Develop Reference

How to add custom fonts globally

How to change custom fonts in android studio? It seems like there is no easy way to do such a simple thing. I see that you can change the font of TextView but to change the font for a particular element, drawer or globally I can't seem to find an explenation.

Just Like #tycj said in the comments, unfortunately there is no way to set global fonts to the Textviews. But you can set custom type-styles and apply them as "textAppearance" to the TextViews.
For instance: Assume you have such a style in your project
<style name="MyAPP.TextAppearance.Headline1" parent="TextAppearance.MaterialComponents.Headline1">
<item name="fontFamily">#font/your_font</item>
<item name="android:textSize">48sp</item>
</style>
Then , you simply apply this to your theme.Like this :
<item name="textAppearanceHeadline1">#style/MyAPP.TextAppearance.Headline1</item>
Now you can free to use this in a TextView but as the name of the style suggest, it is better to use this for the hearder TextViews in your app.
<TextView
...
android:textAppearance="?attr/textAppearanceHeadline1" />
the good thing is that you can override these attributes
<TextView
...
android:textAppearance="?attr/textAppearanceHeadline1"
android:textSize="36sp" />
To get further information, you can check here. Also I suggest checking this sample project as well

Why are some of my styles not working with lower APIs?

I have a quick question!
In my styles.xml file, I have
<style name="TextViewStyle" parent="android:Widget.TextView">
<item name="android:padding">20px</item>
<item name="android:background">#9cd0e8</item>
<item name="android:textColor">#254b7c</item>
<item name="android:textSize">18sp</item>
<item name="android:textStyle">bold</item>
</style>
And in my activity_main.xml, I have
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:theme="#+styles/TextViewStyle"
android:text="Sample Text"/>
What I am trying to do is, in my Android application, on a certain activity I plan to place many TextViews with similar properties. Instead of writing these 'properties' every time with each TextView instance, I grouped them together in a style in styles.xml file and set theme of each of my TextViews to that style.
It works fine and does what I want it to do, but only with APIs above 21! My application's supposed to support devices from API level 15 up. Why is my approach not working with lower APIs?
Please help soon. I need to finish this soon.
EDIT
By 'working', I meant that the attributes I set in my style (padding, color, etc.) appear on the TextViews as they should. In lower APIs however, the TextViews appear as if I had not applied any attribute on them. Plain text appears instead of a styled one.

remove parent from your style
remove android:theme from textView, (why there is + sign?)
instead of theme put this into your textView
style="#style/TextViewStyle"
btw, use dp instead of px ;)

How does an android:attr style work?

I'm trying to build an Android UI via layouts. I start with the following:
<TextView
android:id="#+id/..."
android:layout_marginTop="8dip"
android:text="..."
style="?android:attr/listSeparatorTextViewStyle"/>
And that looks good (all caps, smaller font, dividing bar underneath it). Now I want to extend the style, so I change it to the following:
<TextView
android:id="#+id/..."
android:layout_marginTop="8dip"
android:text="..."
style="#style/section_title"/>
With a style of:
<style name="section_title" parent="#android:attr/listSeparatorTextViewStyle">
<item name="android:layout_width">fill_parent</item>
<item name="android:layout_height">wrap_content</item>
</style>
And that doesn't work (font is correct, but the divider line is gone).
How come... that?

When you're using:
style="?android:attr/listSeparatorTextViewStyle"
you're using the style pointed by this attribute(listSeparatorTextViewStyle). If you look in the platform themes.xml you'll see that the style that is actually used for this attribute is Widget.TextView.ListSeparator.White. So this is the style you should extend in your custom style.
Unfortunately that style is private and you can't extend it, or you shouldn't extend it(for reference, see this bug report from google). Your best option would be to copy that entire style, Widget.TextView.ListSeparator.White(Widget.TextView.ListSeparator isn't public as well so would have to also copy that), in your custom style and use that instead of extending the style from the android platform(see this response from the link above).

