update example,code annotation

Author: 李卓原

example/lib/main.dart

@@ -127,17 +127,17 @@ class _HomePageState extends State<HomePage> {
   }
 
   void printScreenInformation() {
-    print('Device width dp:${1.sw}'); //Device width
-    print('Device height dp:${1.sh}'); //Device height
-    print('Device pixel density:${ScreenUtil().pixelRatio}'); //Device pixel density
+    print('Device width dp:${1.sw}dp');
+    print('Device height dp:${1.sh}dp');
+    print('Device pixel density:${ScreenUtil().pixelRatio}');
     print(
-        'Bottom safe zone distance dp:${ScreenUtil().bottomBarHeight}'); //Bottom safe zone distance，suitable for buttons with full screen
+        'Bottom safe zone distance dp:${ScreenUtil().bottomBarHeight}dp');
     print(
-        'Status bar height px:${ScreenUtil().statusBarHeight}dp'); //Status bar height , Notch will be higher Unit px
+        'Status bar height dp:${ScreenUtil().statusBarHeight}dp');
     print('Ratio of actual width dp to UI Design:${ScreenUtil().scaleWidth}');
     print('Ratio of actual height dp to UI Design:${ScreenUtil().scaleHeight}');
     print('System font scaling:${ScreenUtil().textScaleFactor}');
-    print('0.5 times the screen width:${0.5.sw}');
-    print('0.5 times the screen height:${0.5.sh}');
+    print('0.5 times the screen width:${0.5.sw}dp');
+    print('0.5 times the screen height:${0.5.sh}dp');
   }
 }

example/lib/main_zh.dart

@@ -116,8 +116,8 @@ class _HomePageState extends State<HomePage> {
   }
 
   void printScreenInformation() {
-    print('设备宽度:${1.sw}');
-    print('设备高度:${1.sh}');
+    print('设备宽度:${1.sw}dp');
+    print('设备高度:${1.sh}dp');
     print('设备的像素密度:${ScreenUtil().pixelRatio}');
     print('底部安全区距离:${ScreenUtil().bottomBarHeight}dp');
     print('状态栏高度:${ScreenUtil().statusBarHeight}dp');
@@ -126,7 +126,7 @@ class _HomePageState extends State<HomePage> {
     print('宽度和字体相对于设计稿放大的比例:${ScreenUtil().scaleWidth * ScreenUtil().pixelRatio}');
     print('高度相对于设计稿放大的比例:${ScreenUtil().scaleHeight * ScreenUtil().pixelRatio}');
     print('系统的字体缩放比例:${ScreenUtil().textScaleFactor}');
-    print('屏幕宽度的0.5:${0.5.sw}');
-    print('屏幕高度的0.5:${0.5.sh}');
+    print('屏幕宽度的0.5:${0.5.sw}dp');
+    print('屏幕高度的0.5:${0.5.sh}dp');
   }
 }

lib/screenutil.dart

@@ -79,11 +79,11 @@ class ScreenUtil {
   double get screenHeightPx => _screenHeight * _pixelRatio;
 
   /// 状态栏高度 dp 刘海屏会更高
-  /// The offset from the top
+  /// The offset from the top, in dp
   double get statusBarHeight => _statusBarHeight / _pixelRatio;
 
   /// 底部安全区距离 dp
-  /// The offset from the bottom.
+  /// The offset from the bottom, in dp
   double get bottomBarHeight => _bottomBarHeight / _pixelRatio;
 
   /// 实际的dp与UI设计px的比例