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Android: Creating a custom component programmatically does not reflect the style applied

Created a custom button which extends AppCompatButton. The following are the constructors used:
public CustomButton(Context context)
{
this(context, null);
}
public CustomButton(Context context, AttributeSet attrs)
{
this(context, attrs, R.style.customStyle);
}
public CustomButton(final Context context, final AttributeSet attrs, final int defStyleAttr)
{
super(context, attrs, defStyleAttr);
}
Constructing CustomButton through XML works fine. However, when constructed in Java, it does not reflect the customStyle properties. Tried debugging the code. Though it passes through the second constructor doesn't take up the properties.
Any leads would be highly appreciated.

I was able to solve this by creating a ContextThemeWrapper object when creating CustomButton programmatically.
In activity file:
CustomButton customButton = new CustomButton( new ContextThemeWrapper(this, R.style.customStyle));

Custom font not getting applied

My Custom Font class
public class CustomFontText extends TextView {
/*
* Caches typefaces based on their file path and name, so that they don't have to be created every time when they are referenced.
*/
private static Typeface mTypeface;
public CustomFontText(final Context context) {
super(context, null);
}
public CustomFontText(final Context context, final AttributeSet attrs) {
super(context, attrs, 0);
readAttrs(context, attrs);
}
public CustomFontText(final Context context, final AttributeSet attrs, final int defStyle) {
super(context, attrs, defStyle);
readAttrs(context, attrs);
}
private void readAttrs(Context context, AttributeSet attrs) {
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.CustomTextView);
// Read the title and set it if any
String fontName = a.getString(R.styleable.CustomTextView_fontname);
if (fontName != null) {
// We have a attribute value
if (mTypeface == null) {
mTypeface = Typeface.createFromAsset(context.getAssets(), fontName);
setTypeface(mTypeface);
}
}
// a.recycle();
}
}
Applying in XMl file
<somepackage.CustomFontText
android:id="#+id/details"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="ewfewfewqfewfwef"
custom:fontname="Roboto-Regular.ttf" />
It is not giving any kind of error but I am not able to view any changes in the textview. Changing the fontname makes no difference.

Moving the code setTypeface(mTypeface); outside the check for mTypeface == null should solve the issue. So the code should look like this:
if (mTypeface == null) {
mTypeface = Typeface.createFromAsset(context.getAssets(), fontName);
}
setTypeface(mTypeface);
This is because mTypeface is declared static and such all CustomFontText instances share the same typeface (which makes sense for caching). If setTypeface is called inside the check though, it will only get applied once, when the typeface is first loaded.

Actually I don't know why yours not working, however, alternatively you can use Calligraphy by chrisjenx. I used it in one of my projects and it works great!

Create folder fonts in the assets folder of your project and instead of using just the font name for custom:fontname, use the path to the file.
custom:fontname="fonts/Roboto-Regular.ttf"

Add ttf or otf file in your assets folder.
Create custom class extends with TextView
public class CustomText extends TextView {
public CustomText (Context context) {
super(context);
createTextView(context, null);
}
public CustomEditText(Context context, AttributeSet attrs) {
super(context, attrs);
createTextView(context, attrs);
}
public CustomEditText(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
createTextView(context, null);
}
private void createTextView(Context context, AttributeSet attrs) {
String fontName;
TypedArray typedArray;
if (isInEditMode())
return;
if (attrs != null) {
typedArray = context.obtainStyledAttributes(attrs, R.styleable.FontTypeFace, 0, 0);
fontName = typedArray.getString(R.styleable.FontTypeFace_typeface);
setFontTypeFace(context, fontName);
typedArray.recycle();
}
}
private void setFontTypeFace(Context context, String fontName) {
if (fontName != null) {
Typeface typeface = Typeface.createFromAsset(context.getAssets(), fontName);
setTypeface(typeface);
}
}
}
declare stylable in your attrs file :
<declare-styleable name="FontTypeFace">
<attr name="typeface" format="string" />
</declare-styleable>
Create control using custom textview in xml file :
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#color/white"
android:orientation="horizontal"
android:weightSum="1">
<com.Widget.CustomTextView
android:id="#+id/txt_time"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="#dimen/dimen_text_size_12"
app:typeface="#string/thin" />
</LinearLayout>
Just add the assets file name inside string.xml file
<!--String for assets font type file name -->
<string name="bold">bold.otf</string>
<string name="light">light.otf</string>
<string name="medium">medium.otf</string>
<string name="regular">regular.otf</string>
<string name="regular_italic">regular_italic.otf</string>
<string name="semi_bold">semibold.otf</string>
<string name="thin">thin.otf</string>

