Sorry if this is a dup, I see a lot of questions regarding text wrapping, but not generic widget wrapping in a row.
I have a dynamic row of buttons within a row. I'd like to wrap the buttons to create a second row if the list becomes longer than the width of the screen. Is it possible to do this automatically, or do I need to manually detect and create the correct number of rows.
If the latter, does anybody have pointers to measuring a widget's width vs screen width? Right now I'm doing something like:
...
return Row(
children: List.generate(count*2 + 1, (i) {
if (i %2 == 0) {
return Spacer();
}
return RaisedButton(child: Text((i / 2).round().toString(), onPressed: (){...});
});
Row is useful when you need to organize child widgets in a single line. Wrap with default direction is an alternative to Row that moves child widgets to the next line if there is no enough space
Related
I need to get the whole list.builder height including the part that is out of the screen view
The List children vary in height
i used the GlobalKey method but it is giving me only the height of the list shown in the screen
I found this solution and it's working and give me the full list.builder height after scrolling event
but when adding more children to the list.builder by changing the state
this code doesn't work anymore
scrollController.addListener(() {
double? fullListViewHeight;
double fullListHeightHelper = listKey.currentContext!.size!.height +
scrollController.position.extentAfter;
fullListView ??= fullListHeightHelper;
}
listview.builder only build the item that shown to user, in order to get the height with GlobalKey method, you can use listView which build all item at the same time. If you don't know how pass your list to listView , see this example:
List yourList = [...];
_buildList(){
List<Widget> _children =yourList.map((e) => YourListItem()).toList();
return ListView(
key:yourKey,
children: _children,
);
}
it is giving me only the height of the list shown in the screen
yes.. thats correct. because listview not render all the children. see the documentation of listview:
The ListView.builder ...constructor is appropriate for list views with
a large (or infinite) number of children because the builder is called
only for those children that are actually visible.
to get exact height of all children is impossible. since when the widget child is scrolled out of view, the associated element subtree, states and render objects are destroyed.
I think you need to calculate it manually or make the children height is same for all.
To calculate it, you need to make each item the same height. Then,
To get the height of the ListView.builder you simply multiply the height of each item by the length of the ListView.builder.
I am building a quiz app using Dart flutter in that some questions will get displayed and users have to click on true or false buttons depending upon question is right or wrong. To tell users that they are right or wrong icon (✓ or ✘) will get displayed in bottom row every time they choose answer by clicking on either of the button. But in flutter if row gets completely filled i got error
value: Not in inclusive range. So i want that icon should automatically go to next row.
Heres the short code which i tried:
List scorekeeper = [];
void score(bool userpickedanswer) {
setState((){
if (userpickedanswer == correctanswer) {
scorekeeper.add(Icon(Icons.check, color: Colors.green,));
}
else {
scorekeeper.add(Icon(Icons.close, color: Colors.red,));
}
}
Row {
childeren : scorekeeper
You can use the Wrap widget instead of the Row widget and when the line of icon fills to the end the Wrap widget makes another line automatically
Use the code like this:
Wrap(
children: scorekeeper,
),
You can use a wrap instead of a row. It prevents overflow by displaying the items depending on the available space:
https://api.flutter.dev/flutter/widgets/Wrap-class.html
//SOLVED: one of the containers inside the stack had an margin attribute that margins symetrically. Changed it to EdgeInsets.only(left:..,top:..)
I want to let my ListView start after the blue part of my page. But there is an blank and redundant space that doesn't allow me to start at expected point.
the blank space that i get
Here is my code:
Column(children:[Stack(some other code),Expanded(child:ListView(..))]);
The space is there because you have wrapped Stack(some other code) inside Column.
This is what you should do if you want the ListView to be over some other code,
Stack(
children:[
//some other code,
Column(
children:[
Expanded(
child : ListView(...)
),
...
According to documentation:
By default, ListView will automatically pad the list's scrollable extremities to avoid partial obstructions indicated by MediaQuery's padding. To avoid this behavior, override with a zero padding property.
To remove it wrap the ListView into a MediaQuery.removePadding:
MediaQuery.removePadding(
context: context,
removeTop: true,
child: ListView(...))
I am running into a problem where I am wanting to remove the space between expansion panels of an expansion panel list when the panels are expanded.
Images of unwanted behavior, these images are taken from flutter documentation:
List when not expanded, which is fine:
List when expanded:
- You can see the gap between the sections. This is what I do not want for my app.
Any tips are appreciated.
Try Modifying The Actual Implementations
If you have some prior programming experience, this should make sense...
Find these files:
expansion_panel.dart
expansion_title.dart
expand_icon.dart
mergeable_material.dart
These files should be located in the External Library > Dart Packages > Flutter > src > material. Note that the material folder may be expressed as "src.material".
Android Studio should allow you to hover over the ExpansionPanel Widget and right-click it. After right-clicking it you should see a list of shortcuts, one being "Go to". Click on the "Go to" option which should bring up more options, one of which being "Implementation(s)". This should bring you to where you need. According to my version, double clicking the widget name so the entire widget's name is highlighted should allow for a keyboard shortcut Ctrl+Alt+B.
