private void setTypefaceFromAttrs(String familyName, int typefaceIndex, int styleIndex) {
    Typeface tf = null;
    if (familyName != null) {
      tf = Typeface.create(familyName, styleIndex);
      if (tf != null) {
        setTypeface(tf);
        return;
      }
    }
    switch (typefaceIndex) {
      case SANS:
        tf = Typeface.SANS_SERIF;
        break;

      case SERIF:
        tf = Typeface.SERIF;
        break;

      case MONOSPACE:
        tf = Typeface.MONOSPACE;
        break;
    }

    setTypeface(tf, styleIndex);
  }

AssetManager mgr = getAssets();
Typeface tf = Typeface.createFromAsset(mgr, "fonts/NotoSansCJKsc-Black.otf");
tv_1.setTypeface(tf);

public class CustomTextView extends TextView
{

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

  //重写设置字体方法
  @Override
  public void setTypeface(Typeface tf)
  {
    tf = Typeface.createFromAsset(getContext().getAssets(), "fonts/NotoSansCJKsc-Light.otf");
    super.setTypeface(tf);
  }
}

  <com.test.fontfamily.CustomTextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:padding="6dp"
    android:text="自定义字体"
    android:textSize="24dp"
    />

package com.test.fontfamily;

import android.app.Application;
import android.content.Context;
import android.graphics.Typeface;
import android.support.annotation.NonNull;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.lang.ref.SoftReference;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by Administrator on 2017/10/24.
 */

public class FontUtils
{

  private static final String TAG = FontUtils.class.getSimpleName();
  private Map<String, SoftReference<Typeface>> mCache = new HashMap<>();
  private static FontUtils sSingleton = null;

  public static Typeface DEFAULT = Typeface.DEFAULT;

  // disable instantiate
  private FontUtils()
  {
  }

  public static FontUtils getInstance()
  {
    // double check
    if (sSingleton == null)
    {
      synchronized (FontUtils.class)
      {
        if (sSingleton == null)
        {
          sSingleton = new FontUtils();
        }
      }
    }
    return sSingleton;
  }

  /**
   * <p>Replace the font of specified view and it's children</p>
   *
   * @param root   The root view.
   * @param fontPath font file path relative to 'assets' directory.
   */
  public void replaceFontFromAsset(@NonNull View root, @NonNull String fontPath)
  {
    replaceFont(root, createTypefaceFromAsset(root.getContext(), fontPath));
  }

  /**
   * <p>Replace the font of specified view and it's children</p>
   *
   * @param root   The root view.
   * @param fontPath font file path relative to 'assets' directory.
   * @param style  One of {@link Typeface#NORMAL}, {@link Typeface#BOLD}, {@link Typeface#ITALIC}, {@link Typeface#BOLD_ITALIC}
   */
  public void replaceFontFromAsset(@NonNull View root, @NonNull String fontPath, int style)
  {
    replaceFont(root, createTypefaceFromAsset(root.getContext(), fontPath), style);
  }

  /**
   * <p>Replace the font of specified view and it's children</p>
   *
   * @param root   The root view.
   * @param fontPath The full path to the font data.
   */
  public void replaceFontFromFile(@NonNull View root, @NonNull String fontPath)
  {
    replaceFont(root, createTypefaceFromFile(fontPath));
  }

  /**
   * <p>Replace the font of specified view and it's children</p>
   *
   * @param root   The root view.
   * @param fontPath The full path to the font data.
   * @param style  One of {@link Typeface#NORMAL}, {@link Typeface#BOLD}, {@link Typeface#ITALIC}, {@link Typeface#BOLD_ITALIC}
   */
  public void replaceFontFromFile(@NonNull View root, @NonNull String fontPath, int style)
  {
    replaceFont(root, createTypefaceFromFile(fontPath), style);
  }

  /**
   * <p>Replace the font of specified view and it's children with specified typeface</p>
   */
  private void replaceFont(@NonNull View root, @NonNull Typeface typeface)
  {
    if (root == null || typeface == null)
    {
      return;
    }

    if (root instanceof TextView)
    { // If view is TextView or it's subclass, replace it's font
      TextView textView = (TextView) root;
      // Extract previous style of TextView
      int style = Typeface.NORMAL;
      if (textView.getTypeface() != null)
      {
        style = textView.getTypeface().getStyle();
      }
      textView.setTypeface(typeface, style);
    } else if (root instanceof ViewGroup)
    { // If view is ViewGroup, apply this method on it's child views
      ViewGroup viewGroup = (ViewGroup) root;
      for (int i = 0; i < viewGroup.getChildCount(); ++i)
      {
        replaceFont(viewGroup.getChildAt(i), typeface);
      }
    } // else return
  }

