总而言之:

选项1:使用反射来应用字体(结合weston和Roger Huang的回答):

import java.lang.reflect.Field;
import android.content.Context;
import android.graphics.Typeface;

public final class FontsOverride { 

    public static void setDefaultFont(Context context,
            String staticTypefaceFieldName, String fontAssetName) {
        final Typeface regular = Typeface.createFromAsset(context.getAssets(),
                fontAssetName);
        replaceFont(staticTypefaceFieldName, regular);
    } 

    protected static void replaceFont(String staticTypefaceFieldName,final Typeface newTypeface) {
        if (isVersionGreaterOrEqualToLollipop()) {
            Map<String, Typeface> newMap = new HashMap<String, Typeface>();
            newMap.put("sans-serif", newTypeface);
            try {
                final Field staticField = Typeface.class.getDeclaredField("sSystemFontMap");
                staticField.setAccessible(true);
                staticField.set(null, newMap);
            } catch (NoSuchFieldException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        } else {
            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();
            } 
        }
    }

} 

应用类使用:

public final class Application extends android.app.Application {
    @Override 
    public void onCreate() { 
        super.onCreate(); 
        FontsOverride.setDefaultFont(this, "DEFAULT", "MyFontAsset.ttf");
        FontsOverride.setDefaultFont(this, "MONOSPACE", "MyFontAsset2.ttf");
        FontsOverride.setDefaultFont(this, "SERIF", "MyFontAsset3.ttf");
        FontsOverride.setDefaultFont(this, "SANS_SERIF", "MyFontAsset4.ttf");
    } 
} 

设置一个样式来强制字体应用程序宽(基于lovefish):

Pre-Lollipop:

<resources>
    <style name="AppBaseTheme" parent="Theme.AppCompat.Light">
    </style>

   <!-- Application theme. -->
   <style name="AppTheme" parent="AppBaseTheme">
       <item name="android:typeface">monospace</item>
   </style>
</resources>

棒棒糖(21火):

<resources>
    <style name="AppBaseTheme" parent="Theme.AppCompat.Light">
    </style>

   <!-- Application theme. -->
   <style name="AppTheme" parent="AppBaseTheme">
       <item name="android:textAppearance">@style/CustomTextAppearance</item>
   </style>

   <style name="CustomTextAppearance">
       <item name="android:typeface">monospace</item>
   </style>
</resources>

选项2:子类每个和每个视图，你需要自定义字体，即。ListView, EditTextView, Button等(Palani的答案):

public class CustomFontView extends TextView {

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

public CustomFontView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init(); 
} 

public CustomFontView(Context context) {
    super(context);
    init(); 
} 

private void init() { 
    if (!isInEditMode()) {
        Typeface tf = Typeface.createFromAsset(getContext().getAssets(), "Futura.ttf");
        setTypeface(tf);
    } 
} 

选项3:实现一个视图爬虫，遍历当前屏幕的视图层次结构:

变体#1(汤姆的回答):

public static final void setAppFont(ViewGroup mContainer, Typeface mFont, boolean reflect)
{ 
    if (mContainer == null || mFont == null) return;

    final int mCount = mContainer.getChildCount();

    // Loop through all of the children. 
    for (int i = 0; i < mCount; ++i)
    { 
        final View mChild = mContainer.getChildAt(i);
        if (mChild instanceof TextView)
        { 
            // Set the font if it is a TextView. 
            ((TextView) mChild).setTypeface(mFont);
        } 
        else if (mChild instanceof ViewGroup)
        { 
            // Recursively attempt another ViewGroup. 
            setAppFont((ViewGroup) mChild, mFont);
        } 
        else if (reflect)
        { 
            try { 
                Method mSetTypeface = mChild.getClass().getMethod("setTypeface", Typeface.class);
                mSetTypeface.invoke(mChild, mFont); 
            } catch (Exception e) { /* Do something... */ }
        } 
    } 
} 

用法:

final ViewGroup mContainer = (ViewGroup) findViewById(
android.R.id.content).getRootView();
HomeActivity.setAppFont(mContainer, Typeface.createFromAsset(getAssets(),
"fonts/MyFont.ttf"));

变化# 2:https://coderwall.com/p/qxxmaa/android-use-a-custom-font-everywhere。

选项#4:使用称为书法的第三方自由。

就我个人而言，我会推荐选项4，因为它省去了很多麻烦。

我还想改进weston对API 21 Android 5.0的回答。

我的三星s5在使用默认字体时也遇到了同样的问题。(与其他字体的工作很好)

