一、Android屏幕知识

Android项目中的drawable文件夹可分为（4K分辨率不普及、暂时不管）：

|drawable-ldpi | drawable-mdpi | drawable-hdpi | drawable-xhdpi | drawable-xxhdpi | drawable-xxxhdpi
---|---|---|---|---|---|----
对应 | ldpi | mdpi | hdpi | xhdpi | xxhdpi | xxxhdpi【2K】
屏幕DPI值 | 120 | 160 | 240 | 320 | 480 | 640
屏幕分辨率 | 240x320 | 320x480 | 480x800 | 720x1280 | 1080x1920 | 1440x2560
相对比例 | 3 | 4 | 6 | 8 | 12 | 16
1dp等于 | 0.75px | 1px（基准） | 1.5px | 2px | 3px | 4px

二、开发常用的屏幕DP和PX、SP和PX的相互转换工具类

import android.app.Activity;
import android.util.DisplayMetrics;

import java.util.HashMap;
import java.util.Map;

/**
 * 屏幕显示相关工具类
 * （px ，sp， dp 等转换）
 * Created by JP on 2016/4/7.
 */
public class DisplayUtil {

    private static Map<ScreenEnum,Integer> screenMap = new HashMap<>();

    /**
     * 将px值转换为dip或dp值，保证尺寸大小不变
     *
     * @param pxValue
     * @return
     */
    public static int px2dip(float pxValue, Activity activity) {

        return (int) (pxValue / getScreenMsg(activity).get(ScreenEnum.Density) + 0.5f);
    }
    /**
     * 将dip或dp值转换为px值，保证尺寸大小不变
     * @return
     */
    public static int dip2px(float dipValue, Activity activity) {
        return (int) (dipValue * getScreenMsg(activity).get(ScreenEnum.Density) + 0.5f);
    }
    /**
     * 将px值转换为sp值，保证文字大小不变
     *
     * @return
     */
    public static int px2sp(float pxValue, Activity activity) {
        return (int) (pxValue / getScreenMsg(activity).get(ScreenEnum.ScaledDensity) + 0.5f);
    }
    /**
     * 将sp值转换为px值，保证文字大小不变
     * @return
     */
    public static int sp2px(float spValue, Activity activity) {
        return (int) (spValue * getScreenMsg(activity).get(ScreenEnum.ScaledDensity) + 0.5f);
    }
    /**
     * 获取屏幕尺寸等信息
     */
    public static Map<ScreenEnum,Integer> getScreenMsg(Activity activity){
        DisplayMetrics metric = new DisplayMetrics();
        activity.getWindowManager().getDefaultDisplay().getMetrics(metric);
        int width = metric.widthPixels;
        int height = metric.heightPixels;
        float density = metric.density;///屏幕密度（0.75, 1.0 . 1.5）
        int densityDpi = metric.densityDpi;///屏幕密度DPI（120/160/240/320/480）
        float scaledDensity = metric.scaledDensity;
        if (screenMap==null) screenMap = new HashMap<>();

        screenMap.clear();
        screenMap.put(ScreenEnum.Width,width);
        screenMap.put(ScreenEnum.Height,height);
        screenMap.put(ScreenEnum.Density,(int)density);
        screenMap.put(ScreenEnum.DendityDpi,densityDpi);
        screenMap.put(ScreenEnum.ScaledDensity, (int)scaledDensity);
        return screenMap;
    }

    enum ScreenEnum{
        Width,Height,Density,DendityDpi,ScaledDensity
    }
}