I'm writing an app using Xamarin Forms and I have an issue I was hoping someone can help with.
My app contains a screen which has multiple icons that can be pressed which would then open a new screen.
My issue is that if you press the icon twice really fast, the app opens up 2 instances of the same screen (it's not just related to a double press, if you press the icon 6 times very fast it will open up 6 duplicate screens). Pressing the Back button, closes the top screen to reveal the duplicate screen underneath. Pressing the Back button again navigates you back to the original screen.
This issue seems to occur on any screen within my app so I'm hoping other people will have experienced it and know of a solution to prevent duplicate screens being displayed.
This is a known issue in TapEvents.
My hack is, in the code-behind, have a bool variable _canTap.
Inside the method you are calling to push new page, first you check if canTap, then set to false, and only set to true after navigating to another page. This way all taps will be disregarded.
Example:
private bool _canTap = true;
public void YourMethod()
{
if(_canTap)
{
_canTap = false;
YourMethodToNavigate();
_canTap = true;
}
}
In the Icon_Pressed method add this,
this.IsEnabled = false;
await Navigation.PushAsync(new MyPage());
this.IsEnabled = true;
It disables the page until the current Icon pressed event is finished
This is known problem with Xamarin apps. I've used a private variable combined with a try-finally pattern to solve this. Ex:
bool allowTap = true;
public void ButtonTapped()
{
try
{
if(allowTap)
{
allowTap = false;
// Do whatever...
}
}
finally
{
allowTap = true;
}
}
The finally makes sure allowTap gets set back to true no matter what happens, short of a complete crash. Note that you can also use a catch block between the try and finally blocks to grab any errors if needed.
Related
I am building a Xamarin Forms mobile app that runs in Android on a Zebra scanner. I flip 2 different StackLayouts to IsVisble true/false to display different stuff in the UI. (StackLayout1 and StackLayout2)
The customer wants the user to be able to use the app entirely from the hardware keyboard on the scanner. So I have used the device Settings so that it never displays the virtual keyboard (I don’t think that matters for the issue I am having.)
I am overriding DispatchKeyEvent in a PageRenderer in the Android project and everything is working great … except.
The problem case:
StackLayout1 is displayed
the user taps an Entry control, putting the focus there
the user taps a button in the UI
the app displays StackLayout2
at this point the DispatchKeyEvent never fires no matter what key I press on the device keyboard
If an Entry box does NOT get the focus (step #2 above) the DispatchKeyEvent always fires in StackLayout2 and the StackLayouts display as expected.
If I programatically put the focus in an Entry box in StackLayout2 at step #3 above the DispatchKeyEvent fires fine.
That is not an OK solution. I have tried to progamatically put the focus on StackLayout2, and that code seems to do what is expected but DispatchKeyEvent does not fire.
Maybe I need to do something in the Android-project PageRenderer so that it is aware of StackLayout2 when it is made IsVisible = true.
Update 2: I found that I did NOT need custom StackLayouts. The solution which I posted below does not include any of this stuff I am describing in Update 1 (sorry, if that's confusing).
Update 1:
I added a ViewRenderer for both StackLayouts, and the code is hitting the OnElementChanged event when StackLayout2's IsVisible property flips to true, just great. Although the problem case is the same: DispatchKeyEvent does not fire once StackLayout2 is displayed, if an EntryBox had the focus in StackLayout1
Here is the OnElementChanged part of the new StackLayout ViewRenders
async void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
switch (e.PropertyName)
{
case "IsVisible":
if (Element.IsVisible)
{
if (sender is StackLayout)
{
this.FocusableViewAvailable(this); // if I comment these 2 lines out I get the same bad result
this.Focusable = true; // if I comment these 2 lines out I get the same bad result
this.FocusableInTouchMode = true;
var dd = this.RequestFocus(); // this is always false
var ee = this.IsFocused; // this is always false
}
}
break;
}
}
Also, as I am pointing out in the comments ^ there, IsFocused is always false.
Ideas?
