src/Tizen.NUI/src/public/Layouting/LayoutGroup.cs

   1 /*
   2  * Copyright (c) 2020 Samsung Electronics Co., Ltd.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  * http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  *
  16  */
  17 using System;
  18 using System.Collections.Generic;
  19 using System.ComponentModel;
  20 using System.Diagnostics;
  21 using Tizen.NUI.BaseComponents;
  22 using System.Linq;
  23 using Tizen.NUI.Binding.Internals;
  24 using static Tizen.NUI.Binding.BindableObject;
  25
  26 namespace Tizen.NUI
  27 {
  28     /// <summary>
  29     /// [Draft] LayoutGroup class providing container functionality.
  30     /// </summary>
  31     public class LayoutGroup : LayoutItem, ILayoutParent
  32     {
  33         /// <summary>
  34         /// [Draft] List of child layouts in this container.
  35         /// </summary>
  36         /// <since_tizen> 6 </since_tizen>
  37         protected List<LayoutItem> LayoutChildren{ get;} // Children of this LayoutGroup
  38
  39         /// <summary>
  40         /// [Draft] Constructor
  41         /// </summary>
  42         /// <since_tizen> 6 </since_tizen>
  43         public LayoutGroup()
  44         {
  45             LayoutChildren = new List<LayoutItem>();
  46         }
  47
  48         /// <summary>
  49         /// From ILayoutParent.<br />
  50         /// </summary>
  51         /// <since_tizen> 6 </since_tizen>
  52         /// <param name="childLayout">LayoutItem to add to the layout group.</param>
  53         public virtual void Add(LayoutItem childLayout)
  54         {
  55             LayoutChildren.Add(childLayout);
  56             childLayout.SetParent(this);
  57             // Child added to use a Add transition.
  58             childLayout.ConditionForAnimation = ConditionForAnimation | TransitionCondition.Add;
  59             // Child's parent sets all other children not being added to a ChangeOnAdd transition.
  60             SetConditionsForAnimationOnLayoutGroup(TransitionCondition.ChangeOnAdd);
  61             OnChildAdd(childLayout);
  62             RequestLayout();
  63         }
  64
  65         /// <summary>
  66         /// Remove all layout children.<br />
  67         /// </summary>
  68         /// <since_tizen> 6 </since_tizen>
  69         public void RemoveAll()
  70         {
  71             foreach( LayoutItem childLayout in LayoutChildren )
  72             {
  73                 childLayout.ConditionForAnimation = ConditionForAnimation | TransitionCondition.Remove;
  74                 childLayout.Owner = null;
  75             }
  76             LayoutChildren.Clear();
  77             // todo ensure child LayoutItems are still not parented to this group.
  78             RequestLayout();
  79         }
  80
  81         /// <summary>
  82         /// From ILayoutParent
  83         /// </summary>
  84         /// <param name="layoutItem">LayoutItem to remove from the layout group.</param>
  85         /// <since_tizen> 6 </since_tizen>
  86         public virtual void Remove(LayoutItem layoutItem)
  87         {
  88             bool childRemoved = false;
  89             foreach( LayoutItem childLayout in LayoutChildren.ToList() )
  90             {
  91                 if( childLayout == layoutItem )
  92                 {
  93                     childLayout.ClearReplaceFlag();
  94                     LayoutChildren.Remove(childLayout);
  95
  96                     if (LayoutWithTransition)
  97                     {
  98                         if (!childLayout.IsReplaceFlag())
  99                         {
 100                             NUIApplication.GetDefaultWindow().LayoutController.AddToRemovalStack(childLayout);
 101                         }
 102
 103                         childLayout.ConditionForAnimation = childLayout.ConditionForAnimation | TransitionCondition.Remove;
 104                         // Add LayoutItem to the transition stack so can animate it out.
 105                         NUIApplication.GetDefaultWindow().LayoutController.AddTransitionDataEntry(new LayoutData(layoutItem, ConditionForAnimation, 0, 0, 0, 0));
 106                     }
 107
 108                     // Reset condition for animation ready for next transition when required.
 109                     // SetFrame usually would do this but this LayoutItem is being removed.
 110                     childLayout.ConditionForAnimation = TransitionCondition.Unspecified;
 111                     childRemoved = true;
 112
 113                     break;
 114                 }
 115             }
 116
 117             if (childRemoved)
 118             {
 119                 // If child removed then set all siblings not being added to a ChangeOnRemove transition.
