作为本专栏的第一篇，必不可少的需要介绍一下图像的打开与保存，一便大家后面DEMO的制作。
Win8Metro编程中，图像相关的操作基本都是以流的形式进行的，图像对象类型在Metro主要表现为两种形式：BitmapImage和WriteableBitmap，图像的显示控件为Image。
我们可以用如下方式打开和显示一幅图像对象。
BitmapImage srcImage=newBitmapImage (new Uri(“UriPath”), UriKind.Relative)
其中UriPath为图像的Uri地址，UriKind表示路径的选择，Urikind.Relative表示是相对路径，也可以选择绝对路径Urikind.Absolute，或者Urikind. RelativeOrAbsolute。
Image imageBox=newImage ();
imageBox.Source=srcImage;//将图像显示在imageBox控件中
还有一种方法则是使用WriteableBitmap对象，这也是我这里要详细介绍的方法。
1.图像打开
privatestaticBitmapImage srcImage =newBitmapImage();
privatestaticWriteableBitmap wbsrcImage;
//open image fuctiondefinition
privateasyncvoid OpenImage()
{
FileOpenPicker imagePicker =newFileOpenPicker
{
ViewMode = PickerViewMode.Thumbnail,
SuggestedStartLocation =PickerLocationId.PicturesLibrary,
FileTypeFilter = { ".jpg",".jpeg",".png",".bmp" }
};
Guid decoderId;
StorageFile imageFile =await imagePicker.PickSingleFileAsync();
if (imageFile !=null)
{
srcImage = newBitmapImage();
using (IRandomAccessStream stream =await imageFile.OpenAsync(FileAccessMode.Read))
{
srcImage.SetSource(stream);
switch (imageFile.FileType.ToLower())
{
case".jpg":
case".jpeg":
decoderId = Windows.Graphics.Imaging.BitmapDecoder.JpegDecoderId;
break;
case".bmp":
decoderId = Windows.Graphics.Imaging.BitmapDecoder.BmpDecoderId;
break;
case".png":
decoderId = Windows.Graphics.Imaging.BitmapDecoder.PngDecoderId;
break;
default:
return;
}
Windows.Graphics.Imaging.BitmapDecoder decoder =await Windows.Graphics.Imaging.BitmapDecoder.CreateAsync(decoderId, stream);
int width = (int)decoder.PixelWidth;
int height = (int)decoder.PixelHeight;
Windows.Graphics.Imaging.PixelDataProvider dataprovider =await decoder.GetPixelDataAsync();
byte[] pixels =dataprovider.DetachPixelData();
wbsrcImage = newWriteableBitmap(width, height);
Stream pixelStream =wbsrcImage.PixelBuffer.AsStream();
//rgba in original
//to display ,convert tobgra
for (int i = 0; i < pixels.Length; i += 4)
{
byte temp = pixels[i];
pixels[i] =pixels[i + 2];
pixels[i +2] = temp;
}
pixelStream.Write(pixels, 0, pixels.Length);
pixelStream.Dispose();
stream.Dispose();
}
ImageOne.Source =wbsrcImage;
ImageOne.Width =wbsrcImage.PixelWidth;
ImageOne.Height =wbsrcImage.PixelHeight;
}
}
2.图像保存
//save image fuction definition
privateasyncvoid SaveImage(WriteableBitmap src)
{
FileSavePicker save =newFileSavePicker();
save.SuggestedStartLocation =PickerLocationId.PicturesLibrary;
save.DefaultFileExtension =".jpg";
save.SuggestedFileName ="newimage";
save.FileTypeChoices.Add(".bmp",newList<string>() { ".bmp" });
save.FileTypeChoices.Add(".png",newList<string>() { ".png" });
save.FileTypeChoices.Add(".jpg",newList<string>() { ".jpg",".jpeg" });
StorageFile savedItem =await save.PickSaveFileAsync();
try
{
Guid encoderId;
switch (savedItem.FileType.ToLower())
{
case".jpg":
encoderId =BitmapEncoder.JpegEncoderId;
break;
case".bmp":
encoderId =BitmapEncoder.BmpEncoderId;
break;
case".png":
default:
encoderId =BitmapEncoder.PngEncoderId;
break;
}
IRandomAccessStream fileStream =await savedItem.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);
BitmapEncoder encoder =awaitBitmapEncoder.CreateAsync(encoderId, fileStream);
Stream pixelStream =src.PixelBuffer.AsStream();
byte[] pixels =newbyte[pixelStream.Length];
pixelStream.Read(pixels, 0, pixels.Length);
//pixal format shouldconvert to rgba8
for (int i = 0; i < pixels.Length; i += 4)
{
byte temp = pixels[i];
pixels[i] =pixels[i + 2];
pixels[i + 2] =temp;
}
encoder.SetPixelData(
BitmapPixelFormat.Rgba8,
BitmapAlphaMode.Straight,
(uint)src.PixelWidth,
(uint)src.PixelHeight,
96, // Horizontal DPI
96, // Vertical DPI
pixels
);
await encoder.FlushAsync();
}
catch (Exception e)
{
throw e;
}
}