1、增加类型转换扩展方法：toIntOrNull、toDoubleOrNull(返回可null的int、double)

lib/common/extension.dart

@@ -62,6 +62,17 @@ extension StringExt on String? {
     }
   }
 
+  int? toIntOrNull() {
+    if (isNullOrEmpty()) {
+      return null;
+    }
+    try {
+      return int.parse(this!);
+    } catch (e) {
+      return null;
+    }
+  }
+
   double toDouble() {
     if (isNullOrEmpty()) {
       return 0.0;
@@ -73,6 +84,17 @@ extension StringExt on String? {
     }
   }
 
+  double? toDoubleOrNull() {
+    if (isNullOrEmpty()) {
+      return null;
+    }
+    try {
+      return double.parse(this!);
+    } catch (e) {
+      return null;
+    }
+  }
+
 }
 
 /// num 扩展函数