diff --git a/app/build.gradle b/app/build.gradle
index 1edcc0755..59657b0f8 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -160,7 +160,7 @@ dependencies {
     testImplementation "androidx.room:room-testing:$room_version"
 
     //paging
-    implementation 'androidx.paging:paging-runtime-ktx:3.0.0'
+    implementation 'androidx.paging:paging-runtime-ktx:2.1.2'
 
     //liveEventBus
     implementation 'com.jeremyliao:live-event-bus-x:1.5.7'
diff --git a/app/src/main/java/io/legado/app/base/BasePreferenceFragment.kt b/app/src/main/java/io/legado/app/base/BasePreferenceFragment.kt
index b2e467b7c..6166b7a5d 100644
--- a/app/src/main/java/io/legado/app/base/BasePreferenceFragment.kt
+++ b/app/src/main/java/io/legado/app/base/BasePreferenceFragment.kt
@@ -54,6 +54,7 @@ abstract class BasePreferenceFragment : PreferenceFragmentCompat() {
             }
         }
         f.setTargetFragment(this, 0)
+
         f.show(parentFragmentManager, dialogFragmentTag)
     }
 
diff --git a/app/src/main/java/io/legado/app/help/JsExtensions.kt b/app/src/main/java/io/legado/app/help/JsExtensions.kt
index 851660fdf..43fcd60a9 100644
--- a/app/src/main/java/io/legado/app/help/JsExtensions.kt
+++ b/app/src/main/java/io/legado/app/help/JsExtensions.kt
@@ -318,7 +318,7 @@ interface JsExtensions {
         if (font1 == null || font2 == null) return text
         val contentArray = text.toCharArray()
         contentArray.forEachIndexed { index, s ->
-            val oldCode = s.toInt()
+            val oldCode = s.code
             if (font1.inLimit(s)) {
                 val code = font2.getCodeByGlyf(font1.getGlyfByCode(oldCode))
                 if (code != 0) contentArray[index] = code.toChar()
diff --git a/app/src/main/java/io/legado/app/model/rss/RssParserByRule.kt b/app/src/main/java/io/legado/app/model/rss/RssParserByRule.kt
index 6affe0b88..1f544425c 100644
--- a/app/src/main/java/io/legado/app/model/rss/RssParserByRule.kt
+++ b/app/src/main/java/io/legado/app/model/rss/RssParserByRule.kt
@@ -51,7 +51,7 @@ object RssParserByRule {
             Debug.log(sourceUrl, "└列表大小:${collections.size}")
             if (!rssSource.ruleNextPage.isNullOrEmpty()) {
                 Debug.log(sourceUrl, "┌获取下一页链接")
-                if (rssSource.ruleNextPage!!.toUpperCase(Locale.getDefault()) == "PAGE") {
+                if (rssSource.ruleNextPage!!.uppercase(Locale.getDefault()) == "PAGE") {
                     nextUrl = sortUrl
                 } else {
                     nextUrl = analyzeRule.getString(rssSource.ruleNextPage)
diff --git a/app/src/main/java/io/legado/app/ui/widget/font/FontSelectDialog.kt b/app/src/main/java/io/legado/app/ui/widget/font/FontSelectDialog.kt
index e4b2d6724..c070e4361 100644
--- a/app/src/main/java/io/legado/app/ui/widget/font/FontSelectDialog.kt
+++ b/app/src/main/java/io/legado/app/ui/widget/font/FontSelectDialog.kt
@@ -141,7 +141,7 @@ class FontSelectDialog : BaseDialogFragment(),
         val fontDir =
             FileUtils.createFolderIfNotExist(requireContext().externalFilesDir, "font")
         fontDir.listFiles { pathName ->
-            pathName.name.toLowerCase(Locale.getDefault()).matches(fontRegex)
+            pathName.name.lowercase(Locale.getDefault()).matches(fontRegex)
         }?.forEach {
             fontItems.add(
                 DocItem(
@@ -161,7 +161,7 @@ class FontSelectDialog : BaseDialogFragment(),
             val fontItems = arrayListOf<DocItem>()
             val docItems = DocumentUtils.listFiles(appCtx, doc.uri)
             docItems.forEach { item ->
-                if (item.name.toLowerCase(Locale.getDefault()).matches(fontRegex)) {
+                if (item.name.lowercase(Locale.getDefault()).matches(fontRegex)) {
                     fontItems.add(item)
                 }
             }
@@ -188,7 +188,7 @@ class FontSelectDialog : BaseDialogFragment(),
             val fontItems = arrayListOf<DocItem>()
             val file = File(path)
             file.listFiles { pathName ->
-                pathName.name.toLowerCase(Locale.getDefault()).matches(fontRegex)
+                pathName.name.lowercase(Locale.getDefault()).matches(fontRegex)
             }?.forEach {
                 fontItems.add(
                     DocItem(
diff --git a/app/src/main/java/io/legado/app/utils/ACache.kt b/app/src/main/java/io/legado/app/utils/ACache.kt
index 5011a713d..934e0b1f1 100644
--- a/app/src/main/java/io/legado/app/utils/ACache.kt
+++ b/app/src/main/java/io/legado/app/utils/ACache.kt
@@ -525,7 +525,7 @@ class ACache private constructor(cacheDir: File, max_size: Long, max_count: Int)
         }
 
