diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index 8a91a6b..4d33b6c 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https://services.gradle.org/distributions/gradle-6.5.1-all.zip
+distributionUrl=https://home/d/services.gradle.org/distributions/gradle-6.5.1-all.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
diff --git a/src/main/java/com/reandroid/lib/arsc/chunk/PackageBlock.java b/src/main/java/com/reandroid/lib/arsc/chunk/PackageBlock.java
index deda5d1..c31b529 100644
--- a/src/main/java/com/reandroid/lib/arsc/chunk/PackageBlock.java
+++ b/src/main/java/com/reandroid/lib/arsc/chunk/PackageBlock.java
@@ -189,7 +189,6 @@ public class PackageBlock extends BaseChunk {
             return;
         }
         updateEntryGroup(entryBlock);
-        updateEntrySpecReference(entryBlock);
         updateEntryTableReferences(entryBlock);
     }
     private void updateEntryTableReferences(EntryBlock entryBlock){
@@ -201,11 +200,6 @@ public class PackageBlock extends BaseChunk {
         TableStringPool tableStringPool=tableBlock.getTableStringPool();
         tableStringPool.addReferences(tableReferences);
     }
-    private void updateEntrySpecReference(EntryBlock entryBlock){
-        ReferenceItem specRef=entryBlock.getSpecReferenceBlock();
-        SpecStringPool specStringPool=getSpecStringPool();
-        specStringPool.addReference(specRef);
-    }
     private void updateEntryGroup(EntryBlock entryBlock){
         int resId=entryBlock.getResourceId();
         EntryGroup group=mEntriesGroup.get(resId);
diff --git a/src/main/java/com/reandroid/lib/arsc/group/EntryGroup.java b/src/main/java/com/reandroid/lib/arsc/group/EntryGroup.java
index b05d633..ca6b216 100644
--- a/src/main/java/com/reandroid/lib/arsc/group/EntryGroup.java
+++ b/src/main/java/com/reandroid/lib/arsc/group/EntryGroup.java
@@ -8,6 +8,8 @@ import com.reandroid.lib.arsc.item.TypeString;
 import com.reandroid.lib.arsc.pool.SpecStringPool;
 import com.reandroid.lib.arsc.value.EntryBlock;
 
+import java.util.Iterator;
+
 public class EntryGroup extends ItemGroup<EntryBlock> {
     private final int resourceId;
     public EntryGroup(int resId) {
@@ -17,43 +19,55 @@ public class EntryGroup extends ItemGroup<EntryBlock> {
     public int getResourceId(){
         return resourceId;
     }
-    public void renameSpec(String name){
+    public boolean renameSpec(String name){
         EntryBlock[] items=getItems();
-        if(items==null){
-            return;
+        if(items==null || name==null){
+            return false;
         }
         SpecStringPool specStringPool=getSpecStringPool();
         if(specStringPool==null){
-            return;
+            return false;
+        }
+        String oldName=getSpecName();
+        if(name.equals(oldName)){
+            return false;
         }
         SpecString specString=specStringPool.getOrCreate(name);
-        renameSpec(specString.getIndex());
+        return renameSpec(specString.getIndex());
     }
-    public void renameSpec(int specReference){
+    public boolean renameSpec(int specReference){
         EntryBlock[] items=getItems();
         if(items==null){
-            return;
+            return false;
         }
+        boolean renameOk=false;
         for(EntryBlock block:items){
             if(block==null||block.isNull()){
                 continue;
             }
+            if(block.getSpecReference()==specReference){
+                continue;
+            }
             block.setSpecReference(specReference);
+            renameOk=true;
         }
+        return renameOk;
     }
     public TypeString getTypeString(){
-        EntryBlock entryBlock=get(0);
-        if(entryBlock==null){
-            return null;
+        Iterator<EntryBlock> itr=iterator(true);
+        while (itr.hasNext()){
+            EntryBlock entryBlock=itr.next();
+            return entryBlock.getTypeString();
         }
-        return entryBlock.getTypeString();
+        return null;
     }
     public SpecString getSpecString(){
-        EntryBlock entryBlock=get(0);
-        if(entryBlock==null){
-            return null;
+        Iterator<EntryBlock> itr=iterator(true);
+        while (itr.hasNext()){
+            EntryBlock entryBlock=itr.next();
+            return entryBlock.getSpecString();
         }
-        return entryBlock.getSpecString();
+        return null;
     }
     public String getTypeName(){
         TypeString typeString=getTypeString();
diff --git a/src/main/java/com/reandroid/lib/arsc/group/ItemGroup.java b/src/main/java/com/reandroid/lib/arsc/group/ItemGroup.java
index bd84d56..7bddff5 100644
--- a/src/main/java/com/reandroid/lib/arsc/group/ItemGroup.java
+++ b/src/main/java/com/reandroid/lib/arsc/group/ItemGroup.java
@@ -4,6 +4,7 @@ import com.reandroid.lib.arsc.base.Block;
 import com.reandroid.lib.arsc.base.BlockArrayCreator;
 
