Shift tap gesture (flutter#93835)

Author: justinmc

packages/flutter/lib/src/material/text_field.dart

@@ -86,33 +86,7 @@ class _TextFieldSelectionGestureDetectorBuilder extends TextSelectionGestureDete
   @override
   void onSingleTapUp(TapUpDetails details) {
     editableText.hideToolbar();
-    if (delegate.selectionEnabled) {
-      switch (Theme.of(_state.context).platform) {
-        case TargetPlatform.iOS:
-        case TargetPlatform.macOS:
-          switch (details.kind) {
-            case PointerDeviceKind.mouse:
-            case PointerDeviceKind.stylus:
-            case PointerDeviceKind.invertedStylus:
-              // Precise devices should place the cursor at a precise position.
-              renderEditable.selectPosition(cause: SelectionChangedCause.tap);
-              break;
-            case PointerDeviceKind.touch:
-            case PointerDeviceKind.unknown:
-              // On macOS/iOS/iPadOS a touch tap places the cursor at the edge
-              // of the word.
-              renderEditable.selectWordEdge(cause: SelectionChangedCause.tap);
-              break;
-          }
-          break;
-        case TargetPlatform.android:
-        case TargetPlatform.fuchsia:
-        case TargetPlatform.linux:
-        case TargetPlatform.windows:
-          renderEditable.selectPosition(cause: SelectionChangedCause.tap);
-          break;
-      }
-    }
+    super.onSingleTapUp(details);
     _state._requestKeyboard();
     _state.widget.onTap?.call();
   }

packages/flutter/lib/src/widgets/text_selection.dart

@@ -946,6 +946,65 @@ class TextSelectionGestureDetectorBuilder {
         && renderEditable.selection!.end >= textPosition.offset;
   }
 
+  // Expand the selection to the given global position.
+  //
+  // Either base or extent will be moved to the last tapped position, whichever
+  // is closest. The selection will never shrink or pivot, only grow.
+  //
+  // See also:
+  //
+  //   * [_extendSelection], which is similar but pivots the selection around
+  //     the base.
+  void _expandSelection(Offset offset, SelectionChangedCause cause) {
+    assert(cause != null);
+    assert(offset != null);
+    assert(renderEditable.selection?.baseOffset != null);
+
+    final TextPosition tappedPosition = renderEditable.getPositionForPoint(offset);
+    final TextSelection selection = renderEditable.selection!;
+    final bool baseIsCloser =
+        (tappedPosition.offset - selection.baseOffset).abs()
+        < (tappedPosition.offset - selection.extentOffset).abs();
+    final TextSelection nextSelection = selection.copyWith(
+      baseOffset: baseIsCloser ? selection.extentOffset : selection.baseOffset,
+      extentOffset: tappedPosition.offset,
+    );
+
+    editableText.userUpdateTextEditingValue(
+      editableText.textEditingValue.copyWith(
+        selection: nextSelection,
+      ),
+      cause,
+    );
+  }
+
+  // Extend the selection to the given global position.
+  //
+  // Holds the base in place and moves the extent.
+  //
+  // See also:
+  //
+  //   * [_expandSelection], which is similar but always increases the size of
+  //     the selection.
+  void _extendSelection(Offset offset, SelectionChangedCause cause) {
+    assert(cause != null);
+    assert(offset != null);
+    assert(renderEditable.selection?.baseOffset != null);
+
+    final TextPosition tappedPosition = renderEditable.getPositionForPoint(offset);
+    final TextSelection selection = renderEditable.selection!;
+    final TextSelection nextSelection = selection.copyWith(
+      extentOffset: tappedPosition.offset,
+    );
+
+    editableText.userUpdateTextEditingValue(
+      editableText.textEditingValue.copyWith(
+        selection: nextSelection,
+      ),
+      cause,
+    );
+  }
+
   /// Whether to show the selection toolbar.
   ///
   /// It is based on the signal source when a [onTapDown] is called. This getter
@@ -964,9 +1023,12 @@ class TextSelectionGestureDetectorBuilder {
   @protected
   RenderEditable get renderEditable => editableText.renderEditable;
 
-  /// The viewport offset pixels of the [RenderEditable] at the last drag start.
+  // The viewport offset pixels of the [RenderEditable] at the last drag start.
   double _dragStartViewportOffset = 0.0;
 
+  // True iff a tap + shift has been detected but the tap has not yet come up.
+  bool _isShiftTapping = false;
+
   /// Handler for [TextSelectionGestureDetector.onTapDown].
   ///
   /// By default, it forwards the tap to [RenderEditable.handleTapDown] and sets
@@ -986,6 +1048,28 @@ class TextSelectionGestureDetectorBuilder {
     _shouldShowSelectionToolbar = kind == null
       || kind == PointerDeviceKind.touch
       || kind == PointerDeviceKind.stylus;
+
+    // Handle shift + click selection if needed.
+    final bool isShiftPressed = HardwareKeyboard.instance.logicalKeysPressed
+        .any(<LogicalKeyboardKey>{
+          LogicalKeyboardKey.shiftLeft,
+          LogicalKeyboardKey.shiftRight,
+        }.contains);
+    if (isShiftPressed && renderEditable.selection?.baseOffset != null) {
+      _isShiftTapping = true;
+      switch (defaultTargetPlatform) {
+        case TargetPlatform.iOS:
+        case TargetPlatform.macOS:
+          _expandSelection(details.globalPosition, SelectionChangedCause.tap);
+          break;
+        case TargetPlatform.android:
+        case TargetPlatform.fuchsia:
+        case TargetPlatform.linux:
+        case TargetPlatform.windows:
+          _extendSelection(details.globalPosition, SelectionChangedCause.tap);
+          break;
+      }
+    }
   }
 
   /// Handler for [TextSelectionGestureDetector.onForcePressStart].
@@ -1043,8 +1127,37 @@ class TextSelectionGestureDetectorBuilder {
   ///    this callback.
   @protected
   void onSingleTapUp(TapUpDetails details) {
+    if (_isShiftTapping) {
+      _isShiftTapping = false;
+      return;
+    }
+
     if (delegate.selectionEnabled) {
-      renderEditable.selectWordEdge(cause: SelectionChangedCause.tap);
+      switch (defaultTargetPlatform) {
+        case TargetPlatform.iOS:
+        case TargetPlatform.macOS:
+          switch (details.kind) {
+            case PointerDeviceKind.mouse:
+            case PointerDeviceKind.stylus:
+            case PointerDeviceKind.invertedStylus:
+              // Precise devices should place the cursor at a precise position.
+              renderEditable.selectPosition(cause: SelectionChangedCause.tap);
+              break;
+            case PointerDeviceKind.touch:
+            case PointerDeviceKind.unknown:
+              // On macOS/iOS/iPadOS a touch tap places the cursor at the edge
+              // of the word.
+              renderEditable.selectWordEdge(cause: SelectionChangedCause.tap);
+              break;
+          }
+          break;
+        case TargetPlatform.android:
+        case TargetPlatform.fuchsia:
+        case TargetPlatform.linux:
+        case TargetPlatform.windows:
+          renderEditable.selectPosition(cause: SelectionChangedCause.tap);
+          break;
+      }
     }
   }