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。

Typeface tf = Typeface.createFromAsset(getAssets(),
        "fonts/DroidSansFallback.ttf");
TextView tv = (TextView) findViewById(R.id.CustomFontText);
tv.setTypeface(tf);

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>

首先下载所需字体的.ttf文件(arial.ttf)。把它放在资产文件夹中。(在assets文件夹内创建名为fonts的新文件夹，并将其放置在其中。)使用以下代码应用字体到你的TextView:

Typeface type = Typeface.createFromAsset(getAssets(),"fonts/arial.ttf"); 
textView.setTypeface(type);

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。

以上答案是正确的。只要确保你在“assets”文件夹下创建了一个名为“fonts”的子文件夹，如果你正在使用这段代码。