diff --git a/app/src/main/java/io/legado/app/data/entities/BaseBook.kt b/app/src/main/java/io/legado/app/data/entities/BaseBook.kt
index 62d322b6c..31346a50c 100644
--- a/app/src/main/java/io/legado/app/data/entities/BaseBook.kt
+++ b/app/src/main/java/io/legado/app/data/entities/BaseBook.kt
@@ -4,7 +4,7 @@ import io.legado.app.utils.splitNotBlank
 
 interface BaseBook {
     var bookUrl: String
-    var variableMap: HashMap<String, String>?
+    val variableMap: HashMap<String, String>
     var kind: String?
     var wordCount: String?
 
diff --git a/app/src/main/java/io/legado/app/data/entities/Book.kt b/app/src/main/java/io/legado/app/data/entities/Book.kt
index fd96d137b..1bb69ea81 100644
--- a/app/src/main/java/io/legado/app/data/entities/Book.kt
+++ b/app/src/main/java/io/legado/app/data/entities/Book.kt
@@ -71,15 +71,16 @@ data class Book(
         return bookUrl.hashCode()
     }
 
-    @Ignore
+    @delegate:Ignore
     @IgnoredOnParcel
-    override var variableMap: HashMap<String, String>? = null
-        get() {
-            if (field == null) {
-                field = GSON.fromJsonObject<HashMap<String, String>>(variable) ?: HashMap()
-            }
-            return field
-        }
+    override val variableMap by lazy {
+        GSON.fromJsonObject<HashMap<String, String>>(variable) ?: HashMap()
+    }
+
+    override fun putVariable(key: String, value: String) {
+        variableMap[key] = value
+        variable = GSON.toJson(variableMap)
+    }
 
     @Ignore
     @IgnoredOnParcel
@@ -97,11 +98,6 @@ data class Book(
 
     fun getDisplayIntro() = if (customIntro.isNullOrEmpty()) intro else customIntro
 
-    override fun putVariable(key: String, value: String) {
-        variableMap?.put(key, value)
-        variable = GSON.toJson(variableMap)
-    }
-
     fun fileCharset(): Charset {
         return charset(charset ?: "UTF-8")
     }
diff --git a/app/src/main/java/io/legado/app/data/entities/SearchBook.kt b/app/src/main/java/io/legado/app/data/entities/SearchBook.kt
index 27f666547..72cdb721d 100644
--- a/app/src/main/java/io/legado/app/data/entities/SearchBook.kt
+++ b/app/src/main/java/io/legado/app/data/entities/SearchBook.kt
@@ -63,18 +63,14 @@ data class SearchBook(
         return other.originOrder - this.originOrder
     }
 
-    @Ignore
+    @delegate:Ignore
     @IgnoredOnParcel
-    override var variableMap: HashMap<String, String>? = null
-        get() {
-            if (field == null) {
-                field = GSON.fromJsonObject<HashMap<String, String>>(variable) ?: HashMap()
-            }
-            return field
-        }
+    override val variableMap by lazy {
+        GSON.fromJsonObject<HashMap<String, String>>(variable) ?: HashMap()
+    }
 
     override fun putVariable(key: String, value: String) {
-        variableMap?.put(key, value)
+        variableMap[key] = value
         variable = GSON.toJson(variableMap)
     }