My hunch, "Maybe I need to do something in the Android project PageRenderer" was correct. In the DispatchKeyEvent I had to make the MainPage have the focus when the keypress was handled.
Here is what the DispatchKeyEvent looks like now (notice the comments):
public override bool DispatchKeyEvent(KeyEvent ke)
{
// MainPage.ReceiveKeyPress(e); is the method that this method returns to
bool KeyPressWasHandled = false;
KeyPressWasHandled = (Element as MainPage).ReceiveKeyPress(ke);
if (KeyPressWasHandled)
{
// this next block seems to be needed so that this class
// continues to receive the keypress event after an Entry box has had the focus
this.Focusable = true;
this.FocusableInTouchMode = true;
this.RequestFocus();
return true; // returning true tells the parent class that the keypress has been handled
} else
{
try
{
return base.DispatchKeyEvent(ke);
}
Now the "problem case" in my initial post is no longer a problem.
NOTE: I found that I did NOT need the custom ViewRenderers that I had made for the StackLayouts.
I am using xamarin.forms for an Android application, where I need to display an alert with YES on left side and NO on the right side. I can manage it swapping YES to NO and NO to YES, but when outside of the alert is clicked by default it is taking as YES.
How can I achieve that?
I use something like this and it works quite well, even though it has come to my attention that it might not be future-proof. If the user doesn't click on YES, the display just disappears without doing anything else.
bool continue_logout = false;
try
{
continue_logout = await DisplayAlert("Logout", "If you logout, you also clear the cache of all data. Are you sure you want to continue?", "Yes", "No");
if (continue_logout)
{
// Clean up stuff and clear out user settings
}
}
catch {
}
finally
{
if (continue_logout)
App.Current.MainPage = new NavigationPage(new LoginPage());
}
I have implemented a clickable Frame in Xamarin.Forms 2.3.4 with a custom FrameRenderer that set Clickable (and LongPressable FWIW) to true, subscribed the respective events and set the FrameRenderers foreground
TypedValue typedValue = new TypedValue();
this.Context.Theme.ResolveAttribute(Android.Resource.Attribute.SelectableItemBackground, typedValue, true);
this.Foreground = this.Resources.GetDrawable(typedValue.ResourceId, this.Context.Theme);
to achieve Material motion (ripple touch).
After updating to XF 2.5 (most likely as of 2.3.5, since fast renderers have been introduced with that release) my touch events have ceased to work. My custom renderer is assigned correctly, so are the Clickable and LongPressable properties, but nothing happens. Partially I have been able to work around the issue - at least for the moment - by subscribing to FrameRenderer.Touch and call OnClick from that event handler. This renders the app usable, but unfortunately lacks the visual feedback in form of the ripple touch effect.
Is there any way I can restore the original behavior? Is there any way to implement a clickable frame with ripple touch in XF 2.5?
With the help of this answer I have figured out a solution. Here's a draft of it:
First of all I store a local reference to my RippleDrawable (see documentation)
private void SetMaterialMotion()
{
TypedValue typedValue = new TypedValue();
this.Context.Theme.ResolveAttribute(Android.Resource.Attribute.SelectableItemBackground, typedValue, true);
this.Foreground = this.Resources.GetDrawable(typedValue.ResourceId, this.Context.Theme);
this._layerDrawable = this.Foreground as RippleDrawable;
}
then I have to subscribe to the Touch event
private void SubscribeClickEvent()
{
if (this.ClickableFrame.IsClickable)
{
this.Touch += ClickableFrameRenderer_Touch;
}
}
In my ClickableFrameRenderer_Touch I set the Pressed property and the hotspot of the RippleDrawable
private void ClickableFrameRenderer_Touch(object sender, TouchEventArgs e)
{
if(e.Event.Action == Android.Views.MotionEventActions.Down)
{
this.Pressed = true;
}
if(e.Event.Action == Android.Views.MotionEventActions.Up)
{
this._layerDrawable.SetHotspot(e.Event.GetX(), e.Event.GetY());
this.Pressed = false;
}
}
This will show the ripple touch motion (more or less) as expected. Of course this does not handle long presses, yet, but I'm on a way.