         fun hasDateInfo(data: ByteArray?): Boolean {
-            return (data != null && data.size > 15 && data[13] == '-'.toByte()
+            return (data != null && data.size > 15 && data[13] == '-'.code.toByte()
                     && indexOf(data, mSeparator) > 14)
         }
 
@@ -546,7 +546,7 @@ class ACache private constructor(cacheDir: File, max_size: Long, max_count: Int)
         @Suppress("SameParameterValue")
         private fun indexOf(data: ByteArray, c: Char): Int {
             for (i in data.indices) {
-                if (data[i] == c.toByte()) {
+                if (data[i] == c.code.toByte()) {
                     return i
                 }
             }
diff --git a/app/src/main/java/io/legado/app/utils/EncoderUtils.kt b/app/src/main/java/io/legado/app/utils/EncoderUtils.kt
index 976f1c1be..aafdb0d98 100644
--- a/app/src/main/java/io/legado/app/utils/EncoderUtils.kt
+++ b/app/src/main/java/io/legado/app/utils/EncoderUtils.kt
@@ -12,7 +12,7 @@ object EncoderUtils {
     fun escape(src: String): String {
         val tmp = StringBuilder()
         for (char in src) {
-            val charCode = char.toInt()
+            val charCode = char.code
             if (charCode in 48..57 || charCode in 65..90 || charCode in 97..122) {
                 tmp.append(char)
                 continue
diff --git a/app/src/main/java/io/legado/app/utils/EncodingDetect.kt b/app/src/main/java/io/legado/app/utils/EncodingDetect.kt
index 22f6c79d4..de698c8e0 100644
--- a/app/src/main/java/io/legado/app/utils/EncodingDetect.kt
+++ b/app/src/main/java/io/legado/app/utils/EncodingDetect.kt
@@ -26,14 +26,14 @@ object EncodingDetect {
                 }
                 val content = metaTag.attr("content")
                 val httpEquiv = metaTag.attr("http-equiv")
-                if (httpEquiv.toLowerCase(Locale.getDefault()) == "content-type") {
-                    charsetStr = if (content.toLowerCase(Locale.getDefault()).contains("charset")) {
+                if (httpEquiv.lowercase(Locale.getDefault()) == "content-type") {
+                    charsetStr = if (content.lowercase(Locale.getDefault()).contains("charset")) {
                         content.substring(
-                            content.toLowerCase(Locale.getDefault())
+                            content.lowercase(Locale.getDefault())
                                 .indexOf("charset") + "charset=".length
                         )
                     } else {
-                        content.substring(content.toLowerCase(Locale.getDefault()).indexOf(";") + 1)
+                        content.substring(content.lowercase(Locale.getDefault()).indexOf(";") + 1)
                     }
                     if (!TextUtils.isEmpty(charsetStr)) {
                         return charsetStr
diff --git a/app/src/main/java/io/legado/app/utils/NetworkUtils.kt b/app/src/main/java/io/legado/app/utils/NetworkUtils.kt
index 87be05e05..4bc22d456 100644
--- a/app/src/main/java/io/legado/app/utils/NetworkUtils.kt
+++ b/app/src/main/java/io/legado/app/utils/NetworkUtils.kt
@@ -12,17 +12,17 @@ object NetworkUtils {
 