 import java.util.AbstractList;
+import java.util.Iterator;
 import java.util.List;
 
 public class ItemGroup<T extends Block> {
@@ -17,6 +18,12 @@ public class ItemGroup<T extends Block> {
         this.items=blockArrayCreator.newInstance(0);
         this.hashCode=(getClass().getName()+"-"+name).hashCode();
     }
+    public Iterator<T> iterator(){
+        return iterator(false);
+    }
+    public Iterator<T> iterator(boolean skipNullBlock){
+        return new GroupIterator(skipNullBlock);
+    }
     public List<T> listItems(){
         return new AbstractList<T>() {
             @Override
@@ -128,4 +135,47 @@ public class ItemGroup<T extends Block> {
     public String toString(){
         return items.length+"{"+name+"}";
     }
+
+
+    private class GroupIterator implements Iterator<T> {
+        private int mCursor;
+        private int mMaxSize;
+        private final boolean mSkipNullBlock;
+        GroupIterator(boolean skipNullBlock){
+            mSkipNullBlock=skipNullBlock;
+            mCursor=0;
+            mMaxSize=ItemGroup.this.size();
+        }
+        @Override
+        public boolean hasNext() {
+            checkCursor();
+            return !isFinished();
+        }
+        @Override
+        public T next() {
+            if(!isFinished()){
+                T item=ItemGroup.this.get(mCursor);
+                mCursor++;
+                checkCursor();
+                return item;
+            }
+            return null;
+        }
+        private boolean isFinished(){
+            return mCursor>=mMaxSize;
+        }
+        private void checkCursor(){
+            if(!mSkipNullBlock || isFinished()){
+                return;
+            }
+            T item=ItemGroup.this.get(mCursor);
+            while (item==null||item.isNull()){
+                mCursor++;
+                item=ItemGroup.this.get(mCursor);
+                if(mCursor>=mMaxSize){
+                    break;
+                }
+            }
+        }
+    }
 }
diff --git a/src/main/java/com/reandroid/lib/arsc/item/StringItem.java b/src/main/java/com/reandroid/lib/arsc/item/StringItem.java
index 38c40ac..d92ff65 100644
--- a/src/main/java/com/reandroid/lib/arsc/item/StringItem.java
+++ b/src/main/java/com/reandroid/lib/arsc/item/StringItem.java
@@ -24,8 +24,14 @@ public class StringItem extends BlockItem {
         this.mUtf8=utf8;
         this.mReferencedList=new ArrayList<>();
     }
-    public void removeReference(IntegerItem ref){
-        mReferencedList.remove(ref);
+    public boolean removeReference(ReferenceItem ref){
+        return mReferencedList.remove(ref);
+    }
+    public boolean removeAllReference(Collection<ReferenceItem> referenceItems){
+        return mReferencedList.removeAll(referenceItems);
+    }
+    public void removeAllReference(){
+        mReferencedList.clear();
     }
     public List<ReferenceItem> getReferencedList(){
         return mReferencedList;
diff --git a/src/main/java/com/reandroid/lib/arsc/item/TypeString.java b/src/main/java/com/reandroid/lib/arsc/item/TypeString.java
index 28b2605..98beaba 100644
--- a/src/main/java/com/reandroid/lib/arsc/item/TypeString.java
+++ b/src/main/java/com/reandroid/lib/arsc/item/TypeString.java
@@ -5,8 +5,8 @@ public class TypeString extends StringItem {
     public TypeString(boolean utf8) {
         super(utf8);
     }
-    public int getId(){
-        return getIndex()+1;
+    public byte getId(){
+        return (byte) (getIndex()+1);
     }
     @Override
     StyleItem getStyle(){
diff --git a/src/main/java/com/reandroid/lib/arsc/pool/BaseStringPool.java b/src/main/java/com/reandroid/lib/arsc/pool/BaseStringPool.java
index 8e30bec..0f1d73c 100644
--- a/src/main/java/com/reandroid/lib/arsc/pool/BaseStringPool.java
+++ b/src/main/java/com/reandroid/lib/arsc/pool/BaseStringPool.java
@@ -66,6 +66,16 @@ public abstract class BaseStringPool<T extends StringItem> extends BaseChunk imp
 