The key file you must go into is "mergeable_material.dart". In "mergeable.dart", go to the MaterialGap constructor:
const MaterialGap({
#required LocalKey key,
this.size = 16.0,
//This is the size of the gap between ExpansionTiles WHEN EXPANDED
}) : assert(key != null),
super(key);
This size variable controls the gap between the Expansion Tiles ONLY when EXPANDED. Setting "this.size = 0.0" should remove the gap.
If you want to know why this is, long story short, when the ExpansionPanels list of widgets property is being defined (which is in expansion_panel.dart) a "MaterialGap" is being added between the children. We modified the material gap to be 0.0 thus effectively removing the gap.
Other things you can do:
Change the Trailing Icon in the Header.
Go to expand.dart file. Go to the bottom of the file where the build method should be. In the return statement, replace the icon button with 'whatever' you want (within reason).
#override
Widget build(BuildContext context) {
assert(debugCheckHasMaterial(context));
assert(debugCheckHasMaterialLocalizations(context));
final MaterialLocalizations localizations = MaterialLocalizations.of(context);
final String onTapHint = widget.isExpanded ? localizations.expandedIconTapHint :
localizations.collapsedIconTapHint;
return Semantics(
onTapHint: widget.onPressed == null ? null : onTapHint,
child: Container() //Replaced the Icon Button here to remove it
);
}
Keep in mind that without a button, you must make canTapOnHeader: true, or you won't
be able to expand the panel. You can make sure you don't forget to do this by going
to the ExpansionPanel constructor and changing "this.canTapOnHeader = false;" to
"this.canTapOnHeader = true;
ExpansionPanel({
#required this.headerBuilder,
#required this.body,
this.isExpanded = false,
this.canTapOnHeader = true, //Changed this to true from false
}) : assert(headerBuilder != null),
assert(body != null),
assert(isExpanded != null),
assert(canTapOnHeader != null);
Remove the shadow and/or dividers
Go to the bottom of the expansion_panel.dart file. This is where the build method should be. At the bottom of the build method should be the return statement, which returns MergeableMaterial. You can do the following:
return MergeableMaterial(
hasDividers: false, //Change the boolean value of this
children: items,
elevation: 0,
//Add this line to remove shadow from elevation, REQUIRES ANOTHER STEP
);
If add the "elevation: 0" property you MUST go back to mergeable_material.dart and add the following line of code:
void _paintShadows(Canvas canvas, Rect rect) {
if (boxShadows == null) return; //ADD THIS LINE OF CODE
for (BoxShadow boxShadow in boxShadows) {
final Paint paint = boxShadow.toPaint();
// TODO(dragostis): Right now, we are only interpolating the border radii
// of the visible Material slices, not the shadows; they are not getting
// interpolated and always have the same rounded radii. Once shadow
// performance is better, shadows should be redrawn every single time the
// slices' radii get interpolated and use those radii not the defaults.
canvas.drawRRect(kMaterialEdges[MaterialType.card].toRRect(rect), paint);
}
}
I think you get the idea, You can do more to remove padding and whatnot by messing around with constants.
Concerns
Note: I'm relatively new to flutter, (2 months last summer and 2 months now- I'm a college student) in fact. I don't know how modifying these files may impact other widgets but I haven't noticed any issues by doing this.
This is also my first post so take it with a grain of salt. Modifying Material implementations may break some rules or conventions that I would refer to the documentation for.
Instead of changing the source code, you're better off making a copy of the expansion_panel.dart and using this. For the space between the items to disappear, you must comment out on lines 486 and 487.
if (_isChildExpanded(index) && index != 0 && !_isChildExpanded(index - 1))
items.add(MaterialGap(key: _SaltedKey<BuildContext, int>(context, index * 2 - 1)));
And on lines 558 and 559.
if (_isChildExpanded(index) && index != widget.children.length - 1)
items.add(MaterialGap(key: _SaltedKey<BuildContext, int>(context, index * 2 + 1)));
Another issue with this component which you might want to fix, is with the canTapOnHeader property. Setting it to true allows you to tap the card and expand, but you're stuck with a bunch of dead space on the right side of your card. To fix this, add a check to only show expandIconContainer (line 526) as follows:
if (!child.canTapOnHeader) expandIconContainer,
The ExpansionPanelList has an elevation property, which is causing the panels to appear separated. If you don't set the elevation, it is automatically set to a value of 2. To remove the space between expanded panels, you can set the elevation to 0.
However, when you do this, you may run into other graphical issues. For example, the divider doesn't appear for an expanded panel. Without the space between panels, it makes it had to see where one panel starts and the next ends. Not a tough fix to custom code your own dividers in, but thought it was worth mentioning.
When creating a very simple scrollable list in Flutter, what are the advantages and disadvantages of saying (where widgets is List<Widget> == true):
Option 1:
var widget = new SingleChildScrollView(
child: new Column(
chidren: widgets
));
Option 2:
var widget = new ListView(children: widgets);
ListView:
Listview Widget shows the unlimited number of children inside it, but the main advantage of using ListView is it renders only visible items on the screen perhaps more specifically I would say ListView.Builder()
Column
The column is used when we have to draw different widgets in the list. If items increase in the column then SingleChildScrollView is used for scrolling purposes.
For More Reference:
https://medium.com/flutterworld/flutter-problem-listview-vs-column-singlechildscrollview-43fdde0fa355
Definitely go for option 2.
ListView have a few cool optimisations. https://youtu.be/UUfXWzp0-DU?t=33m38s