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Should we use different dimen files for different screen sizes

Currently, I'm developing Android app (phone only) and using only one size for different screen sizes, ie:
dimens.xml:
<dimen name="button_size">48dp</dimen>
<dimen name="text_size">16sp</dimen>
so in different screen sizes, we have only one size for components. And we go to this result: in small device, a textview can contain 10 chars but in larger device, a textview can contain 20 chars
And some developers use a gradle script to generate multiple dimens files in different folders based on the main dimens file like this:
values-sw320dp
dimens.xml:
<dimen name="button_size">48dp</dimen>
<dimen name="text_size">16sp</dimen>
values-sw480dp
dimens.xml:
<dimen name="button_size">52dp</dimen>
<dimen name="text_size">20sp</dimen>
...
so the system will use the dimens based on device size. And we go to this result: in small device and larger device, a textview can contain the same char, ie: 12 chars.
My question is: which one is better for UI, UX? (using Google Material Design)

You can use this library to support multiple screen dimen here

You can try this below, this will set automatically based on device.
?android:attr/textAppearanceMedium - For Medium font
?android:attr/textAppearanceSmall - For Small font
?android:attr/textAppearanceLarge - For Large font
Please check Material guidelines, To ensure usability for people with disabilities, give buttons a height of 36dp and give touchable targets a minimum height of 48dp.

Best practice is to use different dimens file for different devices. This will help you application view to be same across devices. If you keep same dimens for different devices then layout problem can also come. In some devices your layout will look perfectly fine but in another it will look very bad.
Android developer site also recommend to use different layout for supporting different devices.

Is there any dimens.xml with standart dimensions?

I want to know if is there some web or something with examples of dimens.xml files to support multiple screen sizes?

Android runs on a variety of devices that offer different screen sizes and densities. For applications, the Android system provides a consistent development environment across devices and handles most of the work to adjust each application's user interface to the screen on which it is displayed. At the same time, the system provides APIs that allow you to control your application's UI for specific screen sizes and densities, in order to optimize your UI design for different screen configurations. For example, you might want a UI for tablets that's different from the UI for handsets.
Although the system performs scaling and resizing to make your application work on different screens, you should make the effort to optimize your application for different screen sizes and densities. In doing so, you maximize the user experience for all devices and your users believe that your application was actually designed for their devices—rather than simply stretched to fit the screen on their devices.
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Yes You can make folders of values for in which different dimens values are stored for multiple screen resolutions:
for example you can make folder in res named, values-720x1280, values-320x480, values-240x320 and put dimens.xml in each folder with different values in it...
you can define custom height with dimens(Suppose for 720X1280 device) like this:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="icon_width">55dip</dimen>
<dimen name="icon_height">55dip</dimen>
<dimen name="photo_width">170dip</dimen>
<dimen name="photo_height">155dip</dimen>
</resources>
and for values-320x480 dimens.xml:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="icon_width">20dip</dimen>
<dimen name="icon_height">20dip</dimen>
<dimen name="photo_width">100dip</dimen>
<dimen name="photo_height">100dip</dimen>
</resources>
Then reference them in your other xml:
android:layout_height="#dimen/icon_height">
try it now and tell your experience
From HoneyComb, there is a new way to fix all of this. Your resources folder should now look like this:

Android font size on different screens

I want to use different font size for different screen sizes.
I read about this many articles, but I'm not sure about usage. Is correct to use different dimens resource file for different screen dimensions like code below:
res/values/dimens.xml
res/values-small/dimens.xml
res/values-normal/dimens.xml
res/values-xlarge/dimens.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="text_size">18sp</dimen>
</resources>
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="text_size">24sp</dimen>
</resources>
...
I also read that correct way is to use sp for font size, but this doesn't fit font in different screen dimensions as I expect.
If there, what are the disadvantages of using different dimens for every size?
Thanks

The best way is to create different layout resources for each of the screens you wish to support. Place each of the layouts in a separate folder that designates the width of the screen. For example, normal sized layouts go in your res/layout folder, and a layout resource for a 7 inch tablet (600 pixel width) would go in the res/layout-sw600dp folder. Make the resource names identical, but adjust your font sizes accordingly.

#up Not, it isn't good way.
#topic You can gets width & height of screen (and w&h of View). Next, you can set font, for example 2% of width screen. If you have content 1260x720, 0.02*1260=24,6 px (you can use also (int)24.6 to convert double to int)

I do something very similar and it's worked fine for me. Some people put the values in the various layouts such as Fietser suggested, but if all of your layouts end up being the exact same except for the font size, your approach is better. That way you can have a single layout and only modify the font sizes. But sometimes you might have changes in the actual layout xml, so then it's probably a wash between the two approaches.

Android: How to set XML dimen variables programatically

In my layout XML files, I reference a lot of parameters through a separate files called dimens.xml.
For example, dimens.xml contains parameters like these:
<dimen name="textSize_normal">20dp</dimen>
<dimen name="buttonTextSize_normal">15dp</dimen>
<dimen name="editTextSize_normal">17dp</dimen>
<dimen name="buttonHeight_normal">37dp</dimen>
<dimen name="margin_normal">5dp</dimen>
And in my main.xml, for example, I would set the text size for a TextView by doing something like this:
android:textSize="#dimen/editTextSize_normal"
It works great.
Now, my questions is, is it possible to set the values for the dimen variables in my dimen.xml file programmatically from my main activity? What I am trying to do is fetch the screen size, and set, for example, the textSize based on a fraction of the height of the screen so that it is easily adaptable to any screen size. I have all that figured out, I just need your help to figure out how to set the dimen variables in my code.

