[UWP] Implement clipboard.

shell/platform/windows/platform_handler_winuwp.cc

@@ -4,7 +4,14 @@
 
 #include "flutter/shell/platform/windows/platform_handler_winuwp.h"
 
+#include "third_party/cppwinrt/generated/winrt/Windows.ApplicationModel.DataTransfer.h"
+#include "third_party/cppwinrt/generated/winrt/Windows.Foundation.h"
+#include "third_party/cppwinrt/generated/winrt/Windows.UI.Core.h"
+
 #include "flutter/shell/platform/windows/flutter_windows_view.h"
+#include "flutter/shell/platform/windows/string_conversion.h"
+
+static constexpr char kValueKey[] = "value";
 
 namespace flutter {
 
@@ -21,24 +28,84 @@ PlatformHandlerWinUwp::PlatformHandlerWinUwp(BinaryMessenger* messenger,
 
 PlatformHandlerWinUwp::~PlatformHandlerWinUwp() = default;
 
+bool isWindowInForeground() {
+  auto activation_mode =
+      winrt::Windows::UI::Core::CoreWindow::GetForCurrentThread()
+          .ActivationMode();
+  return activation_mode == winrt::Windows::UI::Core::CoreWindowActivationMode::
+                                ActivatedInForeground;
+}
+
 void PlatformHandlerWinUwp::GetPlainText(
     std::unique_ptr<MethodResult<rapidjson::Document>> result,
     std::string_view key) {
-  // TODO: Implement. See https://github.com/flutter/flutter/issues/70214.
-  result->NotImplemented();
+  // We call `Clipboard::GetContent()` when the application window is in
+  // focus, otherwise calling this will throw an error.
+  if (!isWindowInForeground()) {
+    result->Error(kClipboardError,
+                  "Unable to read clipboard. The window is not focused.");
+    return;
+  }
+
+  auto content =
+      winrt::Windows::ApplicationModel::DataTransfer::Clipboard::GetContent();
+
+  // Calling `DataPackageView::GetTextAsync()` when the clipboard has no text
+  // content will throw an error.
+  if (!content.Contains(winrt::Windows::ApplicationModel::DataTransfer::
+                            StandardDataFormats::Text())) {
+    result->Success(rapidjson::Document());
+    return;
+  }
+
+  // Waiting `DataPackageView::GetTextAsync()` using `TResult.get()` on the
+  // platform thread will causes the application stop, so we continue
+  // response on this callback.
+  content.GetTextAsync().Completed(
+      [result = std::move(result), key](auto async_info, auto _async_status) {
+        auto clipboard_string = async_info.GetResults();
+
+        rapidjson::Document document;
+        document.SetObject();
+        rapidjson::Document::AllocatorType& allocator = document.GetAllocator();
+        document.AddMember(
+            rapidjson::Value(key.data(), allocator),
+            rapidjson::Value(Utf8FromUtf16(clipboard_string), allocator),
+            allocator);
+        result->Success(document);
+      });
 }
 
 void PlatformHandlerWinUwp::GetHasStrings(
     std::unique_ptr<MethodResult<rapidjson::Document>> result) {
-  // TODO: Implement. See https://github.com/flutter/flutter/issues/70214.
-  result->NotImplemented();
+  bool has_string = false;
+
+  // We call `Clipboard::GetContent()` when the application window is in
+  // focus, otherwise calling this will throw an error.
+  if (isWindowInForeground()) {
+    has_string =
+        winrt::Windows::ApplicationModel::DataTransfer::Clipboard::GetContent()
+            .Contains(winrt::Windows::ApplicationModel::DataTransfer::
+                          StandardDataFormats::Text());
+  }
+
+  rapidjson::Document document;
+  document.SetObject();
+  rapidjson::Document::AllocatorType& allocator = document.GetAllocator();
+  document.AddMember(rapidjson::Value(kValueKey, allocator),
+                     rapidjson::Value(has_string), allocator);
+  result->Success(document);
 }
 
 void PlatformHandlerWinUwp::SetPlainText(
     const std::string& text,
     std::unique_ptr<MethodResult<rapidjson::Document>> result) {
-  // TODO: Implement. See https://github.com/flutter/flutter/issues/70214.
-  result->NotImplemented();
+  winrt::Windows::ApplicationModel::DataTransfer::DataPackage content;
+  content.SetText(Utf16FromUtf8(text));
+  winrt::Windows::ApplicationModel::DataTransfer::Clipboard::SetContent(
+      content);
+
+  result->Success();
 }
 
 }  // namespace flutter