从资产中获取字体并设置为所有子元素

public static void overrideFonts(final Context context, final View v) {
    try {
        if (v instanceof ViewGroup) {
            ViewGroup vg = (ViewGroup) v;
            for (int i = 0; i < vg.getChildCount(); i++) {
                View child = vg.getChildAt(i);
                overrideFonts(context, child);
         }
        } else if (v instanceof TextView ) {
            ((TextView) v).setTypeface(Typeface.createFromAsset(context.getAssets(),"DroidNaskh.ttf"));// "BKOODB.TTF"));
        }
    } catch (Exception e) {
 }
 } 

最好的实践

TextViewPlus.java:

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 typeface = null;
        try {
            typeface = Typeface.createFromAsset(ctx.getAssets(), asset);
        } catch (Exception e) {
            Log.e(TAG, "Unable to load typeface: "+e.getMessage());
            return false;
        }

        setTypeface(typeface);
        return true;
    }
}

attrs.xml:(在哪里放置res/values)

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="TextViewPlus">
        <attr name="customFont" format="string"/>
    </declare-styleable>
</resources>

使用方法:

<?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-auto"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <com.mypackage.TextViewPlus
        android:id="@+id/textViewPlus1"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:text="@string/showingOffTheNewTypeface"
        foo:customFont="my_font_name_regular.otf">
    </com.mypackage.TextViewPlus>
</LinearLayout>

希望这对你有所帮助。

import java.lang.ref.WeakReference;
import java.util.HashMap;

import android.content.Context;
import android.graphics.Typeface;

public class FontsManager {

    private static FontsManager instance;

    private static HashMap<String, WeakReference<Typeface>> typefaces = new HashMap<String, WeakReference<Typeface>>();

    private static Context context;

    private FontsManager(final Context ctx) {
        if (context == null) {
            context = ctx;
        }
    }

    public static FontsManager getInstance(final Context appContext) {
        if (instance == null) {
            instance = new FontsManager(appContext);
        }
        return instance;
    }

    public static FontsManager getInstance() {
        if (instance == null) {
            throw new RuntimeException(
                    "Call getInstance(Context context) at least once to init the singleton properly");
        }
        return instance;
    }

    public Typeface getFont(final String assetName) {
        final WeakReference<Typeface> tfReference = typefaces.get(assetName);
        if (tfReference == null || tfReference.get() == null) {
            final Typeface tf = Typeface.createFromAsset(context.getResources().getAssets(),
                    assetName);
            typefaces.put(assetName, new WeakReference<Typeface>(tf));
            return tf;
        }
        return tfReference.get();
    }

}

通过这种方式，您可以创建一个继承自TextView的视图，并在其构造函数上调用setTypeface。

Android使用Roboto字体，这是一种非常漂亮的字体，有几种不同的粗细(普通、轻、薄、浓缩)，在高密度屏幕上看起来很棒。

检查下面的链接检查roboto字体:

如何使用Roboto在xml布局

回到你的问题，如果你想改变所有的TextView/按钮在你的应用程序的字体，尝试添加以下代码到你的styles.xml使用Roboto-light字体:

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
    ......
    <item name="android:buttonStyle">@style/MyButton</item>
    <item name="android:textViewStyle">@style/MyTextView</item>
</style>

<style name="MyButton" parent="@style/Widget.AppCompat.Button">
    <item name="android:textAllCaps">false</item>
    <item name="android:fontFamily">sans-serif-light</item>
</style>

<style name="MyTextView" parent="@style/TextAppearance.AppCompat">
    <item name="android:fontFamily">sans-serif-light</item>
</style>

不要忘记在你的AndroidManifest.xml中使用“AppTheme”

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    ......
</application>

首先，默认不是Arial。默认为Droid Sans。

其次，要更改为不同的内置字体，请在布局XML中使用android:typeface或在Java中使用setTypeface()。

第三，Android中没有Helvetica字体。内置选项有Droid Sans (Sans)、Droid Sans Mono (monospace)和Droid Serif (Serif)。虽然您可以将自己的字体与应用程序捆绑在一起，并通过setTypeface()使用它们，但请记住，字体文件很大，在某些情况下需要许可协议(例如Helvetica，一种Linotype字体)。

EDIT

The Android design language relies on traditional typographic tools such as scale, space, rhythm, and alignment with an underlying grid. Successful deployment of these tools is essential to help users quickly understand a screen of information. To support such use of typography, Ice Cream Sandwich introduced a new type family named Roboto, created specifically for the requirements of UI and high-resolution screens. The current TextView framework offers Roboto in thin, light, regular and bold weights, along with an italic style for each weight. The framework also offers the Roboto Condensed variant in regular and bold weights, along with an italic style for each weight.

ICS之后，android包含了Roboto字体样式， 阅读更多Roboto

编辑2

随着支持库26的出现，Android现在支持自定义字体 违约。您可以在res/fonts中插入新的字体，这些字体可以单独以XML或编程方式设置为TextViews。整个应用程序的默认字体也可以通过定义它styles.xml来改变，android开发者文档对此有明确的指导

当你的字体存储在res/asset/fonts/Helvetica.ttf中时，使用以下方法:

Typeface tf = Typeface.createFromAsset(getAssets(),"fonts/Helvetica.ttf"); 
txt.setTypeface(tf);

或者，如果你的字体文件存储在res/font/helvetica.ttf中，使用以下方法:

Typeface tf = ResourcesCompat.getFont(this,R.font.helvetica);
txt.setTypeface(tf);