FloatingActionButton with text instead of image

With API 28 you can simply add text to Fabs using:

Visit: https://material.io/develop/android/components/extended-floating-action-button/

 <com.google.android.material.floatingactionbutton.ExtendedFloatingActionButton
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_margin="8dp"
      android:contentDescription="@string/extended_fab_content_desc"
      android:text="@string/extended_fab_label"
      app:icon="@drawable/ic_plus_24px"
      app:layout_anchor="@id/app_bar"
      app:layout_anchorGravity="bottom|right|end"/>

FABs are usually used in CoordinatorLayouts. You can use this:

<android.support.design.widget.CoordinatorLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto">

    <android.support.design.widget.FloatingActionButton
            android:id="@+id/fab"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom|end"
            android:layout_margin="@dimen/fab_margin"               
            app:backgroundTint="@color/colorPrimary" />

      <TextView android:layout_height="wrap_content"
              android:layout_width="wrap_content"
              android:text="OK"
              android:elevation="6dp"
              android:textSize="18dp"
              android:textColor="#fff"
              app:layout_anchor="@id/fab"
              app:layout_anchorGravity="center"/>

</android.support.design.widget.CoordinatorLayout>

This is what does the work

app:layout_anchor="@id/fab"
app:layout_anchorGravity="center"

Result:

If you're using some layout_behavior for your FAB, you'll have to make a similar layout_behavior for the TextView

convert a text into bitmap and use it. its super easy.

fab.setImageBitmap(textAsBitmap("OK", 40, Color.WHITE));

//method to convert your text to image
public static Bitmap textAsBitmap(String text, float textSize, int textColor) {
    Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    paint.setTextSize(textSize);
    paint.setColor(textColor);
    paint.setTextAlign(Paint.Align.LEFT);
    float baseline = -paint.ascent(); // ascent() is negative
    int width = (int) (paint.measureText(text) + 0.0f); // round
    int height = (int) (baseline + paint.descent() + 0.0f);
    Bitmap image = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);

    Canvas canvas = new Canvas(image);
    canvas.drawText(text, 0, baseline, paint);
    return image;
}

Thanks to all.

Here is easy workaround which I found for this question. Works correctly for Android 4+, for Android 5+ is added specific parameter android:elevation to draw TextView over FloatingActionButton.

<FrameLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|right">

    <android.support.design.widget.FloatingActionButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@android:color/transparent" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="@android:string/ok"
        android:elevation="16dp"
        android:textColor="@android:color/white"
        android:textAppearance="?android:attr/textAppearanceMedium" />
</FrameLayout>