Android DisplayMetrics 擷取和螢幕相關的資訊

標籤：

Android源碼中是這樣來描述DisplayMetrics的。

/** * 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> */

按照DisplayMetrics注釋中的那樣，我們直接寫個例子來測試下，就什麼都明白了。我用的是小米3：

        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 是邏輯上的螢幕密度，約定在160dpi的裝置上，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 表示每英寸的點數（並不是像素數）         */        int densityDpi = metrics.densityDpi;        /**         * The absolute height of the display in pixels.         * 螢幕的絕對高度，以像素為單位。         */        int heightPixels = metrics.heightPixels;        /**         * The absolute width of the display in pixels.         * 同樣，這個是螢幕的絕對寬度，以像素為單位。         */        int widthPixels = metrics.widthPixels;        /**         * The exact physical pixels per inch of the screen in the X dimension.         * 橫向每一英寸確切的物理像素，我們可以嘗試通過這個值和widthPixels 來計算螢幕的寬度英寸。         */        float xdpi = metrics.xdpi;        /**         * The exact physical pixels per inch of the screen in the Y dimension.         * 橫向每一英寸確切的物理像素，我們可以嘗試通過這個值和heightPixels 來計算螢幕的高度英寸。         */        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 這個值從上面的注釋看，是和字型相關的factor，通常情況下這個值和density是相等的，但是假如使用者手動的調整了         *  系統字型的大小，那麼這個值就有可能改變（以小米3為例，標準字型，這個值=3，最大字型這個值=3.25）。         *  因此現在很多情況下，我們把字型單位寫成dp，儘管Google建議的字型讓寫成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);        //來計算手機是幾英寸的        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);

通過這個例子，我們明白了dip及px代表著什麼，我們就可以來寫出dip與px相互轉換的方法。（dip = px / density）

    /**     * 根據手機的解析度從 dp 的單位 轉成為 px(像素)     */    public static int dip2px(Context context, float dpValue) {        final float scale = context.getResources().getDisplayMetrics().density;        return (int) (dpValue * scale + 0.5f);    }    /**     * 根據手機的解析度從 px(像素) 的單位 轉成為 dp     */    public static int px2dip(Context context, float pxValue) {        final float scale = context.getResources().getDisplayMetrics().density;        return (int) (pxValue / scale + 0.5f);    }

上面 加的這個0.5f的原因，Google官方文檔中其實有介紹：

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

說白了就是為了四捨五入。。。

比如我上面的例子：

mobileInch = 4.917646062686045 ，我+0.5f（=5.417646062686045），然後再取整之後，就得到5。

 

Android DisplayMetrics 擷取和螢幕相關的資訊