我终于找到了一个非常简单的解决方法。

use these Support libraries in app level gradle, compile 'com.android.support:appcompat-v7:26.0.2' compile 'com.android.support:support-v4:26.0.2' then create a directory named "font" inside the res folder put fonts(ttf) files in that font directory, keep in mind the naming conventions [e.g.name should not contain any special character, any uppercase character and any space or tab] After that, reference that font from xml like this <Button android:id="@+id/btn_choose_employee" android:layout_width="140dp" android:layout_height="40dp" android:layout_centerInParent="true" android:background="@drawable/rounded_red_btn" android:onClick="btnEmployeeClickedAction" android:text="@string/searching_jobs" android:textAllCaps="false" android:textColor="@color/white" android:fontFamily="@font/times_new_roman_test" />

在本例中，times_new_roman_test是该字体目录中的字体ttf文件

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。

添加类FontTextView.java:

public class FontTextView extends TextView {
    String fonts[] = {"HelveticaNeue.ttf", "HelveticaNeueLight.ttf", "motschcc.ttf", "symbol.ttf"};

    public FontTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(attrs);
    }

    public FontTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        if (!isInEditMode()) {
            init(attrs);
        }

    }

    public FontTextView(Context context) {
        super(context);
        if (!isInEditMode()) {
            init(null);
        }
    }

    private void init(AttributeSet attrs) {
        if (attrs != null) {
            TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.FontTextView);
            if (a.getString(R.styleable.FontTextView_font_type) != null) {
                String fontName = fonts[Integer.valueOf(a.getString(R.styleable.FontTextView_font_type))];

                if (fontName != null) {
                    Typeface myTypeface = Typeface.createFromAsset(getContext().getAssets(), "font/" + fontName);
                    setTypeface(myTypeface);
                }
                a.recycle();
            }
        }
    }
}

添加到资产库字体

添加到attrs.xml， 数字应该在数组类中的顺序。 < declare-styleable name = " FontTextView " > <attr name="font_type" format="enum"> <enum name="HelveticaNeue" value="0"/> <enum name="HelveticaNeueLight" value="1"/> <enum name="motschcc" value="2"/> <enum name="symbol" value="3"/> < / attr >

从列表中选择字体

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);

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>

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) {
 }
 }