WP8图片缩放功能实现

最近在学习WP8,想实现WP微信中查看图片时的放大缩小功能。

网上找了两个解决方案：

1 利用GestureListener

 这个类在Microsoft.Phone.Controls.Toolkit中，GestureListener可以捕捉到WP手机屏幕上的手势动作。

XAML文件：

<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
            <Image x:Name="_image" Source="/Assets/test.jpg"   RenderTransformOrigin="0.5,0.5">
                <Image.RenderTransform>
                    <ScaleTransform x:Name="transform"/>
                </Image.RenderTransform>
                <toolkit:GestureService.GestureListener>
                    <toolkit:GestureListener 
                        DoubleTap="OnDoubleTap"DragDelta="OnDragDelta"
                        Flick="OnFlick"
                        PinchStarted="OnPinchStarted" PinchDelta="OnPinchDelta" PinchCompleted="OnPinchCompleted"/>
                </toolkit:GestureService.GestureListener>
                
            </Image>
        </Grid>

cs文件：

       double initialScale;

        public Zoom()
        {
            InitializeComponent();
        }

        private void OnDoubleTap(object sender, Microsoft.Phone.Controls.GestureEventArgs e)
        {
            transform.ScaleX = transform.ScaleY = 1;
        }

        private void OnDragDelta(object sender, DragDeltaGestureEventArgs e)
        {
            transform.CenterX -= e.HorizontalChange;
            transform.CenterY -= e.VerticalChange;
        }

        private void OnPinchStarted(object sender, PinchStartedGestureEventArgs e)
        {
            initialScale = transform.ScaleX;
        }

        private void OnPinchDelta(object sender, PinchGestureEventArgs e)
        {
            transform.ScaleX = transform.ScaleY = initialScale * e.DistanceRatio;
        }

        private void OnPinchCompleted(object sender, PinchGestureEventArgs e)
        {
            
        }

        private void OnFlick(object sender, FlickGestureEventArgs e)
        {
            
        }

前面是在XAML代码中构建GestureListener，在后台代码中也可以构建GestureListener。

               Grid grd = new Grid
                {
                    Height = 800,
                    Width = 480,
                    Background = new SolidColorBrush(Colors.Black),
                    Opacity = 0.9,
                };

                Image img = new Image { Source = source };
                grd.Children.Add(img);
                //设置图片变换类型为缩放
                ScaleTransform transform = new ScaleTransform();
                img.RenderTransform = transform;
                
                var gesListener= GestureService.GetGestureListener(img);
               
                gesListener.DoubleTap += (obj, arg) =>
                    {
                        transform.ScaleX = transform.ScaleY = 1;
                    };
                gesListener.DragDelta += (obj, arg) =>
                    {
                        transform.CenterX -= arg.HorizontalChange;
                        transform.CenterY -= arg.VerticalChange;
                    };
                gesListener.PinchStarted += (obj, arg) =>
                    {
                        initialScale = transform.ScaleX;
                    };
                gesListener.PinchDelta += (obj, arg) =>
                {
                    transform.ScaleX = transform.ScaleY = initialScale * arg.DistanceRatio;
                };

2 ViewportControl

XAML文件：

       <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
            <ViewportControl x:Name="viewport"  
                ManipulationStarted="OnManipulationStarted" ManipulationDelta="OnManipulationDelta"  
                             ManipulationCompleted="OnManipulationCompleted" ViewportChanged="viewport_ViewportChanged">
                <Canvas x:Name="canvas">
                    <Image x:Name="TestImage" Source="/Assets/test.jpg"  
                            RenderTransformOrigin="0,0" CacheMode="BitmapCache"
                           ImageOpened="OnImageOpened">
                        <Image.RenderTransform>
                            <ScaleTransform x:Name="xform"/>
                        </Image.RenderTransform>
                    </Image>
                </Canvas>
            </ViewportControl>
        </Grid>

cs文件：

 const double MaxScale = 10;

        double _scale = 1.0;
        double _minScale;
        double _coercedScale;
        double _originalScale;

        Size _viewportSize;
        bool _pinching;
        Point _screenMidpoint;
        Point _relativeMidpoint;

        BitmapImage _bitmap; 


        public PinchAndZoom()
        {
            InitializeComponent();

            BuildLocalizedApplicationBar();
        }

        /// <summary> 
        /// Either the user has manipulated the image or the size of the viewport has changed. We only 
        /// care about the size. 
        /// </summary> 
        void viewport_ViewportChanged(object sender, System.Windows.Controls.Primitives.ViewportChangedEventArgs e)
        {
            Size newSize = new Size(viewport.Viewport.Width, viewport.Viewport.Height);
            if (newSize != _viewportSize)
            {
                _viewportSize = newSize;
                CoerceScale(true);
                ResizeImage(false);
            }
        }

        /// <summary> 
        /// Handler for the ManipulationStarted event. Set initial state in case 
        /// it becomes a pinch later. 
        /// </summary> 
        void OnManipulationStarted(object sender, ManipulationStartedEventArgs e)
        {
            _pinching = false;
            _originalScale = _scale;
        }

