Android中dpi 和density到底是什么关系？

源码：

/frameworks/base/core/java/android/util/DisplayMetrics.java

194 /**195 * The logical density of the display. This is a scaling factor for the196 * Density Independent Pixel unit, where one DIP is one pixel on an197 * approximately 160 dpi screen (for example a 240x320, 1.5"x2" screen),198 * providing the baseline of the system's display. Thus on a 160dpi screen199 * this density value will be 1; on a 120 dpi screen it would be .75; etc.200 *201 *

This value does not exactly follow the real screen size (as given by202 * {@link #xdpi} and {@link #ydpi}, but rather is used to scale the size of203 * the overall UI in steps based on gross changes in the display dpi. For204 * example, a 240x320 screen will have a density of 1 even if its width is205 * 1.8", 1.3", etc. However, if the screen resolution is increased to206 * 320x480 but the screen size remained 1.5"x2" then the density would be207 * increased (probably to 1.5).208 *209 * @see #DENSITY_DEFAULT210 */211 public float density;

默认：

299    public void setToDefaults() {300        widthPixels = 0;301        heightPixels = 0;302        density =  DENSITY_DEVICE / (float) DENSITY_DEFAULT;303        densityDpi =  DENSITY_DEVICE;304        scaledDensity = density;305        xdpi = DENSITY_DEVICE;306        ydpi = DENSITY_DEVICE;307        noncompatWidthPixels = widthPixels;308        noncompatHeightPixels = heightPixels;309        noncompatDensity = density;310        noncompatDensityDpi = densityDpi;311        noncompatScaledDensity = scaledDensity;312        noncompatXdpi = xdpi;313        noncompatYdpi = ydpi;314    }

注释：

默认情况：density = DENSITY_DEVICE / (float) DENSITY_DEFAULT;

DENSITY_DEVICE和DENSITY_DEFAULT在DisplayMetrics.java都有说明：

35    /**36     * Standard quantized DPI for medium-density screens.37     */38    public static final int DENSITY_MEDIUM = 160;...155    public static final int DENSITY_DEFAULT = DENSITY_MEDIUM;...162163    /**164     * The device's current density.165     * 166     * This value reflects any changes made to the device density. To obtain167     * the device's stable density, use {@link #DENSITY_DEVICE_STABLE}.168     *169     * @hide This value should not be used.170     * @deprecated Use {@link #DENSITY_DEVICE_STABLE} to obtain the stable171     *             device density or {@link #densityDpi} to obtain the current172     *             density for a specific display.173     */174    @Deprecated175    public static int DENSITY_DEVICE = getDeviceDensity();...370    private static int getDeviceDensity() {371        // qemu.sf.lcd_density can be used to override ro.sf.lcd_density372        // when running in the emulator, allowing for dynamic configurations.373        // The reason for this is that ro.sf.lcd_density is write-once and is374        // set by the init process when it parses build.prop before anything else.375        return SystemProperties.getInt("qemu.sf.lcd_density",376                SystemProperties.getInt("ro.sf.lcd_density", DENSITY_DEFAULT));377    }

即：dpi为160时，density为1

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