How to read android default attributes of a View in java code

I want to have a custom TextView called MyTextView and i want to set a default TextSize in it's constructor only if no TextSize has been set in it's XML definition. How can i detect if a TextSize has been set in it's XML definition?
public class MyTextView extends TextView{
public MyTextView(Context context, AttributeSet attrs) {
super(context, attrs);
//How can i read TextSize from AttribureSet??
//if no TextSize has been set then SetTextSize(defaultTextSize);
}
}
Can any one help me please?

You can obtain style attributes like
public class MyTextView extends TextView{
public MyTextView(Context context, AttributeSet attrs) {
super(context, attrs);
String size = attrs.getAttributeValue("http://schemas.android.com/apk/res/android", "textSize");
}
}

Here's example:
final Resources.Theme theme = context.getTheme();
TypedArray array = theme.obtainStyledAttributes(attrs, R.styleable.YourStylable, R.attr.YourDefStyleAttr, 0);

Try this float size = new TextView(this).getTextSize();

Using custom font in android TextView using xml

I have added a custom font file to my assets/fonts folder. How do I use it from my XML?
I can use it from code as follows:
TextView text = (TextView) findViewById(R.id.textview03);
Typeface tf = Typeface.createFromAsset(getAssets(), "fonts/Molot.otf");
text.setTypeface(tf);
Can't I do it from XML using an android:typeface="/fonts/Molot.otf" attribute?

Short answer: No. Android doesn't have built-in support for applying custom fonts to text widgets through XML.
However, there's a workaround that's not terribly difficult to implement.
First
You'll need to define your own stylable. In your /res/values folder, open/create the attrs.xml file and add a declare-styleable object like so:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="FontText">
<attr name="typefaceAsset" format="string"/>
</declare-styleable>
</resources>
Second
Assuming you want to use this widget often, you should set up a simple cache for the loaded Typeface objects, since loading them from memory on the fly can take time. Something like:
public class FontManager {
private static FontManager instance;
private AssetManager mgr;
private Map<String, Typeface> fonts;
private FontManager(AssetManager _mgr) {
mgr = _mgr;
fonts = new HashMap<String, Typeface>();
}
public static void init(AssetManager mgr) {
instance = new FontManager(mgr);
}
public static FontManager getInstance() {
if (instance == null) {
// App.getContext() is just one way to get a Context here
// getContext() is just a method in an Application subclass
// that returns the application context
AssetManager assetManager = App.getContext().getAssets();
init(assetManager);
}
return instance;
}
public Typeface getFont(String asset) {
if (fonts.containsKey(asset))
return fonts.get(asset);
Typeface font = null;
try {
font = Typeface.createFromAsset(mgr, asset);
fonts.put(asset, font);
} catch (Exception e) {
}
if (font == null) {
try {
String fixedAsset = fixAssetFilename(asset);
font = Typeface.createFromAsset(mgr, fixedAsset);
fonts.put(asset, font);
fonts.put(fixedAsset, font);
} catch (Exception e) {
}
}
return font;
}
private String fixAssetFilename(String asset) {
// Empty font filename?
// Just return it. We can't help.
if (TextUtils.isEmpty(asset))
return asset;
// Make sure that the font ends in '.ttf' or '.ttc'
if ((!asset.endsWith(".ttf")) && (!asset.endsWith(".ttc")))
asset = String.format("%s.ttf", asset);
return asset;
}
}
This one will allow you to use .ttc file extensions, but it's untested.
Third
Create a new class that subclasses TextView. This particular example takes into account the defined XML typeface (bold, italic, etc.) and apply it to the font (assuming you're using a .ttc file).
/**
* TextView subclass which allows the user to define a truetype font file to use as the view's typeface.
*/
public class FontText extends TextView {
public FontText(Context context) {
this(context, null);
}
public FontText(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public FontText(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
if (isInEditMode())
return;
TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.FontText);
if (ta != null) {
String fontAsset = ta.getString(R.styleable.FontText_typefaceAsset);
if (!TextUtils.isEmpty(fontAsset)) {
Typeface tf = FontManager.getInstance().getFont(fontAsset);
int style = Typeface.NORMAL;
float size = getTextSize();
if (getTypeface() != null)
style = getTypeface().getStyle();
if (tf != null)
setTypeface(tf, style);
else
Log.d("FontText", String.format("Could not create a font from asset: %s", fontAsset));
}
}
}
}
Finally
Replace the instances of TextView in your XML with the fully qualified class name. Declare your custom namespace just like you would the Android namespace. Note that the "typefaceAsset" should point to a .ttf or .ttc file contained in your /assets directory.
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:custom="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.example.FontText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="This is a custom font text"
custom:typefaceAsset="fonts/AvenirNext-Regular.ttf"/>
</RelativeLayout>

