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);

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

首先，默认不是Arial。默认为Droid Sans。

其次，要更改为不同的内置字体，请在布局XML中使用android:typeface或在Java中使用setTypeface()。

第三，Android中没有Helvetica字体。内置选项有Droid Sans (Sans)、Droid Sans Mono (monospace)和Droid Serif (Serif)。虽然您可以将自己的字体与应用程序捆绑在一起，并通过setTypeface()使用它们，但请记住，字体文件很大，在某些情况下需要许可协议(例如Helvetica，一种Linotype字体)。

EDIT

The Android design language relies on traditional typographic tools such as scale, space, rhythm, and alignment with an underlying grid. Successful deployment of these tools is essential to help users quickly understand a screen of information. To support such use of typography, Ice Cream Sandwich introduced a new type family named Roboto, created specifically for the requirements of UI and high-resolution screens. The current TextView framework offers Roboto in thin, light, regular and bold weights, along with an italic style for each weight. The framework also offers the Roboto Condensed variant in regular and bold weights, along with an italic style for each weight.

ICS之后，android包含了Roboto字体样式， 阅读更多Roboto

编辑2

随着支持库26的出现，Android现在支持自定义字体 违约。您可以在res/fonts中插入新的字体，这些字体可以单独以XML或编程方式设置为TextViews。整个应用程序的默认字体也可以通过定义它styles.xml来改变，android开发者文档对此有明确的指导

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);

也许可以简单一点:

public class Fonts {
  public static HashSet<String,Typeface> fonts = new HashSet<>();

  public static Typeface get(Context context, String file) {
    if (! fonts.contains(file)) {
      synchronized (this) {
        Typeface typeface = Typeface.createFromAsset(context.getAssets(), name);
        fonts.put(name, typeface);
      }
    }
    return fonts.get(file);
  }
}

// Usage
Typeface myFont = Fonts.get("arial.ttf");

(请注意，此代码未经测试，但通常这种方法应该工作良好。)

另一种巩固字体创建的方法…

public class Font {
  public static final Font  PROXIMA_NOVA    = new Font("ProximaNovaRegular.otf");
  public static final Font  FRANKLIN_GOTHIC = new Font("FranklinGothicURWBoo.ttf");
  private final String      assetName;
  private volatile Typeface typeface;

  private Font(String assetName) {
    this.assetName = assetName;
  }

  public void apply(Context context, TextView textView) {
    if (typeface == null) {
      synchronized (this) {
        if (typeface == null) {
          typeface = Typeface.createFromAsset(context.getAssets(), assetName);
        }
      }
    }
    textView.setTypeface(typeface);
  }
}

然后在你的活动中使用…

myTextView = (TextView) findViewById(R.id.myTextView);
Font.PROXIMA_NOVA.apply(this, myTextView);

请注意，这种带有volatile字段的双重检查锁定习惯用法仅适用于Java 1.5+中使用的内存模型。