 120                 SetConditionsForAnimationOnLayoutGroup(TransitionCondition.ChangeOnRemove);
 121             }
 122
 123             RequestLayout();
 124         }
 125
 126
 127         /// <summary>
 128         /// Sets the sibling order of the layout item so the layout can be defined within the same parent.
 129         /// </summary>
 130         /// <param name="order">the sibling order of the layout item</param>
 131         /// <since_tizen> 6 </since_tizen>
 132         /// This will be public opened in tizen_next after ACR done. Before ACR, need to be hidden as inhouse API.
 133         [EditorBrowsable(EditorBrowsableState.Never)]
 134         public void ChangeLayoutSiblingOrder(int order)
 135         {
 136             if(Owner != null && Owner.Parent != null)
 137             {
 138                 LayoutGroup parent = Owner.Parent.Layout as LayoutGroup;
 139
 140                 if(parent != null && parent.LayoutChildren.Count>order)
 141                 {
 142                     parent.LayoutChildren.Remove(this);
 143                     parent.LayoutChildren.Insert(order,this);
 144                 }
 145             }
 146
 147             RequestLayout();
 148         }
 149
 150         // Attaches to View ChildAdded signal so called when a View is added to a view.
 151         private void AddChildToLayoutGroup(View child)
 152         {
 153             // Only give children a layout if their parent is an explicit container or a pure View.
 154             // Pure View meaning not derived from a View, e.g a Legacy container.
 155             // layoutSet flag is true when the View became a layout using the set Layout API opposed to automatically due to it's parent.
 156             // First time the set Layout API is used by any View the Window no longer has layoutingDisabled.
 157
 158             // If child already has a Layout then don't change it.
 159             if (! View.layoutingDisabled && (null == child.Layout))
 160             {
 161                 // Only wrap View with a Layout if a child a pure View or Layout explicitly set on this Layout
 162                 if ((true == Owner.layoutSet || GetType() == typeof(View)))
 163                 {
 164                     // If child of this layout is a pure View then assign it a LayoutGroup
 165                     // If the child is derived from a View then it may be a legacy or existing container hence will do layouting itself.
 166                     child.Layout = new AbsoluteLayout();
 167                 }
 168             }
 169             else
 170             {
 171                 // Add child layout to this LayoutGroup (Setting parent in the process)
 172                 if(child.Layout != null)
 173                 {
 174                     Add(child.Layout);
 175                 }
 176             }
 177             // Parent transitions are not attached to children.
 178         }
 179
 180         /// <summary>
 181         /// If the child has a layout then it is removed from the parent layout.
 182         /// </summary>
 183         /// <param name="child">Child View to remove.</param>
 184         internal void RemoveChildFromLayoutGroup(View child)
 185         {
 186             Debug.Assert(child.Layout !=null);
 187             Remove(child.Layout);
 188         }
 189
 190         /// <summary>
 191         /// Set all children in a LayoutGroup to the supplied condition.
 192         /// Children with Add or Remove conditions should not be changed.
 193         /// </summary>
 194         private void SetConditionsForAnimationOnLayoutGroup( TransitionCondition conditionToSet)
 195         {
 196             foreach( LayoutItem childLayout in LayoutChildren )
 197             {
 198                 switch( conditionToSet )
 199                 {
 200                 case TransitionCondition.ChangeOnAdd :
 201                 {
 202                     // If other children also being added (TransitionCondition.Add) then do not change their
 203                     // conditions, Continue to use their Add transitions.
 204                     if (childLayout.ConditionForAnimation.HasFlag(TransitionCondition.Add))
 205                     {
 206                         break;  // Child being Added so don't update it's condition
 207                     }
 208                     else
 209                     {
 210                         // Set siblings for the child being added to use the ChangeOnAdd transition.