Here is example code that does this. I have the font defined in a static final variable and the font file is in the assets directory.
public class TextViewWithFont extends TextView {
public TextViewWithFont(Context context, AttributeSet attrs) {
super(context, attrs);
this.setTypeface(MainActivity.typeface);
}
public TextViewWithFont(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
this.setTypeface(MainActivity.typeface);
}
public TextViewWithFont(Context context) {
super(context);
this.setTypeface(MainActivity.typeface);
}
}

Create your customed TextView belong to the font you want to use. In this class, I use a static mTypeface field to cache the Typeface (for better performance)
public class HeliVnTextView extends TextView {
/*
* Caches typefaces based on their file path and name, so that they don't have to be created every time when they are referenced.
*/
private static Typeface mTypeface;
public HeliVnTextView(final Context context) {
this(context, null);
}
public HeliVnTextView(final Context context, final AttributeSet attrs) {
this(context, attrs, 0);
}
public HeliVnTextView(final Context context, final AttributeSet attrs, final int defStyle) {
super(context, attrs, defStyle);
if (mTypeface == null) {
mTypeface = Typeface.createFromAsset(context.getAssets(), "HelveticaiDesignVnLt.ttf");
}
setTypeface(mTypeface);
}
}
In xml file:
<java.example.HeliVnTextView
android:id="#+id/textView1"
android:layout_width="0dp"
... />
In java class:
HeliVnTextView title = new HeliVnTextView(getActivity());
title.setText(issue.getName());

Activity implements LayoutInflater.Factory2 that provides callbacks on each created View.
It's possible to style the TextView with custom font Family attribute, load the typefaces on demand and call setTypeface on instantiated text views automatically.
Unfortunately due to the architectural relationship of Inflater instances relative to Activities and Windows the simplest approach to use custom fonts in android is to cache loaded fonts on the Application level.
The sample code base is here:
https://github.com/leok7v/android-textview-custom-fonts
<style name="Baroque" parent="#android:style/TextAppearance.Medium">
<item name="android:layout_width">fill_parent</item>
<item name="android:layout_height">wrap_content</item>
<item name="android:textColor">#F2BAD0</item>
<item name="android:textSize">14pt</item>
<item name="fontFamily">baroque_script</item>
</style>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:custom="http://schemas.android.com/apk/res/custom.fonts"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
style="#style/Baroque"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="#string/sample_text"
/>
results in

Not a good idea to use custom fonts in xml due to this fact
that is, you have to do it programmatically to avoid the memory leak!

UPDATE: https://github.com/chrisjenx/Calligraphy appears to be a
superior solution to this.
Maybe you can use reflection to inject/hack your font into the static list of available fonts when your application is created? I am interested in feedback from others if this is a really, really bad idea or if this is a great solution — it seems it is going to be one of those extremes...
I was able to inject my custom typeface into the list of system typefaces with my own font family name, then specifying that custom font family name ("brush-script") as the value of android:FontFamily on a standard TextView worked on my LG G4 running Android 6.0.
public class MyApplication extends android.app.Application
{
#Override
public void onCreate()
{
super.onCreate();
Typeface font = Typeface.createFromAsset(this.getResources().getAssets(),"fonts/brush-script.ttf");
injectTypeface("brush-script", font);
}
private boolean injectTypeface(String fontFamily, Typeface typeface)
{
try
{
Field field = Typeface.class.getDeclaredField("sSystemFontMap");
field.setAccessible(true);
Object fieldValue = field.get(null);
Map<String, Typeface> map = (Map<String, Typeface>) fieldValue;
map.put(fontFamily, typeface);
return true;
}
catch (Exception e)
{
Log.e("Font-Injection", "Failed to inject typeface.", e);
}
return false;
}
}
In my layout
<TextView
android:id="#+id/name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Fancy Text"
android:fontFamily="brush-script"/>

