This seems like it should be simple but I cannot seem to find an answer.
When I have a Widget (Stateful or Stateless) that I'm using as an image (for example: SvgPicture, CachedNetworkImage, or FadeInImage) and I need to have an ImageProvider, how can I make that conversion?
For a FadeInImage I can use FadeInImage( image: i, placeholder: p).image.
SvgPicture and CachedNetworkImage do not have a .image property.
Is there a generic way to convert a widget to an ImageProvider ?
I tried ImageProvider( widget ) but ImageProvider is abstract - so another way to ask this question could be:
Is there an instance of ImageProvider that simply takes a widget as a parameter ?
For CachedNetworkImage you can use CachedNetworkImageProvider("YOUR URL HERE")
For FadeInImage you can use AssetImage("") as your Image Provide.
I am not sure about SvgPicture but I'm sure you can find it in the documentation given on Pub.dev
Related
I am displaying an Image with filter effects on Screen using in filter
Image.file(
imageFile,
color: color.withOpacity(0.5),
colorBlendMode: BlendMode.hardLight,
),
I need to write these color effects to 'imagefile'
Image.file(); is a widget, if you need to write widget to a disk as an image.
Take a look at this Creating raw image from Widget or Canvas
otherwise, if you need to edit an image(like adding a filter)
maybe it works
How To Create A Filtered Image In Flutter
or below package
https://pub.dev/packages/photofilters
enter image description here
please help me ..how is it possible replace the image with card view and the list with ListView (using silverappbar or anything else)
You can use the Visibility class.
It has a replacement attribute.
Its great that should work.
The code for it can be used like this:
Visibility(
visible: bool_var,
replacement: _showTopCard,
child: image,
)
When bool_var is true, the child widget will be shown and when the bool_var is false the replacement widget will shown.
But make sure that you use widgets as the parameters for replacement and child
The official documentation is:
https://api.flutter.dev/flutter/widgets/Visibility-class.html
And if you want to know more about this class in detail and how to use it in different ways, this link might help:
https://medium.com/#danle.sdev/widget-hide-and-seek-a-guide-to-managing-flutter-widgets-visibility-d7977cbaf444
There are answers related to this topic but they offer workarounds rather than explanations.
Why can't an Image be used where an ImageProvider is required? Conceptually they sound the same to me.
child: new CircleAvatar(
backgroundImage: NetworkImage("https..."), // works
backgroundImage: Image.asset('images/image.png'), // error
),
The error generated by trying to use an image directly is:
error: The argument type 'Image' can't be assigned to the parameter type 'ImageProvider'.
Image vs ImageProvider
An image provider is what provides the image to an Image widget. ;D
The image provider doesn't necessarily have the image right there but it knows how to get it.
Getting an Image
If you need an Image widget, then use one of these:
Image.asset()
Image.network()
Image.file()
Image.memory()
Getting an ImageProvider
If you need an ImageProvider, then use one of these:
AssetImage()
NetworkImage()
FileImage()
MemoryImage()
Converting an ImageProvider to an Image
If you have an ImageProvider object and you want an Image widget, then do the following:
Image(
image: myImageProvider,
)
Converting an Image to an ImageProvider
If you have an Image widget and you need its ImageProvider, then do the following:
myImageWidget.image
An Image is a widget that displays an image.
The ImageProvider instead allows you to identify an image without knowing exactly where is the final asset. The place of the asset will be resolved later when someone wants to read the image.
Actually Every background and Foreground Decoration will accept only ImageProvider like AssetImage(),NetworkImage(),FileImage(),MemoryImage()...
And when you try to build a widget then its take Image.asset(),Image.network(), Image.file(), Image.memory()...
For example, i getting a list of restaurant from database and i only want the url of the image to put into the AssetImage but it cant work. I try to use Image.asset but the Imageprovider cannot put Image.asset.
final restaurantlist = _restaurant.restaurant[index];
AssetImage(restaurantlist.imageurl); <--- error
Image.asset(restuarantlist.imagerurl); <--- working fine
any idea why AssetImage cant work?
Image has several constructors.
Image, for obtaining an image from an ImageProvider.
Image.asset, for obtaining an image from an AssetBundle using a
key.
Image.network, for obtaining an image from a URL.
Image.file, for obtaining an image from a File.
Image.memory, for obtaining an image from a Uint8List.
AssetImage class
fetches an image from an AssetBundle,
and Inherits
ImageProvider < AssetBundleImageKey >
Identifies an image without committing to the precise final asset.
TL;DR
When downloading images use:
Image.network(imgUrl)
In flutter, you can show images with Image Widget it takes a property called image which takes any class which extends ImageProvider class which is used to resolve the image you want Since the AssetImage extends ImageProvider it will just resolve your image assets, you will need to provide it to an Image Widget like so:
Image(image: AssetImage(restaurantlist.imageurl));
And the Image.asset is just a shorthand for the above code.
instead of AssetImage use FileImage
DecorationImage(
image: FileImage("your image url") as ImageProvider,
fit: BoxFit.cover,
),
this is my example to have dynamic background for your app
you cans just use FileImage instead of AssetImage
When I start to think about those two components I find myself arguing about why should I use one instead of the other. Some questions that come to my mind:
What are the differences between a Container and SizedBox?
I understand that Container can have other parameters like padding or decoration, but if I will not use those, why should I use a SizedBox instead of a Container?
There are performance differences between them?
Small Update: When used for whitespace, there is now even a linter warning to prefer SizedBox instead of Container. The main advantage seems to be that SizedBox can be const and won't even create a new instance during runtime.
Thanks to the magic of open source, you don't have to guess too much.
Container is basically just a convenience widget which sometimes saves you to nest 4 other widgets. If you pass width/height into the Container:
constraints =
(width != null || height != null)
? constraints?.tighten(width: width, height: height)
?? BoxConstraints.tightFor(width: width, height: height)
: constraints,
Which will result in:
if (constraints != null)
current = ConstrainedBox(constraints: constraints, child: current);
And the ConstrainedBox in effect is pretty much the same as a SizedBox, just more flexible.
A SizedBox will do:
#override
RenderConstrainedBox createRenderObject(BuildContext context) {
return RenderConstrainedBox(
additionalConstraints: _additionalConstraints,
);
}
BoxConstraints get _additionalConstraints {
return BoxConstraints.tightFor(width: width, height: height);
}
ie. It is effectively the same. If you only use Container for width/height there might be a very minor minor negligible performance overhead. but you most certainly will not be able to measure it.. But I would still recommend SizedBox because it's way clearer. imho.
I'd like to add that SizedBox is not only simpler, but it also can be made const, while Container cannot. This may or may not be something you need.
If you need a box with color you cannot use SizedBox. But https://pub.dev/packages/assorted_layout_widgets has the Box widget, which is something between a SizedBox and a Container: You can have color and it can be made const. Note I am the author of this package.
SizedBox() is a widget for giving some constant height or width between two widgets. It does not contain any decorative properties just like color, borderRadius etc.
On the other hand Container() is a widget that any person can modify according to his/her needs.
Just go through properties of both widgets you will see a huge difference between them.
SizedBox and Container creates a RenderObject. The RenderObject lives in the render tree and some computations are performed on it, even if it paints nothing on the screen.
We can do better, we can have a widget which does not create a RenderObject, while being still valid. The Nil widget is the minimal implementation for this use case. It only creates an Element and does nothing while it's building. Because the optimal way to use it, is to call const Nil(), it also comes with a nil constant that you can use everywhere (which is a const Nil()).