Android 尺寸单位转换和屏幕适配相关

各种尺寸单位的意义

资源类型

尺寸单位转换 工具类

　　可以写工具类对尺寸单位进行转换，比如：

package com.mengdd.dimen;

import android.content.Context;

public class DimenUtils {

    public static int sp2px(Context context, float spValue) {
        float fontScale = context.getResources().getDisplayMetrics().scaledDensity;
        return (int) (spValue * fontScale + 0.5f);
    }

    public static int px2sp(Context context, float pxValue) {
        float fontScale = context.getResources().getDisplayMetrics().scaledDensity;
        return (int) (pxValue / fontScale + 0.5f);
    }

    public static int dip2px(Context context, int dipValue) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (dipValue * scale + 0.5f);
    }

    public static int px2dip(Context context, float pxValue) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (pxValue / scale + 0.5f);
    }
}

　　Android中的DisplayMetrics这个类描述了关于显示的各种信息，可以利用它查看设备的状态，上述关于屏幕密度的标准的常量也是从这个类中看到的。

 　　DisplayMetrics的toString()方法如下：

    @Override
    public String toString() {
        return "DisplayMetrics{density=" + density + ", width=" + widthPixels +
            ", height=" + heightPixels + ", scaledDensity=" + scaledDensity +
            ", xdpi=" + xdpi + ", ydpi=" + ydpi + "}";
    }

　　其中各个变量解释如下：

    /**
     * The absolute width of the display in pixels.
     */
    public int widthPixels;
    /**
     * The absolute height of the display in pixels.
     */
    public int heightPixels;
    /**
     * 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).
     *
     * @see #DENSITY_DEFAULT
     */
    public float density;
    /**
     * The screen density expressed as dots-per-inch.  May be either
     * {@link #DENSITY_LOW}, {@link #DENSITY_MEDIUM}, or {@link #DENSITY_HIGH}.
     */
    public int densityDpi;
    /**
     * 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.
     */
    public float scaledDensity;
    /**
     * The exact physical pixels per inch of the screen in the X dimension.
     */
    public float xdpi;
    /**
     * The exact physical pixels per inch of the screen in the Y dimension.
     */
    public float ydpi;

实际设备参数　

　　小米2S，DisplayMetrics中的toString()方法输出如下：

DisplayMetrics{density=2.0, width=720, height=1280, scaledDensity=2.0, xdpi=345.0566, ydpi=342.23157}

参考资料