19 invitations to careers.stackoverflow.com giveaway

Maybe careers.stackoverflow.com will be useful for someone, so I have 19 invitations that I don’t need. Just click at this link: accept invitation.

invitations carreer stackexchange

The proposal remains valid as long as you see this post. If I don’t have invitations, I will delete the post.

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Windows Phone Marketplace app submitting

In this article I will show how the windows phone marketplace looks and how to publish apps there.

When you click the Submit App link, you will see the following page:
mainpage

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Windows Phone display images from URL

The built-in Image element is quite good for loading and displaying images from the web, because it loads them asynchronously in the background thread and doesn’t freeze UI.

In this example I will show how to display a loading indicator while the image is loading and an error message if the image loading has failed.

wp7_imageloading_loadingviewwp7_imageloading_imageview

You shouldn’t use the Source property in the XAML markup, instead you should set the Source property in the code-behind.

The XAML markup looks so:

<Grid x:Name="LayoutRoot" Background="Transparent">
    <TextBlock x:Name="loadingView" Visibility="Collapsed" Text="Loading..." VerticalAlignment="Center" HorizontalAlignment="Center" />
    <TextBlock x:Name="errorView" Visibility="Collapsed" VerticalAlignment="Center" HorizontalAlignment="Center" />
    <Image x:Name="imageView" Visibility="Collapsed" />
</Grid>

The code-behind:

public partial class MainPage : PhoneApplicationPage
{
    public MainPage()
    {
        InitializeComponent();

        var bitmap = new BitmapImage(new Uri("http://upload.wikimedia.org/wikipedia/commons/6/63/Wikipedia-logo.png"));
        bitmap.ImageFailed += (s, e) => this.ShowError("Error while loading the image.");
        bitmap.ImageOpened += (s, e) => this.ShowImage();

        this.ShowLoading();
        this.imageView.Source = bitmap;
    }

    private void ShowLoading()
    {
        this.loadingView.Visibility = Visibility.Visible;
        this.imageView.Visibility = Visibility.Collapsed;
        this.errorView.Visibility = Visibility.Collapsed;
    }

    private void ShowError(string message)
    {
        this.loadingView.Visibility = Visibility.Collapsed;
        this.imageView.Visibility = Visibility.Collapsed;
        this.errorView.Visibility = Visibility.Visible;

        this.errorView.Text = message;
    }

    private void ShowImage()
    {
        this.loadingView.Visibility = Visibility.Collapsed;
        this.imageView.Visibility = Visibility.Visible;
        this.errorView.Visibility = Visibility.Collapsed;
    }
}

At first I create the BitmapImage instance, after the creation of this object I subscribe to its events ImageFailed and ImageOpened. Then I display the loading indicator (the ShowLoading method). And as soon as the line ‘this.imageView.Source = bitmap’ is called, the image loading process starts. After some time either ShowError or ShowImage will be called.

The sample application you can download here: https://dl.dropbox.com/u/8047386/WordPress/PhoneImageLoadingSample.zip

My Windows Phone open source application

Though I know Windows Phone development in theory, I haven’t ever developed applications for this platform. That’s why I decided to create one application for one web site which provides json api. The site is an imageboard like 4chan, i.e all topics and messages are anonymous and you can attach images to your messages.

The source code is situated on my github account. I’ve already created an Android application for this web site and published it on Google Play, so it wasn’t so difficult to reimplement the application for Windows Phone. It is definitely much easier than to develop it from scratch.

The Windows Phone project is situated here.

So far the application looks like this:

wp1wp2wp3

At the moment the application has the following functionality:
1. Downloads and parses JSON files.
2. Displays the loading indicator during loading, displays the error message if an error has occured.
3. Loads and displays list images (thumbnails) asyncronously.
4. Opens full images in the WebBrowser.
5. Converts HTML posts to RichTextBox controls (the parser isn’t ideal, but it works at least for this website).
6. Makes HTTP POST requests.

By the way, the application is already published in the marketplace and available here: http://www.windowsphone.com/en-us/store/app/2ch-browser/3f63fa2c-4b35-4b8a-b3c0-51b54b460d70

The certification process was without problems, but I had to wait 5 days.

Displaying progress bar while loading JSON from Web Services for Windows Phone 7

In one of my previous posts I explained how to download and parse JSON response from web services. I used a simple text to show that the content is loading, but it isn’t convenient because you don’t know how long it remains to wait. In this post I will add the ProgressBar control to the project which will constantly display the number of downloaded bytes in per cents.
Here is how it looks:
wp7_json_loading
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Windows 8 calendar control

As far as I see, lot of people search how to add the calendar or datepicker control to their windows 8 applications. Though there is a control which is called WinJS.UI.DatePicker, it is actually not a date picker, it is just 3 comboboxes in one row. But because of the fact that Windows Store apps can be written by using HTML, CSS and Javascript, you can use any HTML controls which was designed for web sites in the internet. Here is a link to a short review of 21 free HTML datepickers.