        /// <summary> 
        /// Handler for the ManipulationDelta event. It may or may not be a pinch. If it is not a  
        /// pinch, the ViewportControl will take care of it. 
        /// </summary> 
        /// <param name="sender"></param> 
        /// <param name="e"></param> 
        void OnManipulationDelta(object sender, ManipulationDeltaEventArgs e)
        {
            if (e.PinchManipulation != null)
            {
                e.Handled = true;

                if (!_pinching)
                {
                    _pinching = true;
                    Point center = e.PinchManipulation.Original.Center;
                    _relativeMidpoint = new Point(center.X / TestImage.ActualWidth, center.Y / TestImage.ActualHeight);

                    var xform = TestImage.TransformToVisual(viewport);
                    _screenMidpoint = xform.Transform(center);
                }

                _scale = _originalScale * e.PinchManipulation.CumulativeScale;

                CoerceScale(false);
                ResizeImage(false);
            }
            else if (_pinching)
            {
                _pinching = false;
                _originalScale = _scale = _coercedScale;
            }
        }

        /// <summary> 
        /// The manipulation has completed (no touch points anymore) so reset state. 
        /// </summary> 
        void OnManipulationCompleted(object sender, ManipulationCompletedEventArgs e)
        {
            _pinching = false;
            _scale = _coercedScale;
        }


        /// <summary> 
        /// When a new image is opened, set its initial scale. 
        /// </summary> 
        void OnImageOpened(object sender, RoutedEventArgs e)
        {
            _bitmap = (BitmapImage)TestImage.Source;

            // Set scale to the minimum, and then save it. 
            _scale = 0;
            CoerceScale(true);
            _scale = _coercedScale;

            ResizeImage(true);
        }

        /// <summary> 
        /// Adjust the size of the image according to the coerced scale factor. Optionally 
        /// center the image, otherwise, try to keep the original midpoint of the pinch 
        /// in the same spot on the screen regardless of the scale. 
        /// </summary> 
        /// <param name="center"></param> 
        void ResizeImage(bool center)
        {
            if (_coercedScale != 0 && _bitmap != null)
            {
                double newWidth = canvas.Width = Math.Round(_bitmap.PixelWidth * _coercedScale);
                double newHeight = canvas.Height = Math.Round(_bitmap.PixelHeight * _coercedScale);

                xform.ScaleX = xform.ScaleY = _coercedScale;

                viewport.Bounds = new Rect(0, 0, newWidth, newHeight);

                if (center)
                {
                    viewport.SetViewportOrigin(
                        new Point(
                            Math.Round((newWidth - viewport.ActualWidth) / 2),
                            Math.Round((newHeight - viewport.ActualHeight) / 2)
                            ));
                }
                else
                {
                    Point newImgMid = new Point(newWidth * _relativeMidpoint.X, newHeight * _relativeMidpoint.Y);
                    Point origin = new Point(newImgMid.X - _screenMidpoint.X, newImgMid.Y - _screenMidpoint.Y);
                    viewport.SetViewportOrigin(origin);
                }
            }
        }

        /// <summary> 
        /// Coerce the scale into being within the proper range. Optionally compute the constraints  
        /// on the scale so that it will always fill the entire screen and will never get too big  
        /// to be contained in a hardware surface. 
        /// </summary> 
        /// <param name="recompute">Will recompute the min max scale if true.</param> 
        void CoerceScale(bool recompute)
        {
            if (recompute && _bitmap != null && viewport != null)
            {
                // Calculate the minimum scale to fit the viewport 
                double minX = viewport.ActualWidth / _bitmap.PixelWidth;
                double minY = viewport.ActualHeight / _bitmap.PixelHeight;

                _minScale = Math.Min(minX, minY);
            }

            _coercedScale = Math.Min(MaxScale, Math.Max(_scale, _minScale));

        }

        // Sample code for building a localized ApplicationBar
        private void BuildLocalizedApplicationBar()
        {
            // Set the page's ApplicationBar to a new instance of ApplicationBar.
            ApplicationBar = new ApplicationBar();

            // Create a new button and set the text value to the localized string from AppResources.
            ApplicationBarIconButton appBarButton = new ApplicationBarIconButton(new Uri("/Assets/appbar_info.png", UriKind.Relative));
            appBarButton.Click += appBarButton_Click;
            appBarButton.Text = AppResources.AppBarButtonInfoText;
            ApplicationBar.Buttons.Add(appBarButton);

        }

        void appBarButton_Click(object sender, EventArgs e)
        {
            MessageBox.Show(AppResources.PinchZoomHelpText, AppResources.InfoCaption,MessageBoxButton.OK);
        }

 PS:测试的话应该部署到WP8手机中测试。

参考：

http://www.cnblogs.com/chengxingliang/archive/2011/08/15/2137377.html

http://www.cnblogs.com/JerryH/archive/2012/01/05/2312635.html

http://code.msdn.microsoft.com/wpapps/Image-Recipes-0c0b8fee