File access sample

//*********************************************************
//
// Copyright (c) Microsoft. All rights reserved.
// THIS CODE IS PROVIDED *AS IS* WITHOUT WARRANTY OF
// ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING ANY
// IMPLIED WARRANTIES OF FITNESS FOR A PARTICULAR
// PURPOSE, MERCHANTABILITY, OR NON-INFRINGEMENT.
//
//*********************************************************

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.ViewManagement;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

namespace SDKTemplate.Common
{
    /// <summary>
    /// Typical implementation of Page that provides several important conveniences:
    /// application view state to visual state mapping, GoBack and GoHome event handlers, and
    /// a default view model.
    /// </summary>
    [Windows.Foundation.Metadata.WebHostHidden]
    public class LayoutAwarePage : Page
    {
        /// <summary>
        /// Identifies the <see cref="DefaultViewModel"/> dependency property.
        /// </summary>
        public static readonly DependencyProperty DefaultViewModelProperty =
            DependencyProperty.Register("DefaultViewModel", typeof(IObservableMap<String, Object>),
            typeof(LayoutAwarePage), null);

        private List<Control> _layoutAwareControls;

        /// <summary>
        /// Initializes a new instance of the <see cref="LayoutAwarePage"/> class.
        /// </summary>
        public LayoutAwarePage()
        {
            if (Windows.ApplicationModel.DesignMode.DesignModeEnabled) return;

            // Create an empty default view model
            this.DefaultViewModel = new ObservableDictionary<String, Object>();

            // Map application view state to visual state for this page when it is part of the visual tree
            this.Loaded += this.StartLayoutUpdates;
            this.Unloaded += this.StopLayoutUpdates;
        }

        /// <summary>
        /// An implementation of <see cref="IObservableMap&lt;String, Object&gt;"/> designed to be
        /// used as a trivial view model.
        /// </summary>
        protected IObservableMap<String, Object> DefaultViewModel
        {
            get
            {
                return this.GetValue(DefaultViewModelProperty) as IObservableMap<String, Object>;
            }

            set
            {
                this.SetValue(DefaultViewModelProperty, value);
            }
        }

        /// <summary>
        /// Invoked as an event handler to navigate backward in the page's associated
        /// <see cref="Frame"/> until it reaches the top of the navigation stack.
        /// </summary>
        /// <param name="sender">Instance that triggered the event.</param>
        /// <param name="e">Event data describing the conditions that led to the event.</param>
        protected virtual void GoHome(object sender, RoutedEventArgs e)
        {
            // Use the navigation frame to return to the topmost page
            if (this.Frame != null)
            {
                while (this.Frame.CanGoBack) this.Frame.GoBack();
            }
        }

        /// <summary>
        /// Invoked as an event handler to navigate backward in the page's associated
        /// <see cref="Frame"/> to go back one step on the navigation stack.
        /// </summary>
        /// <param name="sender">Instance that triggered the event.</param>
        /// <param name="e">Event data describing the conditions that led to the
        /// event.</param>
        protected virtual void GoBack(object sender, RoutedEventArgs e)
        {
            // Use the navigation frame to return to the previous page
            if (this.Frame != null && this.Frame.CanGoBack) this.Frame.GoBack();
        }

        /// <summary>
        /// Invoked as an event handler, typically on the <see cref="Loaded"/> event of a
        /// <see cref="Control"/> within the page, to indicate that the sender should start
        /// receiving visual state management changes that correspond to application view state
        /// changes.
        /// </summary>
        /// <param name="sender">Instance of <see cref="Control"/> that supports visual state
        /// management corresponding to view states.</param>
        /// <param name="e">Event data that describes how the request was made.</param>
        /// <remarks>The current view state will immediately be used to set the corresponding
        /// visual state when layout updates are requested.  A corresponding
        /// <see cref="Unloaded"/> event handler connected to <see cref="StopLayoutUpdates"/>
        /// is strongly encouraged.  Instances of <see cref="LayoutAwarePage"/> automatically
        /// invoke these handlers in their Loaded and Unloaded events.</remarks>
        /// <seealso cref="DetermineVisualState"/>
        /// <seealso cref="InvalidateVisualState"/>
        public void StartLayoutUpdates(object sender, RoutedEventArgs e)
        {
            var control = sender as Control;
            if (control == null) return;
            if (this._layoutAwareControls == null)
            {
                // Start listening to view state changes when there are controls interested in updates
                Window.Current.SizeChanged += this.WindowSizeChanged;
                this._layoutAwareControls = new List<Control>();
            }
            this._layoutAwareControls.Add(control);

            // Set the initial visual state of the control
            VisualStateManager.GoToState(control, DetermineVisualState(ApplicationView.Value), false);
        }

        private void WindowSizeChanged(object sender, Windows.UI.Core.WindowSizeChangedEventArgs e)
        {
            this.InvalidateVisualState();
        }