     }
 
+    public boolean removeReference(ReferenceItem ref){
+        if(ref==null){
+            return false;
+        }
+        T item=get(ref.get());
+        if(item!=null){
+            return item.removeReference(ref);
+        }
+        return false;
+    }
     public void addReference(ReferenceItem ref){
         if(ref==null){
             return;
diff --git a/src/main/java/com/reandroid/lib/arsc/value/BaseResValue.java b/src/main/java/com/reandroid/lib/arsc/value/BaseResValue.java
index 220eae0..8d7b236 100644
--- a/src/main/java/com/reandroid/lib/arsc/value/BaseResValue.java
+++ b/src/main/java/com/reandroid/lib/arsc/value/BaseResValue.java
@@ -1,9 +1,13 @@
 package com.reandroid.lib.arsc.value;
 
 import com.reandroid.lib.arsc.base.Block;
+import com.reandroid.lib.arsc.chunk.PackageBlock;
+import com.reandroid.lib.arsc.chunk.TableBlock;
 import com.reandroid.lib.arsc.item.BlockItem;
 import com.reandroid.lib.arsc.item.IntegerItem;
 import com.reandroid.lib.arsc.item.ReferenceItem;
+import com.reandroid.lib.arsc.pool.SpecStringPool;
+import com.reandroid.lib.arsc.pool.TableStringPool;
 
 import java.util.List;
 
@@ -24,6 +28,35 @@ public abstract class BaseResValue extends BlockItem  {
         return null;
     }
 
+    boolean removeSpecReference(ReferenceItem ref){
+        EntryBlock entryBlock=getEntryBlock();
+        if(entryBlock==null){
+            return false;
+        }
+        return entryBlock.removeSpecReference(ref);
+    }
+    boolean removeTableReference(ReferenceItem ref){
+        EntryBlock entryBlock=getEntryBlock();
+        if(entryBlock==null){
+            return false;
+        }
+        return entryBlock.removeTableReference(ref);
+    }
+    void addSpecReference(ReferenceItem ref){
+        EntryBlock entryBlock=getEntryBlock();
+        if(entryBlock==null){
+            return;
+        }
+        entryBlock.addSpecReference(ref);
+    }
+    void addTableReference(ReferenceItem ref){
+        EntryBlock entryBlock=getEntryBlock();
+        if(entryBlock==null){
+            return;
+        }
+        entryBlock.addTableReference(ref);
+    }
+
 
 
     @Override
diff --git a/src/main/java/com/reandroid/lib/arsc/value/BaseResValueItem.java b/src/main/java/com/reandroid/lib/arsc/value/BaseResValueItem.java
index 5d90ad6..6b53677 100644
--- a/src/main/java/com/reandroid/lib/arsc/value/BaseResValueItem.java
+++ b/src/main/java/com/reandroid/lib/arsc/value/BaseResValueItem.java
@@ -17,6 +17,18 @@ public abstract class BaseResValueItem extends BaseResValue implements ResValueI
         }
         return mReferenceItem;
     }
+    boolean removeTableReference(){
+        ReferenceItem ref=mReferenceItem;
+        if(ref==null){
+            return false;
+        }
+        EntryBlock entryBlock=getEntryBlock();
+        if(entryBlock==null){
+            return false;
+        }
+        mReferenceItem=null;
+        return entryBlock.removeTableReference(ref);
+    }
     private ReferenceItem createReferenceItem(){
         return new ReferenceItem() {
             @Override
diff --git a/src/main/java/com/reandroid/lib/arsc/value/EntryBlock.java b/src/main/java/com/reandroid/lib/arsc/value/EntryBlock.java
index b487dff..e4e16d5 100644
--- a/src/main/java/com/reandroid/lib/arsc/value/EntryBlock.java
+++ b/src/main/java/com/reandroid/lib/arsc/value/EntryBlock.java
@@ -3,10 +3,12 @@ package com.reandroid.lib.arsc.value;
 import com.reandroid.lib.arsc.base.Block;
 import com.reandroid.lib.arsc.base.BlockCounter;
 import com.reandroid.lib.arsc.chunk.PackageBlock;
+import com.reandroid.lib.arsc.chunk.TableBlock;
 import com.reandroid.lib.arsc.chunk.TypeBlock;
 import com.reandroid.lib.arsc.io.BlockReader;
 import com.reandroid.lib.arsc.item.*;
 import com.reandroid.lib.arsc.pool.SpecStringPool;
+import com.reandroid.lib.arsc.pool.TableStringPool;
 