 211                         childLayout.ConditionForAnimation = TransitionCondition.ChangeOnAdd;
 212                     }
 213                     break;
 214                 }
 215                 case TransitionCondition.ChangeOnRemove :
 216                 {
 217                     if (childLayout.ConditionForAnimation.HasFlag(TransitionCondition.Remove))
 218                     {
 219                         break; // Child being Removed so don't update it's condition
 220                     }
 221                     else
 222                     {
 223                         childLayout.ConditionForAnimation = TransitionCondition.ChangeOnRemove;
 224                     }
 225                     break;
 226                 }
 227                 case TransitionCondition.LayoutChanged :
 228                 {
 229                     childLayout.ConditionForAnimation = TransitionCondition.LayoutChanged;
 230                     break;
 231                 }
 232                 }
 233             }
 234
 235         }
 236
 237         /// <summary>
 238         /// Callback for View.ChildAdded event
 239         /// </summary>
 240         /// <param name="sender">The object triggering the event.</param>
 241         /// <param name="childAddedEvent">Arguments from the event.</param>
 242         void OnChildAddedToOwner(object sender, View.ChildAddedEventArgs childAddedEvent)
 243         {
 244             AddChildToLayoutGroup(childAddedEvent.Added);
 245         }
 246
 247         /// <summary>
 248         /// Callback for View.ChildRemoved event
 249         /// </summary>
 250         /// <param name="sender">The object triggering the event.</param>
 251         /// <param name="childRemovedEvent">Arguments from the event.</param>
 252         void OnChildRemovedFromOwner(object sender, View.ChildRemovedEventArgs childRemovedEvent)
 253         {
 254             RemoveChildFromLayoutGroup(childRemovedEvent.Removed);
 255         }
 256
 257         /// <summary>
 258         /// Calculate the right measure spec for this child.
 259         /// Does the hard part of MeasureChildren: figuring out the MeasureSpec to
 260         /// pass to a particular child. This method figures out the right MeasureSpec
 261         /// for one dimension (height or width) of one child view.<br />
 262         /// </summary>
 263         /// <param name="parentMeasureSpec">The requirements for this view. MeasureSpecification.</param>
 264         /// <param name="padding">The padding of this view for the current dimension and margins, if applicable. LayoutLength.</param>
 265         /// <param name="childDimension"> How big the child wants to be in the current dimension. LayoutLength.</param>
 266         /// <returns>a MeasureSpec for the child.</returns>
 267         public static MeasureSpecification GetChildMeasureSpecification(MeasureSpecification parentMeasureSpec, LayoutLength padding, LayoutLength childDimension)
 268         {
 269             MeasureSpecification.ModeType specMode = parentMeasureSpec.Mode;
 270             MeasureSpecification.ModeType resultMode = MeasureSpecification.ModeType.Unspecified;
 271
 272             // Child only can use parent's size without parent's padding and own margin.
 273             LayoutLength resultSize = new LayoutLength(Math.Max( 0.0f, (parentMeasureSpec.Size - padding).AsDecimal()));
 274             switch( specMode )
 275             {
 276                 // Parent has imposed an exact size on us
 277                 case MeasureSpecification.ModeType.Exactly:
 278                 {
 279                     if ((int)childDimension.AsRoundedValue() == LayoutParamPolicies.MatchParent)
 280                     {
 281                         resultMode = MeasureSpecification.ModeType.Exactly;
 282                     }
 283                     else if ((int)childDimension.AsRoundedValue() == LayoutParamPolicies.WrapContent)
 284                     {
 285                         resultMode = MeasureSpecification.ModeType.AtMost;
 286                     }
 287                     else
 288                     {
 289                         resultSize = childDimension;
 290                         resultMode = MeasureSpecification.ModeType.Exactly;
 291                     }
 292
 293                     break;
 294                 }
 295
 296                 // Parent has imposed a maximum size on us
 297                 case MeasureSpecification.ModeType.AtMost:
 298                 {
 299                     if (childDimension.AsRoundedValue() == LayoutParamPolicies.MatchParent)
 300                     {
 301                         // Crashed. Cannot calculate.
 302
 303                         // Child wants to be our size, but our size is not fixed.
 304                         // Constrain child to not be bigger than us.
 305                         resultMode = MeasureSpecification.ModeType.AtMost;
 306                     }
 307                     else if (childDimension.AsRoundedValue() == LayoutParamPolicies.WrapContent)
 308                     {
 309                         // Child wants to determine its own size. It can't be
 310                         // bigger than us.
 311
 312                         // Don't need parent's size. Size of this child will be determined by its children.
 313                         resultMode = MeasureSpecification.ModeType.AtMost;
 314                     }
 315                     else
 316                     {
 317                         // Child wants a specific size... so be it
 318                         resultSize = childDimension;
 319                         resultMode = MeasureSpecification.ModeType.Exactly;
 320                     }
 321
 322                     break;
 323                 }
 324
 325                 // Parent asked to see how big we want to be
 326                 case MeasureSpecification.ModeType.Unspecified:
 327                 {
 328                     if ((childDimension.AsRoundedValue() == LayoutParamPolicies.MatchParent))
 329                     {
 330                         // Child wants to be our size... find out how big it should be
 331
 332                         // There is no one who has exact size in parent hierarchy.
