Windows 8 学习笔记（二十三）--WritableBitmap的读写操作C++

在开发中，涉及图片的处理经常需要用到WritableBitmap对象，这个对象可以直接作为数据源赋值给Image控件，但若要保存这个对象，我们只能将其序列化保存为一个图片文件，自然需要用到图片的编解码库：

将WritableBitmap保存为图片文件

WriteableBitmap^ wb =“您的源”；
IBuffer^ buffer = wb->PixelBuffer;
DataReader^ dataReader = DataReader::FromBuffer(buffer);
Array<unsigned char,1>^ fileContent =ref new Array<unsigned char,1>(buffer->Length);
dataReader->ReadBytes(fileContent);
task<StorageFile^>(ApplicationData::Current->LocalFolder->CreateFileAsync(pathName, CreationCollisionOption::ReplaceExisting)).then([this,fileContent,wb](StorageFile^ file)
{  
	task<IRandomAccessStream^>(file->OpenAsync(FileAccessMode::ReadWrite)).then([this,fileContent,wb](IRandomAccessStream^ _stream)
	{	
		task<BitmapEncoder^>(BitmapEncoder::CreateAsync(BitmapEncoder::JpegEncoderId,_stream)).then([this,fileContent,wb](BitmapEncoder^ encoder)
		{
	            encoder->SetPixelData(BitmapPixelFormat::Bgra8,BitmapAlphaMode::Straight,wb->PixelWidth ,wb->PixelHeight,96,96,fileContent);						
		    task<void>(encoder->FlushAsync()).then([=](void)
                    {
                      //Jpeg File Save Success!
                    });
                });
         });
});

 将图片文件读取到WritableBitmap对象

task<StorageFile^>  ReadTask(ApplicationData::Current->LocalFolder->GetFileAsync(filename));
ReadTask.then([=](StorageFile^ sampleFile)
{
	task<IRandomAccessStream^>(sampleFile->OpenAsync(FileAccessMode::Read)).then([=](IRandomAccessStream^ readStream)
	{					
	      int nWidth = 163;
	      int nHeigh = 202;
	      WriteableBitmap^ bitmapSnap = ref new WriteableBitmap(nWidth,nHeigh);	
	      readStream->Seek(0);
	     bitmapSnap->SetSource(readStream);
	});
});