execute asynctask on View Pager only page selected - android-asynctask

How to make execute asynctask on View Pager only page selected / opened?
like friendcaster for android execute asynctask when page opened. Or like tabhost method only execute when page opened, but when move to other tabs and back again not reload again.
thanks before. :D

Add that code to your pages:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
You can have AsyncTask in your first page class, for example, and call it from your ViewPager class.

Related

I want to set an onClick listener for custom view in sketchware

{final Button tab3button2 = view findViewById(R.id.button2); View.OnClickListener() { #Override pubilc void onClick (View v)
I have tried searching for answers but all to no avail.
Just copy the code for on click on source code, and you must have a section like bindview or webview to get at the id of widget. Then just enter I'd, make sure it's different then all others on same page.
Here is what you need, I edited your code:
final Button tab3button2 = view findViewById(R.id.button2);
tab3button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View _view) {
here put the blocks that will be executed when the button gets clicked
}
});
it's recommended to add this code in the onCreate event, but if this Button is in a ListView custom view then add it in the onBindCustomView event.

How to create a custom WebView Control Xamarin forms

I am trying to create a custom control for webview, i am trying to get a checkbox inside a webview Reason :- we have a bunch of text to be displayed and unless the user reaches the end of the scroll he cannot move to the next page and at the end of the scroll there is a checkbox where user has to check the the checkbox and then he can process. here i have tried putting the checkbox and webview inside the stacklayout but the issue is webview have its own scroll bar and and stacklayout scroll bar does not work when a user try to scroll as the webview scroller scrolls out also when i try to close the Webview Page with back button the webview gets close and not the page
i am not sure what approach should i apply here.
i am getting my html data from my webapi.
anyone with some solution would be appreciable
here is my custom renderer which i have wrote but the piece missing here is how can i add another xamarin control inside this
public class CustomPdfViewRenderer : WebViewRenderer
{
public CustomPdfViewRenderer(Context context) : base(context)
{
}
protected override void OnElementChanged(ElementChangedEventArgs<WebView> e)
{
base.OnElementChanged(e);
if (Control != null)
{
Control.Settings.BuiltInZoomControls = true;
Control.Settings.DisplayZoomControls = false;
Control.Settings.LoadWithOverviewMode = true;
Control.Settings.UseWideViewPort = true;
}
}
}
You can try the following approach:
Add checkbox to HTML
When the user check checkbox call some JavaScript function
When JavaScript function is called, call C# function (Xamarin) which will enable the user to process to the next page (or some other Xamarin side stuff)
Here is how you can call C# function from JavaScript :HybridWebView

CarouselView not showing on Android if in a modal page

I am trying to handle a login/registration form inside a CarouselView (https://github.com/alexrainman/CarouselView). In my MainPage, I have this:
protected override async void OnAppearing()
{
base.OnAppearing();
// Is user logged in?
if (!(bool)Application.Current.Properties["IsLoggedIn"]) // He is not logged in
{
await this.Navigation.PushModalAsync(new LoginRegistrationPage());
}
}
LoginRegistrationPage contains a CarouselView and its first page is the registration form, while the second page is the login form.
iOS is fine, but on Android I get a blank page. The CarouselView is visible everywhere except that in a modal page. (I have tried to set LoginRegistrationPage as MainPage and to put it inside a simple Navigation rather than a modal one, both work).
It was a bug of CarouselView.
This solved: https://github.com/alexrainman/CarouselView/pull/329

How to override the functionality of Back button when using Navigation Controller in Xamarin.ios?

I'm working on Xamarin.iOS.When i move from one view controller to another a navigation bar is added to the view on which i just moved and a back button appears. On clicking the back button it returns me to the parent view. But i want some different functionality rather than returning to the parent view.
Can anyone help me out!
This can be accomplished by creating a custom button, and then setting that button as the back button for the view controller, such as:
public override void ViewDidLoad()
{
base.ViewDidLoad();
// Perform any additional setup after loading the view, typically from a nib.
UIBarButtonItem backButton = new UIBarButtonItem("title", UIBarButtonItemStyle.Bordered, handleBack);
this.NavigationItem.LeftBarButtonItem = backButton;
}
public void handleBack(object sender, EventArgs e)
{
Console.WriteLine("back!");
}
I hope this helps!

How to load MainPage when goBack(); form SecondPage?

I use NavigationService.Navigate("..."). But I want to load MainPage again when I click the Back button by event goBack();
In your goBack method you can use the NavigationService.GoBack() call to move from SecondPage back to the MainPage. You can view all the Navigation methods available to you on MSDN.
You can override the method OnBackKeyPress, and inside the method write code shown below, it ll navigate to MainPage.xaml
protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
{
NavigationService.Navigate(new Uri("/MainPage.xaml", UriKind.Relative));
}
If you are using binding do this:
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
App.ViewModel.LoadData();
}
And in MainViewModel.cs
public void LoadData()
{
Items.Clear();
this.Items.Add(new ItemViewModel() { LineOne = "runtime one", LineTwo = "Data info 2" });
this.IsDataLoaded = true; }
Like Nigel said, you can use NavigationService.GoBack() however this will only work if you went from the MainPage to the second page.
The only other way to do this is how you have mentioned using NavigationService.Navigate(uri).
Override the navigated to event
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
if (PhoneApplicationService.Current.State["msg"].ToString() == "from page2")
{
// do something when its comming from page2
}
base.OnNavigatedTo(e);
}
Now that will trigger every time its navigated to but you could send some parameters so you know what to depending on what page it came from.
PhoneApplicationService.Current.State["msg"] = "from page2";
NavigationService.Navigate(new Uri("/MainPage.xaml?msg=", UriKind.Relative));
There are two ways to get back to your MainPage.
(First Method) Override the OnBackKeyPress() and write the following snippet inside it.
NavigationService.GoBack();
Note :
This will move to the MainPage only if the MainPage is the previous page in your Navigation history.
(Second Method) Override the OnBackKeyPress() and write the following snippet inside it.
NavigationService.Navigation(new Url("/MainPage.xaml",UriKind.Relative));
Note :
This will create a New MainPage and navigates to it. So if you navigated from MainPage to SecondPage and if you navigate again to MainPage using the above snippet, you will be having two MainPage in your Navigation history.
So, use any one of the snippet according to your scenario.
if WP7 or WP8 : NavigationService.GoBack()
if WP8.1 : Frame.GoBack();
and you can Override the navigated to event
protected override void
OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e) {
// do nothing }
I don't recommend overriding the OnBackKeyPress method and calling NavigationService.Navigate method within it as it may mess up your page back stack.
I assume your app has more than 2 pages. Otherwise you should just call NavigateService.GoBack() as others have recommended.
Example
Start on MainPage (backstack: empty)
Navigate to SecondPage (backstack: MainPage)
Navigate to ThirdPage (backstack: SecondPage, MainPage)
Click the back button (overridden) and you are taken to MainPage (backstack: ThirdPage, SecondPage, MainPage)
Click the back button and you are taken to the ThirdPage (backstack: SecondPage, MainPage). This is not the expected behaviour as the application should have exited.
Now you're stuck in a back button loop.
Solution
Override OnNavigatingFrom and remove any of the backstack entries you don't want the user to go to. You can either allow the user to press the back button to get back to the MainPage from the ThirdPage or you can call NavigationService.GoBack().
protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
{
base.OnNavigatingFrom(e);
// Remove all backstack entries except for the first one
while(NavigationService.BackStack.Count() > 1)
{
NavigationService.RemoveBackEntry();
}
}

Resources