Android - use attributes to tweak custom styles

here's my issue. I have defined custom themes and styles, so as to customize various Views, in the relevant .xml files. Here are some code extracts:
themes.xml:
...
<style name="Legacy" parent="android:Theme.NoTitleBar">
<item name="android:buttonStyle">#style/Legacy.Button</item>
...
</style>
styles.xml:
...
<style name="Legacy.Button" parent="#android:style/Widget.Button">
<item name="android:textColor">#ffffff</item>
<item name="android:background">#drawable/button_selector_blue</item>
<item name="android:textSize">15dp</item>
</style>
Let's say I set my application's theme to Legacy. If I use a Button in a layout, it will get my custom default parameters (white text, background is #drawable/button_selector_blue, etc).
Now let's say I want to keep those parameters save for the text size: I'd like to have some buttons with a larger text size, which would be defined in an titleSize attribute in attrs.xml:
...
<attr name="titleSize" format="reference|dimension" />
and which value is set for each theme in my themes.xml file.
So my layout would contain something like:
<Button
android:id="#+idmyButtonId"
android:drawableRight="#drawable/aDrawable"
android:text="#string/someText"
android:textSize="?titleSize"
android:layout_width="fill_parent" android:layout_height="wrap_content">
</Button>
When launching my app I get the following error:
java.lang.UnsupportedOperationException: Can't convert to dimension: type=0x2
So it seems I cannot tweak custom styles using attributes - at least not this way. Is such a thing possible ? If not, what would you use to achieve such a result ?
I'd like to give the user the ability to select among different themes, so I can't just define an additionnal ButtonWithLargeText style and directly use it in my layout.
Thanks for your help !

I finally got it to work. Instead of defining my titles' size in attrs.xml, I used dimens.xml. So now the following works:
<Button
android:id="#+idmyButtonId"
android:drawableRight="#drawable/aDrawable"
android:text="#string/someText"
android:textSize="#dimen/titleSize"
android:layout_width="fill_parent" android:layout_height="wrap_content">
</Button>
While I get my regular text size (which I defined in my styles.xml) on the Button by using this:
<Button
android:id="#+id/idRegularButton"
android:text="#string/regularSizeText"
android:layout_width="wrap_content" android:layout_height="wrap_content">
</Button>

TextAppearance in theme

I want to set the text appearance in my theme to be TextAppearnance.Large.
Here is what I am doing in my styles.xml (my application is pointing to this theme in my manifest)
<style name="myTheme" parent="android:Theme.NoTitleBar.Fullscreen">
<item name="android:textAppearance">#android:style/TextAppearance.Large</item>
</style>
Problem:
My text is still being displayed small.
Question(s):
What am I doing wrong in trying to use a predefined TextAppearance in my activity? i.e. How do specify this TextAppearance correctly?
Where are the TextSizes for TextAppearance.Large/Medium/Small defined?

First, declare the attribute as
<item name="android:textAppearance">?android:attr/textAppearanceLarge</item>
But declaring text appearance or text color in a theme only affects text that has absolutely no style or attribute anywhere, including system-defined ones. If you add a
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Medium Text" />
without even the android:textAppearance="?android:attr/textAppearanceMedium" line that Eclipse throws in, it will be affected by this theme, but buttons and the like never will.

themes and styles are defined in the themes.xml and styles.xml files of the sdk implementations in your environment (distinct ones for different android versions or sdk levels).
search your computer for themes.xml (you will probably find multiple instances of it in the "program files/android" folder on a windows 32-bit machine, for example).
this post explains how to customize these attributes.
you can also set explicit size attributes in your xml layout file, by modifying the TextView tag attributes:
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="15sp is the 'normal' size."
android:textSize="15sp"
/>
this post explains how to customize android fonts (including fontType, fontColor, shadow, bold, italic) directly in xml layout file.