How can I detect if a Row will overflow, to hide the overflowing elements and replace them with a single button "+X" to indicate how many elements have been hidden?
You can check the size of the screen by using
MediaQuery.of(context).size.width
then do the math (divide the widget by the size width then get rounded down. Using below the Truncating Division operator)
<Widget Width> ~/ MediaQuery.of(context).size.width
to find out how many components fit in and check how many will be left out of screen.
For example:
If my Widget width is 20 and my screen (or Parent Widget) width is 110, the above operation will result in 5
which means 5 elements will be rendered and the others should be factored in your "+ button"
If you want to know your Parent Widget Width and it is variable, check this answer here: https://stackoverflow.com/a/41558369/5666202
Related
What are the differences between SliverList and SliverFixedExtentList in Flutter?
According to the documentation of each widget:
SliverList: "A sliver that places multiple box children in a linear array along the main axis."
SliverFixedExtentList: "A sliver that places multiple box children with the same main axis extent in a linear array."
It seems that we should use SliverFixedExtentList over SliverList if all children have the same main axis extent. However, what does "same main axis extent" really mean?
It means all children have the same height. If you are familiar with ListView, it has itemExtent property that does the same thing.
Essentially, if you cannot guarantee all list items will have "equal size on the main axis" (e.g. equal height on a vertical scrolling list, or equal width on a horizontal scrolling list), then we cannot know the "exact size" of each item in the list, until we load it. However, if you can guarantee that they will all have the same size, for example, 100 units in height, then we don't need to load each item to measure its size.
Knowing item size before loading them is very useful when you want to jump a large distance. For example, if you want to scroll 10,000 px down, and if we know each item is fixed at 200 px tall, then we can easily jump 50 items, just load the 51th item and display it. If we don't know that (if you cannot guarantee that) then we will have to literally lay out all items in-between to see where 10,000 px will land us.
While I debug my flutter app, at certain points I see warnings like this:
Bottom overflow by 1234 pixel
BoxConstraints have a negative value
I suppose, my concept of Flutter viewport / layout isn't correct:
Currently, I image an infinite drawing area, where I declaratively
define widgets.
Widgets, which are too large, get drawn outside the
viewport [or clipped].
Could you please refine my probably wrong concept?
This happens when the size [height, width] exceeds the the total size of the screen.
For example : the aspect ratio height of mobile screen is 500 and the size.height of button is 600, then the Bottom overflow by 100 pixel.
Generally overflow means, that the widget you want to paint on the screen crosses the border of the screen and therefore isn't visible anymore... This can also happen if you implement non scrollable columns in containers of a certain height... Usually, you can wrap your widget in a SingleChildScrollView widget and as a child choose a column/row (depending on the direction you want it to be aligned...) or make a list view and set the scrolldirection property to Axis.vertical or Axis.horizontal...
My Flutter UI has a Row widget with and arbitrary number Widgets in it. I would like to move all of those widgets over to the right by a fixed amount. But the caveat is, if the other widgets grow in width such that the available horizontal space is consumed, the spacing widget will relinquish its space.
The Spacer widget does not work for me, as it does not allow you to specify a fix maximum. It only allows a flex value, which is a function of the width of the other content in the row. I want this spacer to take up a fixed amount of space regardless of the width of the other content of the row (unless all the room is used up).
Try using sizedBox or FractionallySizedBox as explained in this answer
https://stackoverflow.com/a/63430801/8213343
I'm trying to produce a widget like this below to be contained inside of a listview. I have managed an effect like this rather simply based on the example given on the flutter website for YouTube. However, the part I'm struggling with is that I would like the image to resize vertically depending on how large the text is.
Currently this is created with a row. If possible I'd like to set the row height somehow but only dependent on the height of the text. As some elements will have more text and some will have less I would like to have the image fill the vertical space so the height is the same as the text height.
I basically want this - https://api.flutter.dev/flutter/material/ListTile-class.html#material.ListTile.4
but where the image height on the left matches the text height on the right
Thanks in advance!
I am coming to Flutter from a web background, where I am used to defining screen elements in terms of percentages of the height and width of the screen, or of elements that contain them.
I just completed a course.
Now that I am enthused and want to start building an app, I am a little confused, as the course only spoke of heights & widths in absolute pixel values. I can see this being problematic with different aspect rations, and especially with different orientations.
Is there a canonical approach to this? The official docs also seem to use absolute pixel values, so maybe I am missing a fundamental point.
A search suggests that I might use MediaQuery and then scale everything according to that. But, I don't see widespread use of that in code samples.
Is there a non-opinionated standard approach?
I am a little confused, as the course only spoke of heights & widths in absolute pixel values.
Actually, flutter uses density independent pixels (dp) for width/height arguments. dp actually scale with resolution, meaning 1 dp is displayed as the same PHYSICAL distance on every device. You don't have to worry about your elements being displayed at different sizes, just because the resolution of the screen they're on changes.
To be precise, flutter calls them logical pixel and:
By definition, there are roughly 38 logical pixels per centimeter, or about 96 logical pixels per inch, of the physical display.
So think about them as you would think about cm.
I am used to defining screen elements in terms of percentages of the height and width of the screen
Nonetheless, you might want to layout your widgets in a relative fashion (relative to the screen or the parent). For that purpose, flutter has different solutions:
Flexible
Expanded
Wrap
MediaQuery
LayoutBuilder
GridView
other layout options
Is there a non-opinionated standard approach?
It is a very opinionated question to begin with, but for example, Material design is a common standard for mobile-design. Flutters layout widgets are based around this approach.
But in the end, it is your design choice. For example, to achieve a responsive layout grid you could use Wrap, or you could use LayoutBuilder and determine yourself how you would like to layout rows and columns.
I would recommend you to scale widgets based on the size of the screen. This allows your application to be more flexible and adjust to various platforms and sizes such as large tablets or small phones. In order to do this, I recommend you to use the widget FractionallySizedBox which allows you to size widgets using a percentage of the screen size. For example, if you want a button widget to fill up 50 percent of a screen's width you can use the following code:
Container(
alignment: Alignment.center,
child: FractionallySizedBox(
widthFactor: 0.5,
child: FlatButton(
onTap: () {},
child: Text("PRESS HERE")
)
)
)
This code creates a button positioned in the center of the screen with a width of 50 percent of the screen size's width. You can also change the height of the button with the heightFactor field. By using this code the button widget will scale up and scale down for different screen sizes while still maintaining a size of half of the screen's width. For more resources, you should check out this video by the Flutter Team: https://youtu.be/PEsY654EGZ0 and their website on the FractionallySizedBox here: https://api.flutter.dev/flutter/widgets/FractionallySizedBox-class.html.
The FractionallySizedBox however is only one of many different approaches to making your flutter app fit to different screen sizes. Another approach is to use the AspectRatio Widget. Below is an example of this:
Container(
alignment: Alignment.center,
child: AspectRatio(
aspectRatio: 3/2
child: FlatButton(
onTap: () {},
child: Text("PRESS ME")
)
)
)
This code will create a button with a 3 to 2 ratio between its width and height. If the screen size changes the button will increase or decrease in size accordingly while again maintaining the 3 to 2 ratio. If you want more information the Flutter team also has a video on it (https://youtu.be/XcnP3_mO_Ms) along with some documentation here:(https://api.flutter.dev/flutter/widgets/AspectRatio-class.html).
Both widgets are perfectly fine and are considered standard practice to use but I personally use FractionallySizedBox more.
I hope my answer was helpful.