Now, my questions is, is it possible to set the values for the dimen variables in my dimen.xml file programmatically from my main activity?
No.
What I am trying to do is fetch the screen size, and set, for example, the textSize based on a fraction of the height of the screen so that it is easily adaptable to any screen size.
Ignoring that this is an odd UI approach, the way to do that is to delete your android:textSize attributes and to change the text size at runtime using setTextSize() in Java.
I have all that figured out, I just need your help to figure out how to set the dimen variables in my code.
You don't "set the dimen variables". You apply your calculations to the widgets, via setters like setTextSize().

No, you can't edit the Resources files on runtime, they are already compiled and generated.

You should use density independent pixels in all your resources, so that dimensions can adapt to screen size. You don't need to calculate that values at runtime. If you want to have a different layout for different screen sizes, then consider using multiple resource files.
Read this guide.

i guess what you mean is to change the size depending on the device's screen size..
which can be made by creating multiple dimens.xml files in folders like values-hdpi, values-xhdpi, values-xxhdpi, values-mdpi,.. and then on runtime the compiler will choose the dimen depending on the dpi
i actually didn't try this before but i read it
here.. take a look at this:
http://developer.android.com/guide/practices/screens_support.html#qualifiers

When should the dimens.xml file be used in Android?

For instance, in a specific layout I have the following XML:
<GridView
android:id="#+id/gridView1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="3dp"
android:columnWidth="48dp"
android:numColumns="auto_fit"
android:verticalSpacing="10dp"
android:horizontalSpacing="10dp"
android:stretchMode="spacingWidth" />
This grid view is specific to this layout and I don't think I'll be using any other grid views with similar properties. That to say that the dimension values in the code are specific to that grid view.
Should I still move them to a dimens.xml file or it's fine to just leave them like that? If so, should I place values in the dimens.xml file only when that value is used across multiple layouts?

I drop dimension values into a dimens.xml resource typically for three reasons:
Reuse: I need multiple widgets or layouts to use the same value and I only want to change it once when updating or tweaking across the application.
Density Difference: If I need the dimension to be slightly smaller or larger from ldpi -> hdpi or small -> large.
Reading in from code: When I'm instantiating a view in the code and want to apply some static dimensions, putting them in dimens.xml as dp (or dip) allowing me to get a scaled value in Java code with Resources.getDimensionPixelSize().

Supplemental answer
#Devunwired lists 3 reasons to use dimens.xml. Here are the details of how to do that.
1. Reuse
If you set some dp or sp value in dimens.xml once like this
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="textview_padding">16dp</dimen>
<dimen name="large_text_size">30sp</dimen>
</resources>
you can reuse it throughout your app in multiple locations.
<TextView
android:padding="#dimen/textview_padding"
android:textSize="#dimen/large_text_size"
... />
<TextView
android:padding="#dimen/textview_padding"
android:textSize="#dimen/large_text_size"
... />
Then when you need to make a change, you only need to do it in one place.
Notes
This is basically the same effect as using a style or theme.
Be careful not to give two different views the same dimen value if they really shouldn't be. If you need to make changes to one set of views but not another, then you will have to go back to each one individually, which defeats the purpose.
2. Size Difference
#Devunwired called this Density difference, but if you are using dp (density independent pixels), this already takes care are the density difference problem for all but the most minor cases. So in my opinion, screen size is a more important factor for using dimens.xml.
An 8dp padding might look great on a phone, but when the app is run on a tablet, it looks too narrow. You can solve this problem by making two (or more) different versions of dimens.xml.
Right click your res folder and choose New > Value resource file. Then write in dimens and choose Smallest Screen Width. Write in 600 for the width (7” tablet). (There are other ways of choosing the sizes. See the documentation and this answer for more.)
This will make another values folder that will be used for devices whose smallest screen width is 600dp. In the Android view the two dimens.xml files look like this.
Now you can modify them independently.
values/dimens.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="my_default_padding">16dp</dimen>
</resources>
values-sw600dp/dimens.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="my_default_padding">64dp</dimen>
</resources>
When using your dimen you only have to set it with the name you used in both dimens.xml files.
<LinearLayout
...
android:padding="#dimen/my_default_padding">
</LinearLayout>
The system will automatically choose the right value for you depending on the device the user is using.
3. Reading in from code
Sometimes it is a pain scaling programmatically between px and dp (see this answer for how).
If you have a fixed dp value already defined in dimens.xml like this
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="my_dp_value">16dp</dimen>
</resources>
Then you can easily get it with
int sizeInPixels = getResources().getDimensionPixelSize(R.dimen.my_dp_value);
and it will already be converted to pixels for whatever density device the user has.

The dimens.xml file is used to keep all the hard-coded pixel values in one place.
Now, although you may not repeatedly use these values right now, it's still a good idea to to place them in dimens.xml for future reference. Besides, following a standard Android programming paradigm helps other developers to understand your code faster. This is much like the strings.xml where we place Strings some of which end up being used only once! :)

I don’t know if it can help you but I wrote a little java programe that allows you to duplicate a dimension xml file with a new desired value so that you no longer have to do it by hand line by line.
https://github.com/Drex-xdev/Dimensions-Scalable-Android