我设法使它工作通过设置字体(“sans”为例)在XML文件，为每个Textview或按钮

<TextView
android:layout_width="match_parent"
android:layout_height="39dp"
android:textColor="@color/abs__background_holo_light"
android:textSize="12sp"
android:gravity="bottom|center"
android:typeface="sans" />

在MyApplication类中:

public class MyApplication extends Application {
    @Override
    public void onCreate() {
    TypefaceUtil.overrideFont(getApplicationContext(), "SANS_SERIF",
    "fonts/my_font.ttf");
    }
}

希望能有所帮助。

Tom的解决方案很好，但只适用于TextView和EditText。

如果你想覆盖大部分的视图(RadioGroup, TextView，复选框…)，我创建了一个方法:

protected void changeChildrenFont(ViewGroup v, Typeface font){
    for(int i = 0; i < v.getChildCount(); i++){

        // For the ViewGroup, we'll have to use recursivity
        if(v.getChildAt(i) instanceof ViewGroup){
            changeChildrenFont((ViewGroup) v.getChildAt(i), font);
        }
        else{
            try {
                Object[] nullArgs = null;
                //Test wether setTypeface and getTypeface methods exists
                Method methodTypeFace = v.getChildAt(i).getClass().getMethod("setTypeface", new Class[] {Typeface.class, Integer.TYPE});
                //With getTypefaca we'll get back the style (Bold, Italic...) set in XML
                Method methodGetTypeFace = v.getChildAt(i).getClass().getMethod("getTypeface", new Class[] {});
                Typeface typeFace = ((Typeface)methodGetTypeFace.invoke(v.getChildAt(i), nullArgs));
                //Invoke the method and apply the new font with the defined style to the view if the method exists (textview,...)
                methodTypeFace.invoke(v.getChildAt(i), new Object[] {font, typeFace == null ? 0 : typeFace.getStyle()});
            }
            //Will catch the view with no such methods (listview...)
            catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

该方法将返回视图集的XML样式(粗体，斜体…)，并在它们存在时应用它们。

对于ListView，我总是创建一个适配器，并在getView中设置字体。

这很简单… 1.下载并把你的自定义字体在资产..然后写一个单独的类文本视图如下:在这里我使用futura字体

public class CusFntTextView extends TextView {

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

public CusFntTextView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
}

public CusFntTextView(Context context) {
    super(context);
    init();
}

private void init() {
    if (!isInEditMode()) {
        Typeface tf = Typeface.createFromAsset(getContext().getAssets(), "Futura.ttf");
        setTypeface(tf);
    }
}

}

并在XML中执行以下操作:

 <com.packagename.CusFntTextView
        android:id="@+id/tvtitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"         
        android:text="Hi Android"           
        android:textAppearance="?android:attr/textAppearanceLarge"
      />

package com.theeasylearn.demo.designdemo;
import android.content.Context;
import android.graphics.Typeface;
import android.util.AttributeSet;
import android.widget.TextView;

public class MyButton extends TextView {

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

    public MyButton(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public MyButton(Context context) {
        super(context);
        init();
    }

    private void init() {

            Typeface tf =
                    Typeface.createFromAsset(
                            getContext().getAssets(), "angelina.TTF");
            setTypeface(tf);

    }

}

为萨玛林工作。Android:

类:

public class FontsOverride
{
    public static void SetDefaultFont(Context context, string staticTypefaceFieldName, string fontAssetName)
    {
        Typeface regular = Typeface.CreateFromAsset(context.Assets, fontAssetName);
        ReplaceFont(staticTypefaceFieldName, regular);
    }

    protected static void ReplaceFont(string staticTypefaceFieldName, Typeface newTypeface)
    {
        try
        {
            Field staticField = ((Java.Lang.Object)(newTypeface)).Class.GetDeclaredField(staticTypefaceFieldName);
            staticField.Accessible = true;
            staticField.Set(null, newTypeface);
        }
        catch (Exception e)
        {
            Console.WriteLine(e.Message);
        }
    }
}

应用程序实现:

namespace SomeAndroidApplication
{
    [Application]
    public class App : Application
    {
        public App()
        {

        }

        public App(IntPtr handle, JniHandleOwnership transfer)
            : base(handle, transfer)
        {

        }

        public override void OnCreate()
        {
            base.OnCreate();

            FontsOverride.SetDefaultFont(this, "MONOSPACE", "fonts/Roboto-Light.ttf");
        }
    }
}

风格:

<style name="Theme.Storehouse" parent="Theme.Sherlock">
    <item name="android:typeface">monospace</item>
</style>