Create a fonts folder in assets and add all your required font's there.
public class CustomTextView extends TextView {
private static final String TAG = "TextView";
public CustomTextView(Context context) {
super(context);
}
public CustomTextView(Context context, AttributeSet attrs) {
super(context, attrs);
setCustomFont(context, attrs);
}
public CustomTextView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setCustomFont(context, attrs);
}
private void setCustomFont(Context ctx, AttributeSet attrs) {
TypedArray a = ctx.obtainStyledAttributes(attrs, R.styleable.CustomTextView);
String customFont = a.getString(R.styleable.CustomTextView_customFont);
setCustomFont(ctx, customFont);
a.recycle();
}
public boolean setCustomFont(Context ctx, String fontName) {
Typeface typeface = null;
try {
if(fontName == null){
fontName = Constants.DEFAULT_FONT_NAME;
}
typeface = Typeface.createFromAsset(ctx.getAssets(), "fonts/" + fontName);
} catch (Exception e) {
Log.e(TAG, "Unable to load typeface: "+e.getMessage());
return false;
}
setTypeface(typeface);
return true;
}
}
and add a declarable in attrs.xml
<declare-styleable name="CustomTextView">
<attr name="customFont" format="string"/>
</declare-styleable>
and then add your customFont like
app:customFont="arial.ttf"

I know this is an old question, but i've found a much easier solution.
First declare your TextView in xml as usual.
Put your font (TTF or TTC) in the asset folder
app\src\main\assets\
Then just set the typeface for your text view in your onCreate method.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_name);
TextView textView = findViewById(R.id.my_textView);
Typeface typeface = Typeface.createFromAsset(getAssets(), "fontName.ttf");
textView.setTypeface(typeface);
}
Done.

The best solution is to use (finally) introduced by Google a native custom font feature in XML. But you have to target API 26. It supports API 16+
https://developer.android.com/guide/topics/ui/look-and-feel/fonts-in-xml

instead of xmlns:custom="schemas.android.com/tools"; you should use: xmlns:custom="schemas.android.com/apk/res-auto"; in order to use styleable attributes.
I made this change and it is working now.

the latest update now that you can set the font in XML without any other classes added like:
android:fontFamily="#font_folder/font_file"

Custom fonts and XML layouts (Android)

I'm trying to define a GUI layout using XML files in Android. As far as I can find out, there is no way to specify that your widgets should use a custom font (e.g. one you've placed in assets/font/) in XML files and you can only use the system installed fonts.
I know that, in the Java code, I could change the font of each widget manually using unique IDs. Alternatively, I could iterate over all the widgets in Java to make this change, but this would probably be very slow.
What other options do I have? Is there any better ways to making widgets that have a custom look? I don't particularly want to have to manually change the font for every new widget I add.

You can extend TextView to set custom fonts as I learned here.
TextViewPlus.java:
package com.example;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Typeface;
import android.util.AttributeSet;
import android.util.Log;
import android.widget.TextView;
public class TextViewPlus extends TextView {
private static final String TAG = "TextView";
public TextViewPlus(Context context) {
super(context);
}
public TextViewPlus(Context context, AttributeSet attrs) {
super(context, attrs);
setCustomFont(context, attrs);
}
public TextViewPlus(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setCustomFont(context, attrs);
}
private void setCustomFont(Context ctx, AttributeSet attrs) {
TypedArray a = ctx.obtainStyledAttributes(attrs, R.styleable.TextViewPlus);
String customFont = a.getString(R.styleable.TextViewPlus_customFont);
setCustomFont(ctx, customFont);
a.recycle();
}
public boolean setCustomFont(Context ctx, String asset) {
Typeface tf = null;
try {
tf = Typeface.createFromAsset(ctx.getAssets(), asset);
} catch (Exception e) {
Log.e(TAG, "Could not get typeface: "+e.getMessage());
return false;
}
setTypeface(tf);
return true;
}
}
attrs.xml: (in res/values)
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="TextViewPlus">
<attr name="customFont" format="string"/>
</declare-styleable>
</resources>
main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:foo="http://schemas.android.com/apk/res/com.example"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<com.example.TextViewPlus
android:id="#+id/textViewPlus1"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:text="#string/showingOffTheNewTypeface"
foo:customFont="saxmono.ttf">
</com.example.TextViewPlus>
</LinearLayout>
You would put "saxmono.ttf" in the assets folder.
UPDATE 8/1/13
There are serious memory concerns with this method. See chedabob's comment below.

