Tag Archives: Windows Phone

Windows-Phone-7-logo

Another way to close Windows Phone application from code


Correction

In my previous post on how to terminate the Windows Phone application i proposed a solution that is not really in accordance with Windows Phone Marketplace Technical Cerification Requirements (see requirement 5.1.2):

” An application that closes unexpectedly fails certification. ”

Even though I’m pretty sure that this requirement is not enforced since my apps use this approach and they were never rejected i decided to present another way.

Some good people suggested in comments of my previous post that you can terminate current application  simply by calling the XNA Game class Exit method like this:

using Microsoft.Xna.Framework;

namespace Roboblob
{
    public class AppLifetimeHelper
    {
        public void CloseApplication()
        {
            new Game().Exit();
        }
    }
}

The downside of this is that you need to add 2 XNA dll’s to your project:

  1. Microsoft.Xna.Framework
  2. Microsoft.Xna.Framework.Game
So there you have both approaches and you can choose which one is better for you until Microsoft exposes standardized way of closing application from code (i hope this will happen in Windows Phone 8 APIs).

Windows-Phone-7-logo

How to terminate your Windows Phone application programmatically?


21/08/2012 Update: 

There is another way to close the Windows Phone application without throwing exception see more details in my next post.

We want full power!

Its known that in Windows Phone API there is no easy way to terminate the current application from your code.

I guess makers of the platform did not wanted us developers to mingle with the application lifetime too much, phone should decide when an app is not needed and terminate it.

But i just simply cannot help myself, i always like to have full control, for example in my Offline Browser application i want to end the app if user presses the hardware Back Key multiple times in short time intervals.

Because there is this annoying situation when user goes navigating between the pages in your app (main screen, then settings, then about screen,

then again main screen etc) and then when he wants to terminate it he need to click the hardware back button N number of times in order to close it.

And even in some other situations its needed to force close the app, for example if some change in application settings requires app restart etc.

Show Us The Code!

So i decided to change this and wrote this simple AppLifetimeHelper that allows you to terminate your current app without any delay.

How it works is that it uses Application.Current.RootVisual and casts it to PhoneApplicationFrame that has RemoveBackEntry method that basically simulates

the users hardware Back Key press and then in endless loop it calls this method until the navigation back stack of the app is empty.

Then all we need to do is to call the GoBack method of the PhoneApplicationFrame and it will terminate the app since there are no more entries in the app Back Stack.

Simple or what?   8-)

So here is the code if you AppLifetimeHelper that you can freely use in your apps if you need this functionality:


using System.Linq;
using System.Windows;
using Microsoft.Phone.Controls;

namespace Roboblob
{
    public class AppLifetimeHelper
    {
        public void CloseApplication()
        {
            ClearApplicationNavigationBackStack();
            Root.GoBack();
        }

        private PhoneApplicationFrame _root;
        private PhoneApplicationFrame Root
        {
            get
            {
                if (_root == null)
                {
                    _root = Application.Current.RootVisual as PhoneApplicationFrame;
                }

                return _root;
            }
        }

        private void ClearApplicationNavigationBackStack()
        {
            if (Root == null)
            {
                return;
            }

            try
            {
                while (Root.BackStack.Any())
                {
                    Root.RemoveBackEntry();
                }
            }
            catch
            { }
        }
    }
}

And if you are really lazy today…

Here is the download link to the Visual Studio solution with Windows Phone application that uses this helper to terminate it self when a button is clicked…

Using Instapaper and other Mobilizer services in Offline Browser for Windows Phone

Mobile is the future!

Its a known fact that mobile usage of internet is growing.

More and more people are using primarily their phones and tablets to browse the web. Yet many websites are still not optimized for small screen devices.

My application Offline Browser for Windows Phone allows you to save whole web pages for later offline reading, but what to do if the website is not optimized for mobile devices?

Mobilize it!

This is where the concept of Mobilizer Services comes in.

Offline Browser supports multiple web services that can transform given web page into simpler version, where only content and images are kept and all other ‘noise’ is removed.

Here is the list of currently supported Mobilizers:

  1. Instapaper – currently the best option, creates clean output and preserves images
  2. Google Mobilizer – not so nice because it pages the content
  3. ReadItLater (now known as Pocket) – very nice but removes images

Each of those services are different and they give better or worse results when simplifying the webpage content – it often varies from website to website.

I prefer Instapaper since it gives cleanest output and shows images but you should try each of them to see which one is best for webpages you are opening.

Important thing to note here is that when Offline Browser uses these Mobilizer services to get the simplified content of web pages, all the images are saved to the phone and are available later when you view those pages when offline.

Another benefit of using Mobilizer service is that they reduce the bandwidth usage so if you have some tariff plan with limited number of MB this could help you keep the bandwidth usage as low as possible – not to mention that saving pages via Mobilizer is much faster!

So how do we enable this cool feature?

We just go to the Offline Browser Settings page and switch on this feature and choose which Mobilizer service we want to use.

Here is how this screen looks on the Windows Phone:

Once we enable the Mobilizer service all the pages we save to the phone storage are retrieved via the chosen Mobilizer and when you actually read the page you will see the mobilized version instead of the full webpage.

Here is how one of the web pages looks before using mobilizer:

As you can see webpage is not optimized for mobile devices and its not easy to read on the phone.

