我知道已经有了很好的答案，但这里有一个完全工作的实现。

这是自定义文本视图:

package com.mycompany.myapp.widget;

/**
 * Text view with a custom font.
 * <p/>
 * In the XML, use something like {@code customAttrs:customFont="roboto-thin"}. The list of fonts
 * that are currently supported are defined in the enum {@link CustomFont}. Remember to also add
 * {@code xmlns:customAttrs="http://schemas.android.com/apk/res-auto"} in the header.
 */
public class CustomFontTextView extends TextView {

    private static final String sScheme =
            "http://schemas.android.com/apk/res-auto";
    private static final String sAttribute = "customFont";

    static enum CustomFont {
        ROBOTO_THIN("fonts/Roboto-Thin.ttf"),
        ROBOTO_LIGHT("fonts/Roboto-Light.ttf");

        private final String fileName;

        CustomFont(String fileName) {
            this.fileName = fileName;
        }

        static CustomFont fromString(String fontName) {
            return CustomFont.valueOf(fontName.toUpperCase(Locale.US));
        }

        public Typeface asTypeface(Context context) {
            return Typeface.createFromAsset(context.getAssets(), fileName);
        }
    }

    public CustomFontTextView(Context context, AttributeSet attrs) {
        super(context, attrs);

        if (isInEditMode()) {
            return;
        } else {
            final String fontName = attrs.getAttributeValue(sScheme, sAttribute);

            if (fontName == null) {
                throw new IllegalArgumentException("You must provide \"" + sAttribute + "\" for your text view");
            } else {
                final Typeface customTypeface = CustomFont.fromString(fontName).asTypeface(context);
                setTypeface(customTypeface);
            }
        }
    }
}

这里是自定义属性。这应该进入你的res/attrs.xml文件:

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

下面是你如何使用它。我将使用一个相对布局来包装它并显示customAttr声明，但它显然可以是您已经拥有的任何布局。

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:customAttrs="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.mycompany.myapp.widget.CustomFontTextView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="foobar"
         customAttrs:customFont="roboto_thin" />

</RelativeLayout>

我以前成功地使用过这个方法。我们的实现之间的唯一区别是，我没有在资产中使用子文件夹。但不确定这是否会改变什么。

由于我对SO的所有解决方案都不满意，所以我提出了我的解决方案。这是基于标签的一个小技巧(即你不能在你的代码中使用标签)，我把字体路径放在那里。所以当定义视图时，你可以这样做:

<TextView
        android:id="@+id/textViewHello1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World 1"
        android:tag="fonts/Oswald-Regular.ttf"/>

或:

<TextView
        android:id="@+id/textViewHello2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World 2"
        style="@style/OswaldTextAppearance"/>

<style name="OswaldTextAppearance">
        <item name="android:tag">fonts/Oswald-Regular.ttf</item>
        <item name="android:textColor">#000000</item>
</style>

现在你可以显式地访问/设置视图如下:

TextView textView = TextViewHelper.setupTextView(this, R.id.textViewHello1).setText("blah");

或者只是通过:

TextViewHelper.setupTextViews(this, (ViewGroup) findViewById(R.id.parentLayout)); // parentLayout is the root view group (relative layout in my case)

你问的魔法课是什么?主要是从另一个SO帖子中粘来的，为活动和片段提供了helper方法:

import android.app.Activity;
import android.content.Context;
import android.graphics.Typeface;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.HashMap;
import java.util.Map;

public class TextViewHelper {
    private static final Map<String, Typeface> mFontCache = new HashMap<>();

    private static Typeface getTypeface(Context context, String fontPath) {
        Typeface typeface;
        if (mFontCache.containsKey(fontPath)) {
            typeface = mFontCache.get(fontPath);
        } else {
            typeface = Typeface.createFromAsset(context.getAssets(), fontPath);
            mFontCache.put(fontPath, typeface);
        }
        return typeface;
    }

    public static void setupTextViews(Context context, ViewGroup parent) {
        for (int i = parent.getChildCount() - 1; i >= 0; i--) {
            final View child = parent.getChildAt(i);
            if (child instanceof ViewGroup) {
                setupTextViews(context, (ViewGroup) child);
            } else {
                if (child != null) {
                    TextViewHelper.setupTextView(context, child);
                }
            }
        }
    }

    public static void setupTextView(Context context, View view) {
        if (view instanceof TextView) {
            if (view.getTag() != null) // also inherited from TextView's style
            {
                TextView textView = (TextView) view;
                String fontPath = (String) textView.getTag();
                Typeface typeface = getTypeface(context, fontPath);
                if (typeface != null) {
                    textView.setTypeface(typeface);
                }
            }
        }
    }

    public static TextView setupTextView(View rootView, int id) {
        TextView textView = (TextView) rootView.findViewById(id);
        setupTextView(rootView.getContext().getApplicationContext(), textView);
        return textView;
    }

    public static TextView setupTextView(Activity activity, int id) {
        TextView textView = (TextView) activity.findViewById(id);
        setupTextView(activity.getApplicationContext(), textView);
        return textView;
    }
}

您可以使用简单的EasyFonts第三方库来设置各种自定义字体到您的TextView。通过使用这个库，你应该不必担心下载和添加字体到assets/fonts文件夹。还有关于字体对象的创建。

而不是

Typeface myTypeface = Typeface.createFromAsset(getAssets(), "fonts/myFont.ttf");
TextView myTextView = (TextView)findViewById(R.id.myTextView);
myTextView.setTypeface(myTypeface);

简单:

TextView myTextView = (TextView)findViewById(R.id.myTextView);
myTextView.setTypeface(EasyFonts.robotoThin(this));

这个库还提供了以下字体面。

Roboto Droid衬线 机器人机器人 自由 有趣的栽培者 Android的国家 绿色的鳄梨 识别

答:更新 Android 8.0 (API级别26)引入了一个新特性，XML字体。 只要在运行Android 4.1 (API级别16)或更高的设备上使用XML字体功能，使用支持库26。

请看这个链接

旧的答案

有两种方法来定制字体:

! !自定义字体 资产/字体/ iran_sans.ttf

方法一: 反射字体。class |||最好的方式

在类extends Application中调用FontsOverride.setDefaultFont()，这段代码将导致所有软件字体被更改，甚至是Toasts字体

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();
        }
    }
}

方法2:使用setTypeface

对于特殊的视图，只需调用setTypeface()来更改字体。

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;
    }

}

如果你想从网络加载字体或轻松地设置它的样式，你可以使用:

https://github.com/shellum/fontView

例子:

<!--Layout-->
<com.finalhack.fontview.FontView
        android:id="@+id/someFontIcon"
        android:layout_width="80dp"
        android:layout_height="80dp" />

//Java:
fontView.setupFont("http://blah.com/myfont.ttf", true, character, FontView.ImageType.CIRCLE);
fontView.addForegroundColor(Color.RED);
fontView.addBackgroundColor(Color.WHITE);