feat: 优化代码

app/src/main/java/io/legado/app/ui/download/DownloadViewModel.kt

@@ -36,13 +36,13 @@ class DownloadViewModel(application: Application) : BaseViewModel(application) {
     }
 
     private fun export(doc: DocumentFile, book: Book) {
-        DocumentUtils.createFileIfNotExist(doc, book.name)
+        DocumentUtils.createFileIfNotExist(doc, "${book.name}.txt")
-            ?.uri
             ?.writeText(context, getAllContents(book))
     }
 
     private fun export(file: File, book: Book) {
-        FileUtils.createFileIfNotExist(file, book.name).writeText(getAllContents(book))
+        FileUtils.createFileIfNotExist(file, "${book.name}.txt")
+            .writeText(getAllContents(book))
     }
 
     private fun getAllContents(book: Book): String {

app/src/main/java/io/legado/app/utils/DocumentUtils.kt

@@ -7,7 +7,7 @@ import android.provider.DocumentsContract
 import androidx.documentfile.provider.DocumentFile
 import java.util.*
 
-@Suppress("unused")
+
 object DocumentUtils {
 
     fun exists(root: DocumentFile, fileName: String, vararg subDirs: String): Boolean {
@@ -139,3 +139,23 @@ data class DocItem(
         DocumentsContract.Document.MIME_TYPE_DIR == attr
     }
 }
+
+@Throws(Exception::class)
+fun DocumentFile.writeText(context: Context, data: String) {
+    DocumentUtils.writeText(context, data, this.uri)
+}
+
+@Throws(Exception::class)
+fun DocumentFile.writeBytes(context: Context, data: ByteArray) {
+    DocumentUtils.writeBytes(context, data, this.uri)
+}
+
+@Throws(Exception::class)
+fun DocumentFile.readText(context: Context): String? {
+    return DocumentUtils.readText(context, this.uri)
+}
+
+@Throws(Exception::class)
+fun DocumentFile.readBytes(context: Context): ByteArray? {
+    return DocumentUtils.readBytes(context, this.uri)
+}