I deliberately used desktop browser user agent in the app Settings just to prove the point.

If we now switch to using Instapaper Mobilizer in the app Settings (and we still use the same desktop browser user agent) we will get completely different content:

As you see page is much easier to read, all the images are preserved.

Yet page is saved faster and less bandwidth is wasted.

So why not always use it?

Well i do use this all the time and only when Mobilizer services fail to retrieve content of some web page, then i switch it off and load original page content.

It all depends on your usage scenario and also on your data plan limits/internet connection speed etc.

Important thing is that you do have a choice and you can setup Offline Browser to work how its most convenient for you.

If you have any feedback regarding Mobilizers feature or you know of some good Mobilizer service that i should include in the app please send me a feedback via the Offline Browser Uservoice page and i will be glad to include it!

Windows-Phone-7-logo

Throttling Immediate TextBox Binding Behavior for Windows Phone

The learning curve of a Windows Phone developer

While developing Offline Web Browser for Windows Phone i had to build a small MVVM framework in order to keep the logic out of the views.

One of the first thing i found missing was a way to force immediate propagation of text entered in TextBox control to the databound property of my ViewModel.

By default, TextBox binding is triggered only when control loses focus, and this is kind of lame.

Code reuse is not a myth!

This is really old problem. It existed in desktop Silverlight from the beginning. And it made its way to the Windows Phone platform.

Fortunately I remembered that back in the days while experimenting with Silverlight MVVM framework i already solved this problem by creating a custom silverlight TextBox control so i decided to just reuse that code and create a Behavior that will force binding update to fire on each keystroke in TextBox.

That’s the beauty of developing a Windows Phone app – you can reuse most of the Silverlight code you built over the years :)

But then i noticed another problem. Because now each keystroke was propagating changes to my ViewModel, if user would type fast and i do for example some web service call on each property change – then i can have too many requests to the web service (one for each keystroke) but in fact i want to do a call only when user stopped typing for a while.

Fortunately, solution is very simple – we will use Reactive Extensions (Rx) since its perfect fit and its already built-in into Windows Phone.

We just need to reference Microsoft.Phone.Reactive.dll from GAC (no additional download needed) and we are half-way there.

OK, but show us some code!

Yes lets see how the code for the ThrottledImmediateBindingBehavior looks like:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Interactivity;
using Microsoft.Phone.Reactive;

namespace Roboblob.Mvvm.Behaviors
{
    public class ThrottledImmediateBindingBehavior : Behavior
    {
        private BindingExpression _expression;

        public bool Throttle { get; set; }

        private double _throttleDelayInSeconds = 0.5;
        private IDisposable _currentObservable;

        public double ThrottleDelayInSeconds
        {
            get { return _throttleDelayInSeconds; }
            set { _throttleDelayInSeconds = value; }
        }

        protected override void OnAttached()
        {
            base.OnAttached();

            if (Throttle)
            {
                this._expression = this.AssociatedObject.GetBindingExpression(TextBox.TextProperty);
                var keys = Observable.FromEvent(AssociatedObject, "TextChanged").Throttle(TimeSpan.FromSeconds(ThrottleDelayInSeconds));
                _currentObservable = keys.ObserveOn(Deployment.Current.Dispatcher).Subscribe(evt => OnTextChanged(evt.Sender, evt.EventArgs));
            }
            else
            {
                this._expression = this.AssociatedObject.GetBindingExpression(TextBox.TextProperty);
                this.AssociatedObject.TextChanged += this.OnTextChanged;
            }
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();

            if (Throttle)
            {
                if (_currentObservable != null)
                {
                    _currentObservable.Dispose();
                    this._expression = null;
                }
            }
            else
            {
                this.AssociatedObject.TextChanged -= this.OnTextChanged;
                this._expression = null;
            }
        }

        private void OnTextChanged(object sender, EventArgs args)
        {
            if (_expression != null)
            {
                this._expression.UpdateSource();
            }
        }
    }
}

Simple Is Beautiful

Our Binding class has bool property Throttle where we can enable/disable throttling and also a ThrottleDelayInSeconds where we specify after how many seconds later after user stops typing our property is updated.

In the OnAttached – we just hook to the TextChanged and each time user types something we update the binding source.

But if Throttle is set to true, we hook to the TextChanged event over Reactive Extensions and we setup throttling so that binding do not trigger if changes are too fast.

In this only after changes stop firing for the time defined in ThrottleDelayInSeconds, only then binding update is triggered.

Off course we do a little cleanup in the OnDetaching as all good coders :)

What about the Xaml???

Yes in Xaml we can use it like this:

            <TextBox Text="{Binding SearchCriteriaText, Mode=TwoWay}">
                <i:Interaction.Behaviors>
                    <RoboblobBehaviors:ThrottledImmediateBindingBehavior Throttle="True" ThrottleDelayInSeconds="1" />
                </i:Interaction.Behaviors>
            </TextBox>

For those who are lazy to type I’m attaching a zipped source code of simple Windows Phone Mango project that is demonstrating the usage of the behavior.

Btw does somebody even remember how it was to type source code from printed computer magazines int your 8bit computer?

Probably not :D

Well at least I hope that someone will find this useful.

Until next time, happy coding!