        /// <summary>
        /// Invoked as an event handler, typically on the <see cref="Unloaded"/> event of a
        /// <see cref="Control"/>, to indicate that the sender should start receiving visual
        /// state management changes that correspond to application view state changes.
        /// </summary>
        /// <param name="sender">Instance of <see cref="Control"/> that supports visual state
        /// management corresponding to view states.</param>
        /// <param name="e">Event data that describes how the request was made.</param>
        /// <remarks>The current view state will immediately be used to set the corresponding
        /// visual state when layout updates are requested.</remarks>
        /// <seealso cref="StartLayoutUpdates"/>
        public void StopLayoutUpdates(object sender, RoutedEventArgs e)
        {
            var control = sender as Control;
            if (control == null || this._layoutAwareControls == null) return;
            this._layoutAwareControls.Remove(control);
            if (this._layoutAwareControls.Count == 0)
            {
                // Stop listening to view state changes when no controls are interested in updates
                this._layoutAwareControls = null;
                Window.Current.SizeChanged -= this.WindowSizeChanged;
            }
        }

        /// <summary>
        /// Translates <see cref="ApplicationViewState"/> values into strings for visual state
        /// management within the page.  The default implementation uses the names of enum values.
        /// Subclasses may override this method to control the mapping scheme used.
        /// </summary>
        /// <param name="viewState">View state for which a visual state is desired.</param>
        /// <returns>Visual state name used to drive the
        /// <see cref="VisualStateManager"/></returns>
        /// <seealso cref="InvalidateVisualState"/>
        protected virtual string DetermineVisualState(ApplicationViewState viewState)
        {
            return viewState.ToString();
        }

        /// <summary>
        /// Updates all controls that are listening for visual state changes with the correct
        /// visual state.
        /// </summary>
        /// <remarks>
        /// Typically used in conjunction with overriding <see cref="DetermineVisualState"/> to
        /// signal that a different value may be returned even though the view state has not
        /// changed.
        /// </remarks>
        public void InvalidateVisualState()
        {
            if (this._layoutAwareControls != null)
            {
                string visualState = DetermineVisualState(ApplicationView.Value);
                foreach (var layoutAwareControl in this._layoutAwareControls)
                {
                    VisualStateManager.GoToState(layoutAwareControl, visualState, false);
                }
            }
        }

        /// <summary>
        /// Implementation of IObservableMap that supports reentrancy for use as a default view
        /// model.
        /// </summary>
        private class ObservableDictionary<K, V> : IObservableMap<K, V>
        {
            private class ObservableDictionaryChangedEventArgs : IMapChangedEventArgs<K>
            {
                public ObservableDictionaryChangedEventArgs(CollectionChange change, K key)
                {
                    this.CollectionChange = change;
                    this.Key = key;
                }

                public CollectionChange CollectionChange { get; private set; }
                public K Key { get; private set; }
            }

            private Dictionary<K, V> _dictionary = new Dictionary<K, V>();
            public event MapChangedEventHandler<K, V> MapChanged;

            private void InvokeMapChanged(CollectionChange change, K key)
            {
                var eventHandler = MapChanged;
                if (eventHandler != null)
                {
                    eventHandler(this, new ObservableDictionaryChangedEventArgs(CollectionChange.ItemInserted, key));
                }
            }

            public void Add(K key, V value)
            {
                this._dictionary.Add(key, value);
                this.InvokeMapChanged(CollectionChange.ItemInserted, key);
            }

            public void Add(KeyValuePair<K, V> item)
            {
                this.Add(item.Key, item.Value);
            }

            public bool Remove(K key)
            {
                if (this._dictionary.Remove(key))
                {
                    this.InvokeMapChanged(CollectionChange.ItemRemoved, key);
                    return true;
                }
                return false;
            }

            public bool Remove(KeyValuePair<K, V> item)
            {
                V currentValue;
                if (this._dictionary.TryGetValue(item.Key, out currentValue) &&
                    Object.Equals(item.Value, currentValue) && this._dictionary.Remove(item.Key))
                {
                    this.InvokeMapChanged(CollectionChange.ItemRemoved, item.Key);
                    return true;
                }
                return false;
            }

            public V this[K key]
            {
                get
                {
                    return this._dictionary[key];
                }
                set
                {
                    this._dictionary[key] = value;
                    this.InvokeMapChanged(CollectionChange.ItemChanged, key);
                }
            }

            public void Clear()
            {
                var priorKeys = this._dictionary.Keys.ToArray();
                this._dictionary.Clear();
                foreach (var key in priorKeys)
                {
                    this.InvokeMapChanged(CollectionChange.ItemRemoved, key);
                }
            }

            public ICollection<K> Keys
            {
                get { return this._dictionary.Keys; }
            }

            public bool ContainsKey(K key)
            {
                return this._dictionary.ContainsKey(key);
            }

            public bool TryGetValue(K key, out V value)
            {
                return this._dictionary.TryGetValue(key, out value);
            }

            public ICollection<V> Values
            {
                get { return this._dictionary.Values; }
            }

            public bool Contains(KeyValuePair<K, V> item)
            {
                return this._dictionary.Contains(item);
            }

            public int Count
            {
                get { return this._dictionary.Count; }
            }

            public bool IsReadOnly
            {
                get { return false; }
            }

            public IEnumerator<KeyValuePair<K, V>> GetEnumerator()
            {
                return this._dictionary.GetEnumerator();
            }

            System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
            {
                return this._dictionary.GetEnumerator();
            }

            public void CopyTo(KeyValuePair<K, V>[] array, int arrayIndex)
            {
                int arraySize = array.Length;
                foreach (var pair in this._dictionary)
                {
                    if (arrayIndex >= arraySize) break;
                    array[arrayIndex++] = pair;
                }
            }
        }
    }
}