I'm 3 years late for the party :( However this could be useful for someone who might stumble upon this post.
I've written a library that caches Typefaces and also allow you to specify custom typefaces right from XML. You can find the library here.
Here is how your XML layout would look like, when you use it.
<com.mobsandgeeks.ui.TypefaceTextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world"
geekui:customTypeface="fonts/custom_font.ttf" />

This might be a little late, but you need to create a singleton class that returns the custom typeface to avoid memory leaks.
TypeFace class:
public class OpenSans {
private static OpenSans instance;
private static Typeface typeface;
public static OpenSans getInstance(Context context) {
synchronized (OpenSans.class) {
if (instance == null) {
instance = new OpenSans();
typeface = Typeface.createFromAsset(context.getResources().getAssets(), "open_sans.ttf");
}
return instance;
}
}
public Typeface getTypeFace() {
return typeface;
}
}
Custom TextView:
public class NativelyCustomTextView extends TextView {
public NativelyCustomTextView(Context context) {
super(context);
setTypeface(OpenSans.getInstance(context).getTypeFace());
}
public NativelyCustomTextView(Context context, AttributeSet attrs) {
super(context, attrs);
setTypeface(OpenSans.getInstance(context).getTypeFace());
}
public NativelyCustomTextView(Context context, AttributeSet attrs,
int defStyle) {
super(context, attrs, defStyle);
setTypeface(OpenSans.getInstance(context).getTypeFace());
}
}
By xml:
<com.yourpackage.views.NativelyCustomTextView
android:id="#+id/natively_text_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_margin="20dp"
android:text="#string/natively"
android:textSize="30sp" />
Programmatically:
TextView programmaticallyTextView = (TextView)
findViewById(R.id.programmatically_text_view);
programmaticallyTextView.setTypeface(OpenSans.getInstance(this)
.getTypeFace());

Old question, but I sure wish I read this answer here before I started my own search for a good solution. Calligraphy extends the android:fontFamily attribute to add support for custom fonts in your asset folder, like so:
<TextView
android:text="#string/hello_world"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="fonts/Roboto-Bold.ttf"/>
The only thing you have to do to activate it is attaching it to the Context of the Activity you're using:
#Override
protected void attachBaseContext(Context newBase) {
super.attachBaseContext(new CalligraphyContextWrapper(newBase));
}
You can also specify your own custom attribute to replace android:fontFamily
It also works in themes, including the AppTheme.

Using DataBinding :
#BindingAdapter({"bind:font"})
public static void setFont(TextView textView, String fontName){
textView.setTypeface(Typeface.createFromAsset(textView.getContext().getAssets(), "fonts/" + fontName));
}
In XML:
<TextView
app:font="#{`Source-Sans-Pro-Regular.ttf`}"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
font file must be in assets/fonts/

If you only have one typeface you would like to add, and want less code to write, you can create a dedicated TextView for your specific font. See code below.
package com.yourpackage;
import android.content.Context;
import android.graphics.Typeface;
import android.util.AttributeSet;
import android.widget.TextView;
public class FontTextView extends TextView {
public static Typeface FONT_NAME;
public FontTextView(Context context) {
super(context);
if(FONT_NAME == null) FONT_NAME = Typeface.createFromAsset(context.getAssets(), "fonts/FontName.otf");
this.setTypeface(FONT_NAME);
}
public FontTextView(Context context, AttributeSet attrs) {
super(context, attrs);
if(FONT_NAME == null) FONT_NAME = Typeface.createFromAsset(context.getAssets(), "fonts/FontName.otf");
this.setTypeface(FONT_NAME);
}
public FontTextView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
if(FONT_NAME == null) FONT_NAME = Typeface.createFromAsset(context.getAssets(), "fonts/FontName.otf");
this.setTypeface(FONT_NAME);
}
}
In main.xml, you can now add your textView like this:
<com.yourpackage.FontTextView
android:id="#+id/tvTimer"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="" />