 
 import java.io.IOException;
@@ -43,6 +45,59 @@ public class EntryBlock extends Block {
         }
         return results;
     }
+    boolean removeSpecReference(ReferenceItem ref){
+        if(ref==null){
+            return false;
+        }
+        PackageBlock packageBlock=getPackageBlock();
+        if(packageBlock==null){
+            return false;
+        }
+        SpecStringPool specStringPool=packageBlock.getSpecStringPool();
+        return specStringPool.removeReference(ref);
+    }
+    boolean removeTableReference(ReferenceItem ref){
+        if(ref==null){
+            return false;
+        }
+        PackageBlock packageBlock=getPackageBlock();
+        if(packageBlock==null){
+            return false;
+        }
+        TableBlock tableBlock=packageBlock.getTableBlock();
+        if(tableBlock==null){
+            return false;
+        }
+        TableStringPool tableStringPool=tableBlock.getTableStringPool();
+        return tableStringPool.removeReference(ref);
+    }
+
+    void addSpecReference(ReferenceItem ref){
+        if(ref==null){
+            return;
+        }
+        PackageBlock packageBlock=getPackageBlock();
+        if(packageBlock==null){
+            return;
+        }
+        SpecStringPool specStringPool=packageBlock.getSpecStringPool();
+        specStringPool.addReference(ref);
+    }
+    void addTableReference(ReferenceItem ref){
+        if(ref==null){
+            return;
+        }
+        PackageBlock packageBlock=getPackageBlock();
+        if(packageBlock==null){
+            return;
+        }
+        TableBlock tableBlock=packageBlock.getTableBlock();
+        if(tableBlock==null){
+            return;
+        }
+        TableStringPool tableStringPool=tableBlock.getTableStringPool();
+        tableStringPool.addReference(ref);
+    }
 
     public short getFlags(){
         return mFlags.get();
@@ -57,7 +112,12 @@ public class EntryBlock extends Block {
         return mSpecReference.get();
     }
     public void setSpecReference(int ref){
+        int old=mSpecReference.get();
+        if(ref==old){
+            return;
+        }
         mSpecReference.set(ref);
+        updateSpecRef(old, ref);
     }
     public BaseResValue getResValue(){
         return mResValue;
@@ -74,6 +134,7 @@ public class EntryBlock extends Block {
             boolean is_complex=(resValue instanceof ResValueBag);
             setFlagComplex(is_complex);
             updatePackage();
+            updateSpecRef();
         }
     }
     private void setResValueInternal(BaseResValue resValue){
@@ -111,11 +172,7 @@ public class EntryBlock extends Block {
         return null;
     }
     public SpecString getSpecString(){
-        TypeBlock typeBlock=getTypeBlock();
-        if(typeBlock==null){
-            return null;
-        }
-        PackageBlock packageBlock=typeBlock.getPackageBlock();
+        PackageBlock packageBlock=getPackageBlock();
         if(packageBlock==null){
             return null;
         }
@@ -173,6 +230,13 @@ public class EntryBlock extends Block {
         int entryId=getIndex();
         return ((pkgId << 24) | (typeId << 16) | entryId);
     }
+    public PackageBlock getPackageBlock(){
+        TypeBlock typeBlock=getTypeBlock();
+        if(typeBlock!=null){
+            return typeBlock.getPackageBlock();
+        }
+        return null;
+    }
     public TypeBlock getTypeBlock(){
         Block parent=getParent();
         while (parent!=null){
@@ -326,6 +390,28 @@ public class EntryBlock extends Block {
         return result;
     }
 