 333                         // Cannot calculate.
 334                         resultMode = MeasureSpecification.ModeType.Unspecified;
 335                     }
 336                     else if (childDimension.AsRoundedValue() == (LayoutParamPolicies.WrapContent))
 337                     {
 338                         // Child wants to determine its own size.... find out how big
 339                         // it should be
 340                         resultMode = MeasureSpecification.ModeType.Unspecified;
 341                     }
 342                     else
 343                     {
 344                         // Child wants a specific size... let him have it
 345                         resultSize = childDimension;
 346                         resultMode = MeasureSpecification.ModeType.Exactly;
 347                     }
 348                     break;
 349                 }
 350             } // switch
 351
 352             return new MeasureSpecification( resultSize, resultMode );
 353         }
 354
 355         /// <summary>
 356         /// Measure the layout and its content to determine the measured width and the measured height.<br />
 357         /// If this method is overridden, it is the subclass's responsibility to make
 358         /// sure the measured height and width are at least the layout's minimum height
 359         /// and width. <br />
 360         /// </summary>
 361         /// <param name="widthMeasureSpec">horizontal space requirements as imposed by the parent.</param>
 362         /// <param name="heightMeasureSpec">vertical space requirements as imposed by the parent.</param>
 363         /// <since_tizen> 6 </since_tizen>
 364         protected override void OnMeasure(MeasureSpecification widthMeasureSpec, MeasureSpecification heightMeasureSpec)
 365         {
 366             LayoutLength measuredWidth = new LayoutLength(0.0f);
 367             LayoutLength measuredHeight = new LayoutLength(0.0f);
 368
 369             // Layout takes size of largest child width and largest child height dimensions
 370             foreach( LayoutItem childLayout in LayoutChildren )
 371             {
 372                 if( childLayout != null )
 373                 {
 374                     MeasureChildWithMargins( childLayout, widthMeasureSpec, new LayoutLength(0), heightMeasureSpec, new LayoutLength(0) );
 375                     LayoutLength childWidth = new LayoutLength(childLayout.MeasuredWidth.Size);
 376                     LayoutLength childHeight = new LayoutLength( childLayout.MeasuredHeight.Size);
 377
 378                     Extents childMargin = childLayout.Margin;
 379                     measuredWidth = new LayoutLength(Math.Max( measuredWidth.AsDecimal(), childWidth.AsDecimal() + childMargin.Start + childMargin.End));
 380                     measuredHeight = new LayoutLength(Math.Max( measuredHeight.AsDecimal(), childHeight.AsDecimal() + childMargin.Top + childMargin.Bottom));
 381                 }
 382             }
 383
 384             if( 0 == LayoutChildren.Count )
 385             {
 386                 // Must be a leaf as has no children
 387                 measuredWidth = GetDefaultSize( SuggestedMinimumWidth, widthMeasureSpec );
 388                 measuredHeight = GetDefaultSize( SuggestedMinimumHeight, heightMeasureSpec );
 389             }
 390
 391             SetMeasuredDimensions( new MeasuredSize( measuredWidth, MeasuredSize.StateType.MeasuredSizeOK ),
 392                                    new MeasuredSize( measuredHeight, MeasuredSize.StateType.MeasuredSizeOK ) );
 393         }
 394
 395         /// <summary>
 396         /// Called from Layout() when this layout should assign a size and position to each of its children.<br />
 397         /// Derived classes with children should override this method and call Layout() on each of their children.<br />
 398         /// </summary>
 399         /// <param name="changed">This is a new size or position for this layout.</param>
 400         /// <param name="left">Left position, relative to parent.</param>
 401         /// <param name="top"> Top position, relative to parent.</param>
 402         /// <param name="right">Right position, relative to parent.</param>
 403         /// <param name="bottom">Bottom position, relative to parent.</param>
 404         /// <since_tizen> 6 </since_tizen>
 405         protected override void OnLayout(bool changed, LayoutLength left, LayoutLength top, LayoutLength right, LayoutLength bottom)
 406         {
 407             foreach( LayoutItem childLayout in LayoutChildren )
 408             {
 409                 if( childLayout !=null )
 410                 {
 411                     // Use position if explicitly set to child otherwise will be top left.
 412                     var childLeft = new LayoutLength( childLayout.Owner.Position2D.X );
 413                     var childTop = new LayoutLength( childLayout.Owner.Position2D.Y );
 414
 415                     View owner = Owner;
 416
 417                     if ( owner )
 418                     {
 419                         // Margin and Padding only supported when child anchor point is TOP_LEFT.