     private val notNeedEncoding: BitSet by lazy {
         val bitSet = BitSet(256)
-        for (i in 'a'.toInt()..'z'.toInt()) {
+        for (i in 'a'.code..'z'.code) {
             bitSet.set(i)
         }
-        for (i in 'A'.toInt()..'Z'.toInt()) {
+        for (i in 'A'.code..'Z'.code) {
             bitSet.set(i)
         }
-        for (i in '0'.toInt()..'9'.toInt()) {
+        for (i in '0'.code..'9'.code) {
             bitSet.set(i)
         }
         for (char in "+-_.$:()!*@&#,[]") {
-            bitSet.set(char.toInt())
+            bitSet.set(char.code)
         }
         return@lazy bitSet
     }
@@ -38,7 +38,7 @@ object NetworkUtils {
         var i = 0
         while (i < str.length) {
             val c = str[i]
-            if (notNeedEncoding.get(c.toInt())) {
+            if (notNeedEncoding.get(c.code)) {
                 i++
                 continue
             }
diff --git a/app/src/main/java/io/legado/app/utils/StringUtils.kt b/app/src/main/java/io/legado/app/utils/StringUtils.kt
index feb428337..3a2bda745 100644
--- a/app/src/main/java/io/legado/app/utils/StringUtils.kt
+++ b/app/src/main/java/io/legado/app/utils/StringUtils.kt
@@ -114,7 +114,7 @@ object StringUtils {
 
     @SuppressLint("DefaultLocale")
     fun toFirstCapital(str: String): String {
-        return str.substring(0, 1).toUpperCase() + str.substring(1)
+        return str.substring(0, 1).uppercase(Locale.getDefault()) + str.substring(1)
     }
 
     /**
@@ -123,7 +123,7 @@ object StringUtils {
     fun halfToFull(input: String): String {
         val c = input.toCharArray()
         for (i in c.indices) {
-            if (c[i].toInt() == 32)
+            if (c[i].code == 32)
             //半角空格
             {
                 c[i] = 12288.toChar()
@@ -133,9 +133,9 @@ object StringUtils {
             //if (c[i] == 46) //半角点号，不转换
             // continue;
 
-            if (c[i].toInt() in 33..126)
+            if (c[i].code in 33..126)
             //其他符号都转换为全角
-                c[i] = (c[i].toInt() + 65248).toChar()
+                c[i] = (c[i].code + 65248).toChar()
         }
         return String(c)
     }
@@ -144,15 +144,15 @@ object StringUtils {
     fun fullToHalf(input: String): String {
         val c = input.toCharArray()
         for (i in c.indices) {
-            if (c[i].toInt() == 12288)
+            if (c[i].code == 12288)
             //全角空格
             {
                 c[i] = 32.toChar()
                 continue
             }
 
-            if (c[i].toInt() in 65281..65374)
-                c[i] = (c[i].toInt() - 65248).toChar()
+            if (c[i].code in 65281..65374)
+                c[i] = (c[i].code - 65248).toChar()
         }
         return String(c)
     }
@@ -255,10 +255,10 @@ object StringUtils {
         var start = 0
         val len = s.length
         var end = len - 1
-        while (start < end && (s[start].toInt() <= 0x20 || s[start] == '　')) {
+        while (start < end && (s[start].code <= 0x20 || s[start] == '　')) {
             ++start
         }
-        while (start < end && (s[end].toInt() <= 0x20 || s[end] == '　')) {
+        while (start < end && (s[end].code <= 0x20 || s[end] == '　')) {
             --end
         }
         if (end < len) ++end
diff --git a/build.gradle b/build.gradle
index 7305a5fc4..f826dc95c 100644
--- a/build.gradle
+++ b/build.gradle
@@ -4,7 +4,7 @@ buildscript {
     ext.kotlin_version = '1.5.0'
     repositories {
         google()
-        maven { url "https://maven.aliyun.com/nexus/content/groups/public/" }
+        maven { url 'https://maven.aliyun.com/repository/public/'}
         maven { url "https://s3.amazonaws.com/fabric-artifacts/public" }
         maven { url "https://maven.aliyun.com/repository/gradle-plugin" }
         maven { url "https://plugins.gradle.org/m2/" }
@@ -19,10 +19,9 @@ buildscript {
 allprojects {
     repositories {
         google()
-        maven { url "https://maven.aliyun.com/nexus/content/groups/public/" }
+        maven { url 'https://maven.aliyun.com/repository/public/'}
         maven { url "https://jitpack.io" }
         maven { url "https://maven.google.com/" }
-        //maven { url "https://github.com/psiegman/mvn-repo/raw/master/releases" }
     }
 }
 
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index ef1aa2fdc..f96ca89e9 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,6 +1,6 @@
-#Tue Oct 13 11:35:54 CST 2020
+#Fri May 07 15:24:46 CST 2021
 distributionBase=GRADLE_USER_HOME
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.8.3-bin.zip
 distributionPath=wrapper/dists
-zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.7.1-all.zip
+zipStoreBase=GRADLE_USER_HOME