1. dp , px 的转化 sp，px 的转化

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public class PxUtil {

    /**
     * 得到设备的密度
     */
    public static float getScreenDensity(Context context) {
        return context.getResources().getDisplayMetrics().density;
    }

    /**
     * 将传递的 整型dp 值转化为 px
     * @param dp
     * @param context
     * @return
     */
    public static int dpToPx(int dp, Context context){
        return (int) (dp * getScreenDensity(context));
    }

    /**
     * 将传递的 浮点型dp 值转化为 px
     * @param dp
     * @param context
     * @return
     */
    public static int dpToPx(float dp, Context context){
        return (int) (dp * getScreenDensity(context));
    }

    /**
     * 将传递的 整型px 值转化为 dp
     * @param px
     * @param context
     * @return
     */
    public static float pxToDp(int px, Context context){
        return  (px / getScreenDensity(context));
    }

    /**
     * 将传递的 浮点型px 值转化为 dp
     * @param px
     * @param context
     * @return
     */
    public static float pxToDp(float px, Context context){
        return  (px / getScreenDensity(context));
    }

    /**
     * 将传递的 sp 值转化为 px
     * @param sp
     * @param context
     * @return
     */
    public static int spToPx(int sp, Context context){
        return (int) (sp * getScreenDensity(context));
    }

    /**
     * 将传递的 px 值 转化为 sp
     * @param px
     * @param context
     * @return
     */
    public static int pxToSp(int px, Context context){
        return (int) (px / getScreenDensity(context));
    }
}

2. 屏幕宽度，高度，状态栏高度，导航栏高度

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public class ScreenUtil {
    /**
     * 获取屏幕的宽度
     * @param context
     * @return
     */
    public static int getScreenWidth(Context context){
        //窗口管理者
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        //存储尺寸的
        DisplayMetrics displayMetrics = new DisplayMetrics();
        //获取尺寸
        assert windowManager != null;
        windowManager.getDefaultDisplay().getRealMetrics(displayMetrics);

        return displayMetrics.widthPixels;
    }

    /**
     * 获取屏幕的高度
     * @param context
     * @return
     */
    public static int getScreenHeight(Context context){
        //窗口管理者
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        //存储尺寸的
        DisplayMetrics displayMetrics = new DisplayMetrics();
        //获取尺寸
        assert windowManager != null;
        windowManager.getDefaultDisplay().getRealMetrics(displayMetrics);

        return displayMetrics.heightPixels;
    }

    /**
     * 获取StatusBar状态栏的高度
     * @param context
     * @return
     */
    public static int getStateBarHeight(Context context){
        int statusHeight = -1;
        try {
            Class clazz = Class.forName("com.android.internal.R$dimen");
            Object object = clazz.newInstance();
            int height = Integer.parseInt(clazz.getField("status_bar_height")
                    .get(object).toString());
            statusHeight = context.getResources().getDimensionPixelSize(height);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return statusHeight;
    }

    /**
     * 判断设置是否有NavigationBar导航栏
     * @param context
     * @return
     */
    private static boolean checkDeviceHasNavigationBar(Context context) {
        boolean hasNavigationBar = false;
        Resources rs = context.getResources();
        int id = rs.getIdentifier("config_showNavigationBar", "bool", "android");
        if (id > 0) {
            hasNavigationBar = rs.getBoolean(id);
        }
        try {
            Class systemPropertiesClass = Class.forName("android.os.SystemProperties");
            Method m = systemPropertiesClass.getMethod("get", String.class);
            String navBarOverride = (String) m.invoke(systemPropertiesClass, "qemu.hw.mainkeys");
            if ("1".equals(navBarOverride)) {
                hasNavigationBar = false;
            } else if ("0".equals(navBarOverride)) {
                hasNavigationBar = true;
            }
        } catch (Exception e) {

        }

        return hasNavigationBar;
    }

    /**
     * 返回NavigationBar导航栏的高度
     * @param context
     * @return
     */
    public static int getNavigationBarHeight(Context context) {
        int height = 0;

        //如果存在
        if (ScreenUtil.checkDeviceHasNavigationBar(context)){
            Resources resources = context.getResources();
            int resourceId = resources.getIdentifier("navigation_bar_height","dimen", "android");
            height = resources.getDimensionPixelSize(resourceId);
            Log.v("dbw", "Navi height:" + height);
        }

        return height;
    }

}

3. 程序是否在后台

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public class StateUtil {

    /**
     * 判断是否在前台
     * @param context
     * @return
     */
    public static boolean isBackground(Context context) {
        ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
        List<ActivityManager.RunningAppProcessInfo> appProcesses = activityManager.getRunningAppProcesses();
        for (ActivityManager.RunningAppProcessInfo appProcess : appProcesses) {
            if (appProcess.processName.equals(context.getPackageName())) {
                if (appProcess.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_BACKGROUND) {
                    Log.i("后台", appProcess.processName);
                    return true;
                }else{
                    Log.i("前台", appProcess.processName);
                    return false;
                }
            }
        }

        return false;
    }
}

4. 将一个bitmap保存到系统相册中

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public class SaveToAlbumUtil {
    /**
     * 将一个bitmap保存到系统相册中
     * @param bitmap
     * @param picName
     * @param context
     */
    public static void saveBitmapToGallery(Bitmap bitmap, String picName, Context context) {

        String fileName = null;
        //系统相册目录
        String galleryPath= Environment.getExternalStorageDirectory()
                + File.separator + Environment.DIRECTORY_DCIM
                +File.separator+"Camera"+File.separator;

        // 声明文件对象
        File file = null;
        // 声明输出流
        FileOutputStream outStream = null;

        try {
            // 如果有目标文件，直接获得文件对象，否则创建一个以filename为名称的文件
            file = new File(galleryPath, picName+ ".jpeg");

            // 获得文件相对路径
            fileName = file.toString();
            // 获得输出流，如果文件中有内容，追加内容
            outStream = new FileOutputStream(fileName);
            bitmap.compress(Bitmap.CompressFormat.JPEG, 90, outStream);

        } catch (Exception e) {
            e.getStackTrace();
        }finally {
            //释放资源
            try {
                if (outStream != null) {
                    outStream.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        //将图片插入到系统相册中
        MediaStore.Images.Media.insertImage(context.getContentResolver(),
                bitmap, fileName, null);

        //通知相册更新
        Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        Uri uri = Uri.fromFile(file);
        intent.setData(uri);
        context.sendBroadcast(intent);

        //信息提示
        Toast.makeText(context, "图片保存成功", Toast.LENGTH_SHORT).show();
    }
}