 420                         if ( owner.PivotPoint == PivotPoint.TopLeft || ( owner.PositionUsesPivotPoint == false ) )
 421                         {
 422                             childLeft = childLeft + owner.Padding.Start + childLayout.Margin.Start;
 423                             childTop = childTop + owner.Padding.Top + childLayout.Margin.Top;
 424                         }
 425                     }
 426                     childLayout.Layout( childLeft, childTop, childLeft + childLayout.MeasuredWidth.Size, childTop + childLayout.MeasuredHeight.Size );
 427                 }
 428             }
 429         }
 430
 431         /// <summary>
 432         /// Overridden method called when the layout is attached to an owner.<br />
 433         /// </summary>
 434         /// <since_tizen> 6 </since_tizen>
 435         protected override void OnAttachedToOwner()
 436         {
 437             // Layout takes ownership of it's owner's children.
 438             foreach (View view in Owner.Children)
 439             {
 440                 AddChildToLayoutGroup(view);
 441             }
 442
 443             // Connect to owner ChildAdded signal.
 444             Owner.ChildAdded += OnChildAddedToOwner;
 445
 446             // Removing Child from the owners View will directly call the LayoutGroup removal API.
 447         }
 448
 449         /// <summary>
 450         /// Virtual method to allow derived classes to remove any children before it is removed from
 451         /// its parent.
 452         /// </summary>
 453         [EditorBrowsable(EditorBrowsableState.Never)]
 454         protected override void OnUnparent()
 455         {
 456             // Disconnect to owner ChildAdded signal.
 457             Owner.ChildAdded -= OnChildAddedToOwner;
 458         }
 459
 460         // Virtual Methods that can be overridden by derived classes.
 461
 462         /// <summary>
 463         /// Callback when child is added to container.<br />
 464         /// Derived classes can use this to set their own child properties on the child layout's owner.<br />
 465         /// </summary>
 466         /// <param name="child">The Layout child.</param>
 467         /// <since_tizen> 6 </since_tizen>
 468         protected virtual void OnChildAdd(LayoutItem child)
 469         {
 470         }
 471
 472         /// <summary>
 473         /// Callback when child is removed from container.<br />
 474         /// </summary>
 475         /// <param name="child">The Layout child.</param>
 476         /// <since_tizen> 6 </since_tizen>
 477         protected virtual void OnChildRemove(LayoutItem child)
 478         {
 479         }
 480
 481         /// <summary>
 482         /// Ask all of the children of this view to measure themselves, taking into
 483         /// account both the MeasureSpec requirements for this view and its padding.<br />
 484         /// The heavy lifting is done in GetChildMeasureSpec.<br />
 485         /// </summary>
 486         /// <param name="widthMeasureSpec">The width requirements for this view.</param>
 487         /// <param name="heightMeasureSpec">The height requirements for this view.</param>
 488         /// <since_tizen> 6 </since_tizen>
 489         protected virtual void MeasureChildren(MeasureSpecification widthMeasureSpec, MeasureSpecification heightMeasureSpec)
 490         {
 491             foreach( LayoutItem childLayout in LayoutChildren )
 492             {
 493                 MeasureChildWithMargins(childLayout, widthMeasureSpec, new LayoutLength(0), heightMeasureSpec, new LayoutLength(0));
 494             }
 495         }
 496
 497         /// <summary>
 498         /// Ask one of the children of this view to measure itself, taking into
 499         /// account both the MeasureSpec requirements for this view and its padding.<br />
 500         /// The heavy lifting is done in GetChildMeasureSpecification.<br />
 501         /// </summary>
 502         /// <param name="child">The child to measure.</param>
 503         /// <param name="parentWidthMeasureSpec">The width requirements for this view.</param>
 504         /// <param name="parentHeightMeasureSpec">The height requirements for this view.</param>
 505         /// <since_tizen> 6 </since_tizen>
 506         protected virtual void MeasureChild(LayoutItem child, MeasureSpecification parentWidthMeasureSpec, MeasureSpecification parentHeightMeasureSpec)
 507         {
 508             View childOwner = child.Owner;
 509
 510             MeasureSpecification childWidthMeasureSpec = GetChildMeasureSpecification(
 511                         new MeasureSpecification(new LayoutLength(parentWidthMeasureSpec.Size), parentWidthMeasureSpec.Mode),
 512                         new LayoutLength(Padding.Start + Padding.End ),
 513                         new LayoutLength(childOwner.WidthSpecification) );