The best way to do it From Android O preview release is this way
1.)Right-click the res folder and go to New > Android resource directory. The New
Resource Directory window appears.
2.)In the Resource type list, select font, and then click OK.
3.)Add your font files in the font folder.The folder structure below generates R.font.dancing_script, R.font.la_la, and R.font.ba_ba.
4.)Double-click a font file to preview the file's fonts in the editor.
Next we must create a font family
1.)Right-click the font folder and go to New > Font resource file. The New Resource File window appears.
2.)Enter the file name, and then click OK. The new font resource XML opens in the editor.
3.)Enclose each font file, style, and weight attribute in the font tag element. The following XML illustrates adding font-related attributes in the font resource XML:
<?xml version="1.0" encoding="utf-8"?>
<font-family xmlns:android="http://schemas.android.com/apk/res/android">
<font
android:fontStyle="normal"
android:fontWeight="400"
android:font="#font/hey_regular" />
<font
android:fontStyle="italic"
android:fontWeight="400"
android:font="#font/hey_bababa" />
</font-family>
Adding fonts to a TextView:
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
**android:fontFamily="#font/ba_ba"**/>
As from the documentation
Working With Fonts
all the steps are correct.

Extend TextView and give it a custom attribute or just use the android:tag attribute to pass in a String of what font you want to use. You will need to pick a convention and stick to it such as I will put all of my fonts in the res/assets/fonts/ folder so your TextView class knows where to find them. Then in your constructor you just set the font manually after the super call.

The only way to use custom fonts is through the source code.
Just remember that Android runs on devices with very limited resources and fonts might require a good amount of RAM. The built-in Droid fonts are specially made and, if you note, have many characters and decorations missing.

I might have a simple answer for the question without extending the TextView and implementing a long code.
Code :
TextView tv = (TextView) findViewById(R.id.textview1);
tv.setTypeface(Typeface.createFromAsset(getAssets(), "font.ttf"));
Place the custom font file in assets folder as usual and try this. It works for me.
I just dont understand why peter has given such a huge code for this simple thing or he has given his answer in old version.

Also can be defined in the xml without creating custom classes
style.xml
<style name="ionicons" parent="android:TextAppearance">
<!-- Custom Attr-->
<item name="fontPath">fonts/ionicons.ttf</item>
</style>
activity_main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="#style/ionicons"
android:text=""/>
</LinearLayout>
A quick note, because I just always forgot where to put the fonts, its that the font must be inside assets and this folder resides in the same level that res and src, in my case its assets/fonts/ionicons.ttf
Updated Added root layout because this method needs xmlns:app="http://schemas.android.com/apk/res-auto" to work
Update 2 Forgot about a library that I've installed before called Calligraphy

Peter's answer is the best, but it can be improved by using the styles.xml from Android to customize your fonts for all textviews in your app.
My code is here

There are two ways to customize fonts :
!!! my custom font in assets/fonts/iran_sans.ttf
Way 1 :
Refrection Typeface.class ||| best way
call FontsOverride.setDefaultFont() in class extends Application, This code will cause all software fonts to be changed, even Toasts fonts
AppController.java
public class AppController extends Application {
#Override
public void onCreate() {
super.onCreate();
//Initial Font
FontsOverride.setDefaultFont(getApplicationContext(), "MONOSPACE", "fonts/iran_sans.ttf");
}
}
FontsOverride.java
public class FontsOverride {
public static void setDefaultFont(Context context, String staticTypefaceFieldName, String fontAssetName) {
final Typeface regular = Typeface.createFromAsset(context.getAssets(), fontAssetName);
replaceFont(staticTypefaceFieldName, regular);
}
private static void replaceFont(String staticTypefaceFieldName, final Typeface newTypeface) {
try {
final Field staticField = Typeface.class.getDeclaredField(staticTypefaceFieldName);
staticField.setAccessible(true);
staticField.set(null, newTypeface);
} catch (NoSuchFieldException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
Way 2: use setTypeface
for special view just call setTypeface() to change font.
CTextView.java
public class CTextView extends TextView {
public CTextView(Context context) {
super(context);
init(context,null);
}
public CTextView(Context context, #Nullable AttributeSet attrs) {
super(context, attrs);
init(context,attrs);
}
public CTextView(Context context, #Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init(context,attrs);
}
#RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
public CTextView(Context context, #Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
init(context,attrs);
}
public void init(Context context, #Nullable AttributeSet attrs) {
if (isInEditMode())
return;
// use setTypeface for change font this view
setTypeface(FontUtils.getTypeface("fonts/iran_sans.ttf"));
}
}
FontUtils.java
public class FontUtils {
private static Hashtable<String, Typeface> fontCache = new Hashtable<>();
public static Typeface getTypeface(String fontName) {
Typeface tf = fontCache.get(fontName);
if (tf == null) {
try {
tf = Typeface.createFromAsset(AppController.getInstance().getApplicationContext().getAssets(), fontName);
} catch (Exception e) {
e.printStackTrace();
return null;
}
fontCache.put(fontName, tf);
}
return tf;
}
}

