My SetupPageRefresh function is as follows:
function SetupPageRefresh() {
// Force the button to open a new browser window.
form1.target = '_blank';
// Immediately reset the form's target back to this page, and setup a poll
// to the server to wait until the document has been generated.
setTimeout("OnTimeout();", 1);
}
Then my OnTimeout function resets the target for the form, then starts polling a web service to wait until the server process is complete. (I have a counter in my Session that I update once the process has completed.)
function OnTimeout() {
// Reset the form's target back to this page (from _blank).
form1.target = '_self';
// Poll for a change.
Poll();
}
And the Poll function simply uses jQuery's ajax function to poll my web service:
function Poll() {
var currentCount = $("#hidCount").val();
$.ajax({
url: "/WebService1.asmx/CheckCount",
data: JSON.stringify({ currentCount: currentCount }),
success: function (data) {
var changed = data.d;
if (changed) {
// Change recorded, so refresh the page.
window.location = window.location;
}
else {
// No change - check again in 1 second.
setTimeout("Poll();", 1000);
}
}
});
}
So this does a 1 second poll to my web service waiting for the Session's counter to change from the value in the hidden field on the page. This means it doesn't matter how long the server process takes to generate the Word document (and update the database, etc.) the page won't refresh until it's done.
When the web service call comes back with true, the page is refreshed with the window.location = window.location statement.
For completeness, my Web Service looks like this:
/// <summary>
/// Summary description for WebService1
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.ComponentModel.ToolboxItem(false)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
[System.Web.Script.Services.ScriptService]
public class WebService1 : WebService
{
[WebMethod(EnableSession=true)]
public bool CheckCount(int currentCount)
{
if (Session["Count"] == null)
Session["Count"] = 0;
var count = (int)Session["Count"];
var changed = count != currentCount;
return changed;
}
}
Hopefully that helps somebody else!
I have some problem that happens when controls are loaded in init and it still doesn't help me to get proper postback event fired on time.
I am trying to create a rich wizard control that will enable switching, links with description, completely customized steps, integration of substeps - by using dynamic control load that is avoids standard asp.net wizard way of loading.
Idea is to have on left part navigation, on right part content, or substeps that are run from right part and that go over whole area.
Download source project
Ok, I re-read the question, and here is what you have to do. You have to re-load these controls on each postback, give them always the same "Id". This can be done in Page_Init or in Page_Load event. And of course, you have to re-attach event handlers on each post back.
Many thanks.. well i found the answer - id was the problem, in load control method. I was doing this wizard.. well most of things work now.
If someone is interested to see how does this works.. there are some updates:
public void LoadSplitViewControl(string path)
{
SwitchNavigationView(NavigationView.SplitView);
LastNavigationView = NavigationView.SplitView;
LoadControl(SplitControlLoader, path, "LoadedControlSplit");
}
public void LoadSingleViewControl(string path)
{
SwitchNavigationView(NavigationView.SingleView);
LastNavigationView = NavigationView.SingleView;
LoadControl(SingleControlLoader, path, "LoadedControlSingle");
}
public void LoadSingleViewControlAsClear(string path)
{
SwitchNavigationView(NavigationView.SingleView);
LastNavigationView = NavigationView.SingleView;
LoadControlAsClear(SingleControlLoader, path, "LoadedControlSingle");
}
private void LoadControl(PlaceHolder holder, string path, string ID)
{
UserControl ctrl = (UserControl)Page.LoadControl(path);
ctrl.ID = ID;
LastControlPath = path;
holder.Controls.Clear();
holder.Controls.Add(ctrl);
}
//as i am using steps loaded controls using splitview and substeps controls using single view sometimes viewstate will not be valid so error will be thrown but u can resolve this by using LoadSingleViewControlAsClear that will load below method.
private void LoadControlAsClear(PlaceHolder holder, string path, string ID)
{
UserControl ctrl = (UserControl)Page.LoadControl(path);
ctrl.ID = ID;
LastControlPath = path;
ctrl.EnableViewState = false;
holder.Controls.Add(ctrl);
}
/another cool idea i am using for such an wizard is that i am not using viewstate but rather session object for saving values collected over steps. My session object key is generated by authenticated username and pageguid - so u can have many loaded pages and each of them will handle different session object./
public Guid PageGuid
{
get
{
if (PageGuidField.Value == "")
{
var _pageGuid = Guid.NewGuid();
PageGuidField.Value = _pageGuid.ToString();
return _pageGuid;
}
return new Guid(PageGuidField.Value);
}
}