 514
 515             MeasureSpecification childHeightMeasureSpec = GetChildMeasureSpecification(
 516                         new MeasureSpecification(new LayoutLength(parentHeightMeasureSpec.Size), parentHeightMeasureSpec.Mode),
 517                         new LayoutLength(Padding.Top + Padding.Bottom),
 518                         new LayoutLength(childOwner.HeightSpecification));
 519
 520             child.Measure(childWidthMeasureSpec, childHeightMeasureSpec);
 521         }
 522
 523         /// <summary>
 524         /// Ask one of the children of this view to measure itself, taking into
 525         /// account both the MeasureSpec requirements for this view and its padding.<br />
 526         /// and margins. The heavy lifting is done in GetChildMeasureSpecification.<br />
 527         /// </summary>
 528         /// <param name="child">The child to measure.</param>
 529         /// <param name="parentWidthMeasureSpec">The width requirements for this view.</param>
 530         /// <param name="widthUsed">Extra space that has been used up by the parent horizontally (possibly by other children of the parent).</param>
 531         /// <param name="parentHeightMeasureSpec">The height requirements for this view.</param>
 532         /// <param name="heightUsed">Extra space that has been used up by the parent vertically (possibly by other children of the parent).</param>
 533         /// <since_tizen> 6 </since_tizen>
 534         protected virtual void MeasureChildWithMargins(LayoutItem child, MeasureSpecification parentWidthMeasureSpec, LayoutLength widthUsed, MeasureSpecification parentHeightMeasureSpec, LayoutLength heightUsed)
 535         {
 536             View childOwner = child.Owner;
 537
 538
 539             MeasureSpecification childWidthMeasureSpec = GetChildMeasureSpecification(
 540                         new MeasureSpecification(
 541                             new LayoutLength(parentWidthMeasureSpec.Size + widthUsed - (childOwner.Margin.Start + childOwner.Margin.End)),
 542                             parentWidthMeasureSpec.Mode),
 543                         new LayoutLength(Padding.Start + Padding.End ),
 544                         new LayoutLength(childOwner.WidthSpecification) );
 545
 546             MeasureSpecification childHeightMeasureSpec = GetChildMeasureSpecification(
 547                         new MeasureSpecification(
 548                             new LayoutLength(parentHeightMeasureSpec.Size + heightUsed - (childOwner.Margin.Top + childOwner.Margin.Bottom)),
 549                             parentHeightMeasureSpec.Mode),
 550                         new LayoutLength(Padding.Top + Padding.Bottom),
 551                         new LayoutLength(childOwner.HeightSpecification));
 552             child.Measure( childWidthMeasureSpec, childHeightMeasureSpec );
 553
 554         }
 555
 556         /// <summary>
 557         /// Gets the value that is contained in the attached BindableProperty.
 558         /// </summary>
 559         /// <typeparam name="T">The return type of property</typeparam>
 560         /// <param name="bindable">The bindable object.</param>
 561         /// <param name="property">The BindableProperty for which to get the value.</param>
 562         /// <returns>The value that is contained in the attached BindableProperty.</returns>
 563         [EditorBrowsable(EditorBrowsableState.Never)]
 564         public static T GetAttachedValue<T>(Binding.BindableObject bindable, Binding.BindableProperty property)
 565         {
 566             if (bindable == null)
 567                 throw new ArgumentNullException(nameof(bindable));
 568
 569             return (T)bindable.GetValue(property);
 570         }
 571
 572         /// <summary>
 573         /// Sets the value of the attached property.
 574         /// </summary>
 575         /// <param name="bindable">The bindable object.</param>
 576         /// <param name="property">The BindableProperty on which to assign a value.</param>
 577         /// <param name="value">The value to set.</param>
 578         [EditorBrowsable(EditorBrowsableState.Never)]
 579         public static void SetAttachedValue(Binding.BindableObject bindable, Binding.BindableProperty property, object value)
 580         {
 581             if (bindable == null)
 582                 throw new ArgumentNullException(nameof(bindable));
 583
 584             bindable.SetValueCore(property, value, SetValueFlags.None, SetValuePrivateFlags.ManuallySet, false);
 585         }
 586         internal static void OnChildPropertyChanged(Binding.BindableObject bindable, object oldValue, object newValue)
 587         {
 588             View view = bindable as View;
 589             view?.Layout?.RequestLayout();
 590         }
 591     }
 592 }