Here's a tutorial that shows you how to setup a custom font like #peter described: http://responsiveandroid.com/2012/03/15/custom-fonts-in-android-widgets.html
it also has consideration for potential memory leaks ala http://code.google.com/p/android/issues/detail?id=9904 . Also in the tutorial is an example for setting a custom font on a button.

You can make easily custom textview class :-
So what you need to do first, make Custom textview class which extended with AppCompatTextView.
public class CustomTextView extends AppCompatTextView {
private int mFont = FontUtils.FONTS_NORMAL;
boolean fontApplied;
public CustomTextView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(attrs, context);
}
public CustomTextView(Context context, AttributeSet attrs) {
super(context, attrs);
init(attrs, context);
}
public CustomTextView(Context context) {
super(context);
init(null, context);
}
protected void init(AttributeSet attrs, Context cxt) {
if (!fontApplied) {
if (attrs != null) {
mFont = attrs.getAttributeIntValue(
"http://schemas.android.com/apk/res-auto", "Lato-Regular.ttf",
-1);
}
Typeface typeface = getTypeface();
int typefaceStyle = Typeface.NORMAL;
if (typeface != null) {
typefaceStyle = typeface.getStyle();
}
if (mFont > FontUtils.FONTS) {
typefaceStyle = mFont;
}
FontUtils.applyFont(this, typefaceStyle);
fontApplied = true;
}
}
}
Now , every time Custom text view call and we will get int value from attribute int fontValue = attrs.getAttributeIntValue("http://schemas.android.com/apk/res-auto","Lato-Regular.ttf",-1).
Or
We can also get getTypeface() from view which we set in our xml (android:textStyle="bold|normal|italic"). So do what ever you want to do.
Now, we make FontUtils for set any .ttf font into our view.
public class FontUtils {
public static final int FONTS = 1;
public static final int FONTS_NORMAL = 2;
public static final int FONTS_BOLD = 3;
public static final int FONTS_BOLD1 = 4;
private static Map<String, Typeface> TYPEFACE = new HashMap<String, Typeface>();
static Typeface getFonts(Context context, String name) {
Typeface typeface = TYPEFACE.get(name);
if (typeface == null) {
typeface = Typeface.createFromAsset(context.getAssets(), name);
TYPEFACE.put(name, typeface);
}
return typeface;
}
public static void applyFont(TextView tv, int typefaceStyle) {
Context cxt = tv.getContext();
Typeface typeface;
if(typefaceStyle == Typeface.BOLD_ITALIC) {
typeface = FontUtils.getFonts(cxt, "FaktPro-Normal.ttf");
}else if (typefaceStyle == Typeface.BOLD || typefaceStyle == SD_FONTS_BOLD|| typefaceStyle == FONTS_BOLD1) {
typeface = FontUtils.getFonts(cxt, "FaktPro-SemiBold.ttf");
} else if (typefaceStyle == Typeface.ITALIC) {
typeface = FontUtils.getFonts(cxt, "FaktPro-Thin.ttf");
} else {
typeface = FontUtils.getFonts(cxt, "FaktPro-Normal.ttf");
}
if (typeface != null) {
tv.setTypeface(typeface);
}
}
}

It may be useful to know that starting from Android 8.0 (API level 26) you can use a custom font in XML.
You can apply a custom font to the entire application in the following way.
Put the font in the folder res/font.
In res/values/styles.xml use it in the application theme.
<style name="AppTheme" parent="{whatever you like}">
<item name="android:fontFamily">#font/myfont</item>
</style>

Fontinator is an Android-Library make it easy, to use custom Fonts.
https://github.com/svendvd/Fontinator

You can't extend TextView to create a widget or use one in a widgets layout:
http://developer.android.com/guide/topics/appwidgets/index.html