c# - C#/UWP 中的屏幕截图
问题描述
我正在使用 UWP 桌面窗口应用程序,我正在尝试实现将屏幕截图保存到本地文件的功能,但我收到错误消息:
System.NullReferenceException:'对象引用未设置为对象的实例.
在等待 frame.SaveAsync(fileStream, CanvasBitmapFileFormat.Png, 1f); 在方法 SaveImageAsync 中。
你能告诉我出了什么问题吗?
namespace App5
{
public sealed partial class MainPage : Page
{
private SizeInt32 _lastSize;
private GraphicsCaptureItem _item;
private Direct3D11CaptureFramePool _framePool;
private GraphicsCaptureSession _session;
private CanvasDevice _canvasDevice;
private CompositionGraphicsDevice _compositionGraphicsDevice;
private Compositor _compositor;
private CompositionDrawingSurface _surface;
private CanvasBitmap _currentFrame;
private string _screenshotFilename = "test.png";
public MainPage()
{
this.InitializeComponent();
Setup();
}
private void Setup()
{
_canvasDevice = new CanvasDevice();
_compositionGraphicsDevice = CanvasComposition.CreateCompositionGraphicsDevice(
Window.Current.Compositor,
_canvasDevice);
_compositor = Window.Current.Compositor;
_surface = _compositionGraphicsDevice.CreateDrawingSurface(
new Size(400, 400),
DirectXPixelFormat.B8G8R8A8UIntNormalized,
DirectXAlphaMode.Premultiplied);
var visual = _compositor.CreateSpriteVisual();
visual.RelativeSizeAdjustment = Vector2.One;
var brush = _compositor.CreateSurfaceBrush(_surface);
brush.HorizontalAlignmentRatio = 0.5f;
brush.VerticalAlignmentRatio = 0.5f;
brush.Stretch = CompositionStretch.Uniform;
visual.Brush = brush;
ElementCompositionPreview.SetElementChildVisual(this, visual);
}
public async Task StartCaptureAsync()
{
var picker = new GraphicsCapturePicker();
GraphicsCaptureItem item = await picker.PickSingleItemAsync();
if (item != null)
{
StartCaptureInternal(item);
}
}
private void StartCaptureInternal(GraphicsCaptureItem item)
{
// Stop the previous capture if we had one.
StopCapture();
_item = item;
_lastSize = _item.Size;
_framePool = Direct3D11CaptureFramePool.Create(
_canvasDevice, // D3D device
DirectXPixelFormat.B8G8R8A8UIntNormalized, // Pixel format
2, // Number of frames
_item.Size); // Size of the buffers
_framePool.FrameArrived += (s, a) =>
{
using (var frame = _framePool.TryGetNextFrame())
{
ProcessFrame(frame);
}
};
_item.Closed += (s, a) =>
{
StopCapture();
};
_session = _framePool.CreateCaptureSession(_item);
_session.StartCapture();
}
public void StopCapture()
{
_session?.Dispose();
_framePool?.Dispose();
_item = null;
_session = null;
_framePool = null;
}
private void ProcessFrame(Direct3D11CaptureFrame frame)
{
bool needsReset = false;
bool recreateDevice = false;
if ((frame.ContentSize.Width != _lastSize.Width) ||
(frame.ContentSize.Height != _lastSize.Height))
{
needsReset = true;
_lastSize = frame.ContentSize;
}
try
{
CanvasBitmap canvasBitmap = CanvasBitmap.CreateFromDirect3D11Surface(
_canvasDevice,
frame.Surface);
_currentFrame = canvasBitmap;
FillSurfaceWithBitmap(canvasBitmap);
}
catch (Exception e) when (_canvasDevice.IsDeviceLost(e.HResult))
{
needsReset = true;
recreateDevice = true;
}
if (needsReset)
{
ResetFramePool(frame.ContentSize, recreateDevice);
}
}
private void FillSurfaceWithBitmap(CanvasBitmap canvasBitmap)
{
CanvasComposition.Resize(_surface, canvasBitmap.Size);
using (var session = CanvasComposition.CreateDrawingSession(_surface))
{
session.Clear(Colors.Transparent);
session.DrawImage(canvasBitmap);
}
}
private void ResetFramePool(SizeInt32 size, bool recreateDevice)
{
do
{
try
{
if (recreateDevice)
{
_canvasDevice = new CanvasDevice();
}
_framePool.Recreate(
_canvasDevice,
DirectXPixelFormat.B8G8R8A8UIntNormalized,
2,
size);
}
catch (Exception e) when (_canvasDevice.IsDeviceLost(e.HResult))
{
_canvasDevice = null;
recreateDevice = true;
}
} while (_canvasDevice == null);
}
private async void Button_ClickAsync(object sender, RoutedEventArgs e)
{
await StartCaptureAsync();
await SaveImageAsync(_screenshotFilename, _currentFrame);
}
private async Task SaveImageAsync(string filename, CanvasBitmap frame)
{
StorageFolder pictureFolder = KnownFolders.SavedPictures;
StorageFile file = await pictureFolder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
using (var fileStream = await file.OpenAsync(FileAccessMode.ReadWrite))
{
await frame.SaveAsync(fileStream, CanvasBitmapFileFormat.Png, 1f);
}
}
}
}
解决方案
此代码来自 Windows Forms .Net Core 项目,但我只是粘贴到 WPF 项目中,它可以工作。
在 WPF 中,您必须添加 Nuget 包 System.Drawing.Common:
您还必须添加对以下内容的引用:
using System.Windows.Forms;
using WindowsFormsIntegration;
using System.Drawing;
// take a screenshot
Bitmap bitmap = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
Graphics graphics = Graphics.FromImage(bitmap);
graphics.CopyFromScreen(0, 0, 0, 0, bitmap.Size);
// to save:
bitmap.Save(fileName);
上面的代码来自这个项目。我帮助某人创建子图像并在更大的图像中搜索子图像。他们有截图代码。
https://github.com/DataJuggler/SubImageCreator
该项目用于从较大的图像创建子图像并在较大的图像中搜索子图像。
推荐阅读
- python - 有没有办法解析 JSON 并使用 Python 获取此链接的请求
- swift - 创建一个带有换行符的 NSPredicate 作为字符串的一部分
- algorithm - 解决俄罗斯方块拼图
- python - Python 正则表达式匹配单词后的数字
- sas - SAS:错误 180-322 但它不是分号
- javascript - 如何测试从 Angular 组件字符串数组呈现的 [routerLink] 值?
- python - 在任务之间复制 contexvars.Context
- triggers - 是否可以向需要用户没有权限的触发器授予权限?
- laravel - 如何保持 laravel livewire 线:submit.prevent 重新加载页面
- android - 绑定应用程序提供程序时的Android ANR