+    private void updateSpecRef(){
+        updateSpecRef(-1, getSpecReference());
+    }
+    private void updateSpecRef(int oldRef, int newNef){
+        TypeBlock typeBlock=getTypeBlock();
+        if(typeBlock==null){
+            return;
+        }
+        PackageBlock packageBlock=typeBlock.getPackageBlock();
+        if(packageBlock==null){
+            return;
+        }
+        SpecStringPool specStringPool=packageBlock.getSpecStringPool();
+        SpecString specString=specStringPool.get(oldRef);
+        if(specString!=null){
+            specString.removeReference(getSpecReferenceBlock());
+        }
+        SpecString specStringNew=specStringPool.get(newNef);
+        if(specStringNew!=null){
+            specStringNew.addReference(getSpecReferenceBlock());
+        }
+    }
     private void updatePackage(){
         TypeBlock typeBlock=getTypeBlock();
         if(typeBlock==null){
@@ -347,6 +433,7 @@ public class EntryBlock extends Block {
         createResValue();
         mResValue.readBytes(reader);
         updatePackage();
+        updateSpecRef();
     }
     public String toString(){
         StringBuilder builder=new StringBuilder();
diff --git a/src/main/java/com/reandroid/lib/arsc/value/ResValueBagItem.java b/src/main/java/com/reandroid/lib/arsc/value/ResValueBagItem.java
index 34ae508..9026d7b 100644
--- a/src/main/java/com/reandroid/lib/arsc/value/ResValueBagItem.java
+++ b/src/main/java/com/reandroid/lib/arsc/value/ResValueBagItem.java
@@ -1,5 +1,7 @@
 package com.reandroid.lib.arsc.value;
 
+import com.reandroid.lib.arsc.item.ReferenceItem;
+
 public class ResValueBagItem extends BaseResValueItem{
 
     public ResValueBagItem() {
@@ -41,7 +43,16 @@ public class ResValueBagItem extends BaseResValueItem{
     }
     @Override
     public void setType(byte type){
+        byte old=getType();
+        if(type==old){
+            return;
+        }
+        removeTableReference();
         setByte(OFFSET_TYPE, type);
+        if(type==ValueType.STRING.getByte()){
+            ReferenceItem ref=getTableStringReference();
+            removeTableReference(ref);
+        }
     }
     @Override
     public byte getType(){
@@ -53,7 +64,17 @@ public class ResValueBagItem extends BaseResValueItem{
     }
     @Override
     public void setData(int data){
+        int old=getData();
+        if(data==old){
+            return;
+        }
+        if(getValueType()==ValueType.STRING){
+            removeTableReference();
+        }
         setInt(OFFSET_DATA, data);
+        if(getValueType()==ValueType.STRING){
+            addTableReference(getTableStringReference());
+        }
     }
 
     @Override
diff --git a/src/main/java/com/reandroid/lib/arsc/value/ResValueInt.java b/src/main/java/com/reandroid/lib/arsc/value/ResValueInt.java
index 1784201..789b053 100644
--- a/src/main/java/com/reandroid/lib/arsc/value/ResValueInt.java
+++ b/src/main/java/com/reandroid/lib/arsc/value/ResValueInt.java
@@ -29,7 +29,15 @@ public class ResValueInt extends BaseResValueItem  {
     }
     @Override
     public void setType(byte type){
+        byte old=getType();
+        if(type==old){
+            return;
+        }
+        removeTableReference();
         setByte(OFFSET_TYPE, type);
+        if(type==ValueType.STRING.getByte()){
+            addTableReference(getTableStringReference());
+        }
     }
     @Override
     public byte getType(){
@@ -41,7 +49,15 @@ public class ResValueInt extends BaseResValueItem  {
     }
     @Override
     public void setData(int data){
+        int old=getData();
+        if(data==old){
+            return;
+        }
+        removeTableReference();
         setInt(OFFSET_DATA, data);
+        if(getValueType()==ValueType.STRING){
+            addTableReference(getTableStringReference());
+        }
     }