Anyway, this is not a solution I like very much. I still think that there has to be a supported way on making FastRenderers.FrameRenderer clickable. If anyone knows it: Please share your knowledge.
Issue:
I'm dealing with an issue on how to disable the background on a DisplayActionSheet or DisplayAlert in Xamarin Forms, so the only way the user can "get out" of the popup windows is via the options that the window has prompted.
Here is the screenshot of the problem:
http://postimg.org/image/s16cp66wf/
Do you know if there's a simple way to do this? I've been looking but I couldn't found....
I tried:
Using the methods that came with the control but nothing else came up. What I'm doing right now is to call it till I have an answer.
Code:
From my code behind I call the event
async void OnNextClicked(object sender, EventArgs args)
{
await userValidations.RMLocationServiceWindow();
}
And then I call the popup window
public async Task RMLocationServiceWindow ()
{
string rta = null;
while (rta == null)
{
rta = await App.Current.MainPage.DisplayActionSheet("Do you accept to use the service?", "Cancel", "Continue");
}
}
I couldn't find any that keep the focus on the windows.
Unfortunately this could not be done in displayactionsheet, for you to be able to achieve this, you must create a Modal Page with list where you could be able to disable back button until there is a selection on the list. hope it helps
I think I got your problem. If your problem is about when user not click 'Cancel' or 'Continue' and he click empty space, you wont get value for rta. Think about if user click white space it mean is canceling. This way may help you.
while (rta == null)
{
rta = await App.Current.MainPage.DisplayActionSheet("Do you accept to use the service?", "Cancel", "Continue");
if (rta==null)
rta=="Cancel";
}
I'm writing a program using Qt 4.8 that displays a table (QTableWidget) filled with filenames and file's params. First an user adds files to the list and then clicks process. The code itself updates the contents of the table with simple progress description. I want the table by default to be scrolled automatically to show the last processed file and that code is ready.
If I want to scroll it by hand the widget is being scrolled automatically as soon as something changes moving the viewport to the last element. I want to be able to override the automated scroll if I detect that it was the user who wanted to change view.
This behavior can be seen in many terminal emulator programs. When there's a new line added the view is scrolled but when user forces the terminal to see some previous lines the terminal does not try to scroll down.
How could I do that?
Solution:
I created an object which filters event processed by my QTableWidget and QScrollBar embedded inside. If I spot the event that should turn off automatic scrolling I just set a flag and stop scrolling view if that flag is set.
Everything is implemented inside tableController class. Here are parts of three crucial methods.
bool tableController::eventFilter(QObject* object, QEvent* event)
{
switch (event->type())
{
case QEvent::KeyPress:
case QEvent::KeyRelease:
case QEvent::Wheel:
case QEvent::MouseButtonDblClick:
case QEvent::MouseButtonPress:
case QEvent::MouseButtonRelease:
_autoScrollEnabled = false;
default:
break;
}
return QObject::eventFilter(object, event);
}
void tableController::changeFile(int idx)
{
[...]
if (_autoScrollEnabled)
{
QTableWidgetItem* s = _table.item(_engine.getLastProcessed(), 1);
_table.scrollToItem(s);
}
[...]
}
void tableController::tableController()
{
[...]
_autoScrollEnabled = true;
_table.installEventFilter(this);
_table.verticalTableScrollbar()->installEventFilter(this);
[...]
}
Thanks for all the help. I hope somebody will find it useful :)
Subclass QTableWidget and overload its wheelEvent. You can use the parameters of the supplied QWheelEvent object in order to determine if the user scrolled up or down.
Then use a simple boolean flag which is set (or reset) in your wheelEvent override. The method which is responsible for calling scrollToBottom() should then consider this boolean flag.
You will have to find a way to figure out when to set or reset that flag, e.g. always set it when the user scrolls up and reset it when the user scrolls down and the currently displayed area is at the bottom.
connect(_table->view()->verticalScrollBar(), &QAbstractSlider::actionTriggered, this, [this](int) {
_autoScrollEnabled = false;
});