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under the RenderSemanticsAnnotations#8187b subtree.
each child under this render object has BoxConstraints with both
minimum and maximum values. for example, RenderSemanticsAnnotations#a0a4b
uses BoxConstraints(0.0<=w<=800.0, 0.0<=h<=600.0).
all children of the RenderPhysicalShape#8e171 render object use
BoxConstraints(BoxConstraints(56.0<=w<=800.0, 28.0<=h<=600.0)).
the child RenderPadding#8455f sets a padding value of
EdgeInsets(8.0, 0.0, 8.0, 0.0).
this sets a left and right padding of 8 to all subsequent children of
this render object.
they now have new constraints:
BoxConstraints(40.0<=w<=784.0, 28.0<=h<=600.0).
this object, which the creator field tells us is
probably part of the TextButton’s definition,
sets a minimum width of 88 pixels on its contents and a
specific height of 36.0. this is the TextButton class implementing
the material design guidelines regarding button dimensions.
RenderPositionedBox#80b8d render object loosens the constraints again
to center the text within the button.
the RenderParagraph#59bc2 render object picks its size based on
its contents.
if you follow the sizes back up the tree,
you see how the size of the text influences the width of all the boxes
that form the button.
all parents take their child’s dimensions to size themselves.
another way to notice this is by looking at the relayoutBoundary
attribute of in the descriptions of each box.
this tells you how many ancestors depend on this element’s size.
for example, the innermost RenderPositionedBox line has a relayoutBoundary=up13.
this means that when flutter marks the RenderConstrainedBox as dirty,
it also marks box’s 13 ancestors as dirty because the new dimensions
might affect those ancestors.
to add information to the dump if you write your own render objects,
override debugFillProperties().
add DiagnosticsProperty objects to the method’s argument
then call the superclass method.
<topic_end>
<topic_start>
print the layer tree
to debug a compositing issue, use debugDumpLayerTree().
<topic_end>
<topic_start>
example 6: call debugDumpLayerTree()
<code_start>
import 'package:flutter/material.dart';
void main() {
runApp(
const MaterialApp(
home: AppHome(),
),
);
}
class AppHome extends StatelessWidget {
const AppHome({super.key});
@override
widget build(BuildContext context) {
return material(
child: center(
child: TextButton(
onPressed: () {
debugDumpLayerTree();
},
child: const Text('Dump layer tree'),
),
),
);
}
}
<code_end>
the RepaintBoundary widget creates:
a RenderRepaintBoundary RenderObject in the render tree
as shown in the example 5 results.
a new layer in the layer tree as shown in the example 6
results.
this reduces how much needs to be repainted.
<topic_end>
<topic_start>
print the focus tree
to debug a focus or shortcut issue, dump the focus tree
using the debugDumpFocusTree() function.
the debugDumpFocusTree() method returns the focus tree for the app.
the focus tree labels nodes in the following way:
if your app uses the focus widget, use the debugLabel
property to simplify finding its focus node in the tree.
you can also use the debugFocusChanges boolean property to enable
extensive logging when the focus changes.
<topic_end>
<topic_start>
example 7: call debugDumpFocusTree()
<code_start>
import 'package:flutter/material.dart';
void main() {
runApp(
const MaterialApp(
home: AppHome(),
),
);
}
class AppHome extends StatelessWidget {
const AppHome({super.key});