/**

 * A structure describing general information about a display, such as its

 * size, density, and font scaling.

 * <p>To access the DisplayMetrics members, initialize an object like this:</p>

 * <pre> DisplayMetrics metrics = new DisplayMetrics();

 * getWindowManager().getDefaultDisplay().getMetrics(metrics);</pre>

 */

        DisplayMetrics metrics = new DisplayMetrics();

        getActivity().getWindowManager().getDefaultDisplay().getMetrics(metrics);

        /**

         * The logical density of the display.  This is a scaling factor for the

         * Density Independent Pixel unit, where one DIP is one pixel on an

         * approximately 160 dpi screen (for example a 240x320, 1.5"x2" screen),

         * providing the baseline of the system's display. Thus on a 160dpi screen

         * this density value will be 1; on a 120 dpi screen it would be .75; etc.

         *

         * <p>This value does not exactly follow the real screen size (as given by

         * {@link #xdpi} and {@link #ydpi}, but rather is used to scale the size of

         * the overall UI in steps based on gross changes in the display dpi.  For

         * example, a 240x320 screen will have a density of 1 even if its width is

         * 1.8", 1.3", etc. However, if the screen resolution is increased to

         * 320x480 but the screen size remained 1.5"x2" then the density would be

         * increased (probably to 1.5).

         *

         * density 是逻辑上的屏幕密度，约定在160dpi的设备上，1px=1dip。

         * density = densityDpi / 160

         *

         * @see #DENSITY_DEFAULT

         */

        float density = metrics.density;

        /**

         * The screen density expressed as dots-per-inch.  May be either

         * {@link #DENSITY_LOW}, {@link #DENSITY_MEDIUM}, or {@link #DENSITY_HIGH}.

         * densityDpi 表示每英寸的点数（并不是像素数）

         */

        int densityDpi = metrics.densityDpi;

        /**

         * The absolute height of the display in pixels.

         * 屏幕的绝对高度，以像素为单位。

         */

        int heightPixels = metrics.heightPixels;

        /**

         * The absolute width of the display in pixels.

         * 同样，这个是屏幕的绝对宽度，以像素为单位。

         */

        int widthPixels = metrics.widthPixels;

        /**

         * The exact physical pixels per inch of the screen in the X dimension.

         * 横向每一英寸确切的物理像素，我们可以尝试通过这个值和widthPixels 来计算屏幕的宽度英寸。

         */

        float xdpi = metrics.xdpi;

        /**

         * The exact physical pixels per inch of the screen in the Y dimension.

         * 横向每一英寸确切的物理像素，我们可以尝试通过这个值和heightPixels 来计算屏幕的高度英寸。

         */

        float ydpi = metrics.ydpi;

        /**

         * A scaling factor for fonts displayed on the display.  This is the same

         * as {@link #density}, except that it may be adjusted in smaller

         * increments at runtime based on a user preference for the font size.

         *  scaledDensity 这个值从上面的注释看，是和字体相关的factor，通常情况下这个值和density是相等的，但是假如用户手动的调整了

         *  系统字体的大小，那么这个值就有可能改变（以小米3为例，标准字体，这个值=3，最大字体这个值=3.25）。

         *  因此现在很多情况下，我们把字体单位写成dp，尽管Google建议的字体让写成sp。

         */

        float scaledDensity = metrics.scaledDensity;

        LogUtil.logd(TAG, "metrics.density = " + density);

        LogUtil.logd(TAG, "metrics.densityDpi = " + densityDpi);

        LogUtil.logd(TAG, "metrics.heightPixels = " +heightPixels);

        LogUtil.logd(TAG, "metrics.widthPixels = " +widthPixels);

        LogUtil.logd(TAG, "metrics.xdpi = " +xdpi);

        LogUtil.logd(TAG, "metrics.ydpi = " +ydpi);

        LogUtil.logd(TAG, "metrics.scaledDensity = " +scaledDensity);

        //来计算手机是几英寸的

        float pixelsToDipWidth  = widthPixels / xdpi;

        float pixelsToDipHeight = heightPixels / ydpi;

        LogUtil.logd(TAG, "pixelsToDipWidth = " + pixelsToDipWidth);

        LogUtil.logd(TAG, "pixelsToDipHeight = " + pixelsToDipHeight);

        double mobileInch = Math.sqrt(pixelsToDipHeight * pixelsToDipHeight + pixelsToDipWidth * pixelsToDipWidth);

        //我用的小米3，得到的值是4.917646062686045

        LogUtil.logd(TAG, "mobileInch = " + mobileInch);

    /**

     * 根据手机的分辨率从 dp 的单位 转成为 px(像素)

     */

    public static int dip2px(Context context, float dpValue) {

        final float scale = context.getResources().getDisplayMetrics().density;

        return (int) (dpValue * scale + 0.5f);

    }

    /**

     * 根据手机的分辨率从 px(像素) 的单位 转成为 dp

     */

    public static int px2dip(Context context, float pxValue) {

        final float scale = context.getResources().getDisplayMetrics().density;

        return (int) (pxValue / scale + 0.5f);

    }

Then add 0.5f to round the figure up to the nearest whole number, when converting to an integer.