Android 将view 转换为Bitmap出现空指针问题解决办法

/**
   * 将View(布局) 转换为bitmap
   * @param view
   * @return
   */
  public static Bitmap createBitmap(View view){
    view.setDrawingCacheEnabled(true);
    /**
     * 这里要注意，在用View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED)
     * 来测量view 的时候,（如果你的布局中包含有 RelativeLayout ）API 为17 或者 低于17 会包空指针异常
     * 解决方法:
     * 1 布局中不要包含RelativeLayout
     * 2 用 View.MeasureSpec.makeMeasureSpec(256, View.MeasureSpec.EXACTLY) 好像也可以
     *
     */
    view.measure(View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED),
        View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
    view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight());
    view.buildDrawingCache();
    Bitmap bitmap = view.getDrawingCache();
    return bitmap;
  }

/**
     * Creates a measure specification based on the supplied size and mode.
     *
     * The mode must always be one of the following:
     * <ul 
     * <li {@link android.view.View.MeasureSpec#UNSPECIFIED}</li 
     * <li {@link android.view.View.MeasureSpec#EXACTLY}</li 
     * <li {@link android.view.View.MeasureSpec#AT_MOST}</li 
     * </ul 
     *
     * <p <strong Note:</strong  On API level 17 and lower, makeMeasureSpec's
     * implementation was such that the order of arguments did not matter
     * and overflow in either value could impact the resulting MeasureSpec.
     * {@link android.widget.RelativeLayout} was affected by this bug.
     * Apps targeting API levels greater than 17 will get the fixed, more strict
     * behavior.</p 
     *
     * @param size the size of the measure specification
     * @param mode the mode of the measure specification
     * @return the measure specification based on size and mode
     */
    public static int makeMeasureSpec(int size, int mode) {
      if (sUseBrokenMakeMeasureSpec) {
        return size + mode;
      } else {
        return (size & ~MODE_MASK) | (mode & MODE_MASK);
      }
    }