In this post I will show how to use the most popular JQuery UI Datepicker. You should build your Windows Store app by using Javascript, because for obvious reasons it won’t work with XAML and C# (though you can try to use this control for C# apps, but I’m not sure that it will work).
Here is the screenshot of the app running on the simulator:

win8-calendar

At first, it is necessary to download 3 files. Though it is possible for internet web sites to refer to javascript libraries without downloading them, windows store applications can’t do this, they can use only offline javascript files.
1. jQuery 1.8.3 (the latest stable version at the moment of writing this post, but you can use any other version)
2. jQuery UI
3. jQuery UI style sheet

The first thing that you should do is to modify the jQuery 1.8.3 library. You should add 1 line at the beginning of the file and 1 line at the end:

MSApp.execUnsafeLocalFunction(function () {
// the original file
});

Like this:

win8-jquery-modified

Then add these 3 files to appropriate folders of the project:

winstore_datepicker_sample_solution_explorer

Add links to these files to the head section and add an input element with javascript code to the body section. The whole file looks so:

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title>DatePicker Sample</title>

    <link href="//Microsoft.WinJS.1.0/css/ui-dark.css" rel="stylesheet" />
    <script src="//Microsoft.WinJS.1.0/js/base.js"></script>
    <script src="//Microsoft.WinJS.1.0/js/ui.js"></script>
    
    <script src="/js/jquery-1.8.3.js"></script>
    <script src="/js/jquery-ui.js"></script>
    <link href="/css/jquery-ui.css" rel="stylesheet" />

<!-- These links are not necessary in my application, but they can be useful in other applications -->
<!--<link href="/css/default.css" rel="stylesheet" />
    <script src="/js/default.js"></script>-->
</head>
<body>
    <h1>DatePicker Sample</h1>
    <p>Date: <input type="text" id="datepicker" /></p>

    <script type="text/javascript">
        $("#datepicker").datepicker();
    </script>
</body>
</html>

The source code of the sample application: WinStoreDatepickerSample.zip

Silverlight and WP7 chart with data point labels

Recently I found the question on stackoverflow in which one user asked how to add labels to data points on WPF/Silverlight/Windows Phone Toolkit charts. Whereas almost every javascript chart can do this, this functionality is absent in Silverlight charts and none of developers cares.

So I wrote a simple class which extended the LinearSeries class and now line charts can be displayed like this:

silverlight_chart_datapointlabels

wp7_chart_datapointlabels

I added labels only for line charts, but if someone needs them for column charts, I can try to implement it as well.
In the current implementation I created the class which inherits the LineSeries class. It has the following properties:
DisplayLabels – You should set it to true explicitly so that labels are displayed. It is false by default.
LabelBindingPath – Optional. You can specify a custom property of your model which will be displayed instead of the value from the Y-axis.
LabelStyle – Optional. You can change foreground, font weight, font size and other properties of labels.

The example of usage:

<chart:Chart Width="600" Height="300">
    <local:ExtendedLineSeries
        ItemsSource="{Binding Items}"
        DependentValuePath="ItemValue"
        IndependentValuePath="Title" 
        DisplayLabels="True"
        LabelBindingPath="ItemValue" />
</chart:Chart>

The complete source code of the class:

public class ExtendedLineSeries : LineSeries
{
    private Canvas _labelsCanvas;
    private Dictionary<DataPoint, TextBlock> _currentLabels = new Dictionary<DataPoint, TextBlock>();

    /// <summary>
    /// Gets or sets a value indicating whether labels should be displayed. 
    /// </summary>
    public bool DisplayLabels { get; set; }

    /// <summary>
    /// Gets or sets the binding path of the label.
    /// </summary>
    public string LabelBindingPath { get; set; }

    /// <summary>
    /// Gets or sets the style of each label.
    /// </summary>
    public Style LabelStyle { get; set; }

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();

        // get a canvas to which the labels will be added
        this._labelsCanvas = (Canvas)this.GetTemplateChild("PlotArea");
        // clear the clip property so that labels are visible even if they exceed the bounds of the chart
        this.Clip = null;
    }

    protected override void UpdateDataPoint(DataPoint dataPoint)
    {
        base.UpdateDataPoint(dataPoint);

        // after the data point is created and added to the chart, we can add a label near it
        if (this.DisplayLabels && dataPoint.Visibility == System.Windows.Visibility.Visible)
        {
            Deployment.Current.Dispatcher.BeginInvoke(() => this.CreateLabel(dataPoint));
        }
    }

    private void CreateLabel(DataPoint dataPoint)
    {
        // this method is also called with the SizeChanged event, so I create the label only one time
        TextBlock label;
        if (this._currentLabels.ContainsKey(dataPoint))
        {
            label = this._currentLabels[dataPoint];
        }
        else
        {
            label = new TextBlock();
            this._labelsCanvas.Children.Add(label);
            this._currentLabels.Add(dataPoint, label);

            label.Style = this.LabelStyle;

            // bind the label text to the specified path, or to dataPoint.DependantValue by default
            Binding binding = this.LabelBindingPath != null
                        ? new Binding(this.LabelBindingPath) { Source = dataPoint.DataContext }
                        : new Binding("DependentValue") { Source = dataPoint };
            BindingOperations.SetBinding(label, TextBlock.TextProperty, binding);
        }

        // calculate a position of the label
        double coordinateY = Canvas.GetTop(dataPoint) - label.ActualHeight; // position the label above the data point
        double coordinateX = Canvas.GetLeft(dataPoint) + dataPoint.ActualHeight / 2 - label.ActualWidth / 2; // center horizontally
        Canvas.SetTop(label, coordinateY);
        Canvas.SetLeft(label, coordinateX);
    }
}

In this code I made an override of the UpdateDataPoint method and each time a DataPoint is updated I update its label.
The code work with Silverlight as well as with Windows Phone 7. For WP7 I used the recompiled library which I published in one of my previous posts.

Source code of the sample application: ChartPointLabelsSample.zip