textView.setTextSize(textSize);

<dimen name="text_size">16sp</dimen>

float dimen = getResources().getDimension(R.dimen.text_size);
textView.setTextSize(dimen);

  /**
   * Retrieve a dimensional for a particular resource ID. Unit 
   * conversions are based on the current {@link DisplayMetrics} associated
   * with the resources.
   * 
   * @param id The desired resource identifier, as generated by the aapt
   *      tool. This integer encodes the package, type, and resource
   *      entry. The value 0 is an invalid identifier.
   * 
   * @return Resource dimension value multiplied by the appropriate 
   * metric.
   */
  public float getDimension(@DimenRes int id) throws NotFoundException {   
  }

  /**
   * Retrieve a dimensional for a particular resource ID for use
   * as a size in raw pixels. This is the same as
   * {@link #getDimension}, except the returned value is converted to
   * integer pixels for use as a size. A size conversion involves
   * rounding the base value, and ensuring that a non-zero base value
   * is at least one pixel in size.
   * 
   * @param id The desired resource identifier, as generated by the aapt
   *      tool. This integer encodes the package, type, and resource
   *      entry. The value 0 is an invalid identifier.
   * 
   * @return Resource dimension value multiplied by the appropriate 
   * metric and truncated to integer pixels.
   */
  public int getDimensionPixelSize(@DimenRes int id) throws NotFoundException {
 
  }

  /**
   * Retrieve a dimensional for a particular resource ID for use
   * as an offset in raw pixels. This is the same as
   * {@link #getDimension}, except the returned value is converted to
   * integer pixels for you. An offset conversion involves simply
   * truncating the base value to an integer.
   * 
   * @param id The desired resource identifier, as generated by the aapt
   *      tool. This integer encodes the package, type, and resource
   *      entry. The value 0 is an invalid identifier.
   * 
   * @return Resource dimension value multiplied by the appropriate 
   * metric and truncated to integer pixels.
   */
  public int getDimensionPixelOffset(@DimenRes int id) throws NotFoundException {
  }

 public float getDimension(@DimenRes int id) throws NotFoundException {
    final TypedValue value = obtainTempTypedValue();
    try {
      final ResourcesImpl impl = mResourcesImpl;
      impl.getValue(id, value, true);
      if (value.type == TypedValue.TYPE_DIMENSION) {
        return TypedValue.complexToDimension(value.data, impl.getDisplayMetrics());
      }
      throw new NotFoundException("Resource ID #0x" + Integer.toHexString(id)
          + " type #0x" + Integer.toHexString(value.type) + " is not valid");
    } finally {
      releaseTempTypedValue(value);
    }
  }

  public static float complexToDimension(int data, DisplayMetrics metrics) {
    return applyDimension(
      (data>>COMPLEX_UNIT_SHIFT)&COMPLEX_UNIT_MASK,
      complexToFloat(data),
      metrics);
  }

public static float applyDimension(int unit, float value,DisplayMetrics metrics) {
    switch (unit) {
    case COMPLEX_UNIT_PX:
      return value;
    case COMPLEX_UNIT_DIP:
      return value * metrics.density;
    case COMPLEX_UNIT_SP:
      return value * metrics.scaledDensity;
    case COMPLEX_UNIT_PT:
      return value * metrics.xdpi * (1.0f/72);
    case COMPLEX_UNIT_IN:
      return value * metrics.xdpi;
    case COMPLEX_UNIT_MM:
      return value * metrics.xdpi * (1.0f/25.4f);
    }
    return 0;
  }

 public void setTextSize(float size) {
    setTextSize(TypedValue.COMPLEX_UNIT_SP, size);
  }

  public void setTextSize(int unit, float size) {
    if (!isAutoSizeEnabled()) {
      setTextSizeInternal(unit, size, true /* shouldRequestLayout */);
    }
  }

  private void setTextSizeInternal(int unit, float size, boolean shouldRequestLayout) {
    Context c = getContext();
    Resources r;
    if (c == null) {
      r = Resources.getSystem();
    } else {
      r = c.getResources();
    }
    setRawTextSize(TypedValue.applyDimension(unit, size, r.getDisplayMetrics()),shouldRequestLayout);
  }

int dimen = getResources().getDimensionPixelSize(R.dimen.text_size);
textView.setTextSize(TypedValue.COMPLEX_UNIT_PX，dimen);