Android 整个应用换字体，字体ttf 文件放到 assets 下，调用可以放到 Application 的 onCreate 里面

ChangeFont

private void setDefaultFont() {
  	try {
			final Typeface bold = Typeface.createFromAsset(getAssets(),
					"stheitilight.ttf");
			final Typeface italic = Typeface.createFromAsset(getAssets(),
					"stheitilight.ttf");
			final Typeface boldItalic = Typeface.createFromAsset(getAssets(),
					"stheitilight.ttf");
			final Typeface regular = Typeface.createFromAsset(getAssets(),
					"stheitilight.ttf");

			Field DEFAULT = Typeface.class.getDeclaredField("DEFAULT");
			DEFAULT.setAccessible(true);
			DEFAULT.set(null, regular);

			Field DEFAULT_BOLD = Typeface.class
					.getDeclaredField("DEFAULT_BOLD");
			DEFAULT_BOLD.setAccessible(true);
			DEFAULT_BOLD.set(null, bold);

			Field sDefaults = Typeface.class.getDeclaredField("sDefaults");
			sDefaults.setAccessible(true);
			sDefaults.set(null, new Typeface[] { regular, bold, italic,
					boldItalic });

		} catch (Throwable e) {
			e.printStackTrace();
		}
	}

gistfile1.java

修改 ActionBar 的字体：
try {
Integer titleId = (Integer) Class.forName("com.android.internal.R$id")
.getField("action_bar_title").get(null);
TextView title = (TextView) getWindow().findViewById(titleId);
// check for null and manipulate the title as see fit
} catch (Exception e) {
Log.e(TAG, "Failed to obtain action bar title reference");
}

P.S. Based on @pjv comment there's a better way to find action bar title id

final int titleId = 
Resources.getSystem().getIdentifier("action_bar_title", "id", "android");

new_gist_file

@Override
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
    View view = super.onCreateView(parent, name, context, attrs);
    return setCustomTypeFaceIfNeeded(name, attrs, view);
}

protected View setCustomTypeFaceIfNeeded(String name, AttributeSet attrs, View view) {
    View result = null;
    if ("TextView".equals(name)) {
        result = new TextView(this, attrs);
        ((TextView) result).setTypeface(helloTypeface);
    }

    if ("EditText".equals(name)) {
        result = new EditText(this, attrs);
        ((EditText) result).setTypeface(helloTypeface);
    }

    if ("Button".equals(name)) {
        result = new Button(this, attrs);
        ((Button) result).setTypeface(helloTypeface);
    }

    if (result == null) {
        return view;
    } else {
        if (ENABLE_FONT_LOGGING) {
            Log.v(FONT_LOG_CAT_TAG, "A type face was set on " + result.getId());
        }
        return result;
    }
}

这个要奏效一点

@OverRide
public View onCreateView(String name, Context context, AttributeSet attrs) {
View view = super.onCreateView(name, context, attrs);
return setCustomTypeFaceIfNeeded(name, attrs, view);
}

@Override
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
    View view = super.onCreateView(parent, name, context, attrs);
    return setCustomTypeFaceIfNeeded(name, attrs, view);
}

protected View setCustomTypeFaceIfNeeded(String name, AttributeSet attrs, View view) {
    View result = null;
    if ("TextView".equals(name)) {
        result = new TextView(this, attrs);
        ((TextView) result).setTypeface(helloTypeface);
    }

    if ("EditText".equals(name)) {
        result = new EditText(this, attrs);
        ((EditText) result).setTypeface(helloTypeface);
    }

    if ("Button".equals(name)) {
        result = new Button(this, attrs);
        ((Button) result).setTypeface(helloTypeface);
    }

    if (result == null) {
        return view;
    } else {
        if (ENABLE_FONT_LOGGING) {
            Log.v(FONT_LOG_CAT_TAG, "A type face was set on " + result.getId());
        }
        return result;
    }
}

修改 ActionBar 的字体：
try {
Integer titleId = (Integer) Class.forName("com.android.internal.R$id")
.getField("action_bar_title").get(null);
TextView title = (TextView) getWindow().findViewById(titleId);
// check for null and manipulate the title as see fit
} catch (Exception e) {
Log.e(TAG, "Failed to obtain action bar title reference");
}

P.S. Based on @pjv comment there's a better way to find action bar title id

final int titleId =
Resources.getSystem().getIdentifier("action_bar_title", "id", "android");