  /**
   * <p>Replace the font of specified view and it's children with specified typeface and text style</p>
   *
   * @param style One of {@link Typeface#NORMAL}, {@link Typeface#BOLD}, {@link Typeface#ITALIC}, {@link Typeface#BOLD_ITALIC}
   */
  private void replaceFont(@NonNull View root, @NonNull Typeface typeface, int style)
  {
    if (root == null || typeface == null)
    {
      return;
    }
    if (style < 0 || style > 3)
    {
      style = Typeface.NORMAL;
    }

    if (root instanceof TextView)
    { // If view is TextView or it's subclass, replace it's font
      TextView textView = (TextView) root;
      textView.setTypeface(typeface, style);
    } else if (root instanceof ViewGroup)
    { // If view is ViewGroup, apply this method on it's child views
      ViewGroup viewGroup = (ViewGroup) root;
      for (int i = 0; i < viewGroup.getChildCount(); ++i)
      {
        replaceFont(viewGroup.getChildAt(i), typeface, style);
      }
    } // else return
  }

  /**
   * <p>Create a Typeface instance with specified font file</p>
   *
   * @param fontPath font file path relative to 'assets' directory.
   * @return Return created typeface instance.
   */
  private Typeface createTypefaceFromAsset(Context context, String fontPath)
  {
    SoftReference<Typeface> typefaceRef = mCache.get(fontPath);
    Typeface typeface = null;
    if (typefaceRef == null || (typeface = typefaceRef.get()) == null)
    {
      typeface = Typeface.createFromAsset(context.getAssets(), fontPath);
      typefaceRef = new SoftReference<>(typeface);
      mCache.put(fontPath, typefaceRef);
    }
    return typeface;
  }

  private Typeface createTypefaceFromFile(String fontPath)
  {
    SoftReference<Typeface> typefaceRef = mCache.get(fontPath);
    Typeface typeface = null;
    if (typefaceRef == null || (typeface = typefaceRef.get()) == null)
    {
      typeface = Typeface.createFromFile(fontPath);
      typefaceRef = new SoftReference<>(typeface);
      mCache.put(fontPath, typefaceRef);
    }
    return typeface;
  }

  /**
   * <p>Replace system default font. <b>Note:</b>you should also add code below to your app theme in styles.xml. </p>
   * {@code <item name="android:typeface">monospace</item>}
   * <p>The best place to call this method is {@link Application#onCreate()}, it will affect
   * whole app font.If you call this method after view is visible, you need to invalid the view to make it effective.</p>
   *
   * @param context {@link Context Context}
   * @param fontPath font file path relative to 'assets' directory.
   */
  public void replaceSystemDefaultFontFromAsset(@NonNull Context context, @NonNull String fontPath)
  {
    replaceSystemDefaultFont(createTypefaceFromAsset(context, fontPath));
  }

  /**
   * <p>Replace system default font. <b>Note:</b>you should also add code below to your app theme in styles.xml. </p>
   * {@code <item name="android:typeface">monospace</item>}
   * <p>The best place to call this method is {@link Application#onCreate()}, it will affect
   * whole app font.If you call this method after view is visible, you need to invalid the view to make it effective.</p>
   *
   * @param context {@link Context Context}
   * @param fontPath The full path to the font data.
   */
  public void replaceSystemDefaultFontFromFile(@NonNull Context context, @NonNull String fontPath)
  {
    replaceSystemDefaultFont(createTypefaceFromFile(fontPath));
  }

  /**
   * <p>Replace system default font. <b>Note:</b>you should also add code below to your app theme in styles.xml. </p>
   * {@code <item name="android:typeface">monospace</item>}
   * <p>The best place to call this method is {@link Application#onCreate()}, it will affect
   * whole app font.If you call this method after view is visible, you need to invalid the view to make it effective.</p>
   */
  private void replaceSystemDefaultFont(@NonNull Typeface typeface)
  {
    modifyObjectField(null, "MONOSPACE", typeface);
  }

  private void modifyObjectField(Object obj, String fieldName, Object value)
  {
    try
    {
      Field defaultField = Typeface.class.getDeclaredField(fieldName);
      defaultField.setAccessible(true);
      defaultField.set(obj, value);

    } catch (NoSuchFieldException e)
    {
      e.printStackTrace();
    } catch (IllegalAccessException e)
    {
      e.printStackTrace();
    }
  }
}

FontUtils.getInstance().replaceFontFromAsset(View root, String fontPath)

FontUtils.getInstance().replaceSystemDefaultFontFromAsset(this,"fonts/NotoSansCJKsc-Thin.otf");

<item name="android:typeface">monospace</item>