diff --git a/autojs/src/main/java/com/stardust/autojs/core/image/ImageWrapper.java b/autojs/src/main/java/com/stardust/autojs/core/image/ImageWrapper.java
index 5bc45854..113ae962 100644
--- a/autojs/src/main/java/com/stardust/autojs/core/image/ImageWrapper.java
+++ b/autojs/src/main/java/com/stardust/autojs/core/image/ImageWrapper.java
@@ -79,7 +79,7 @@ public class ImageWrapper {
     }
 
     public Mat getMat() {
-        if (mMat == null) {
+        if (mMat == null && mBitmap != null) {
             mMat = new Mat();
             Utils.bitmapToMat(mBitmap, mMat);
         }
@@ -87,6 +87,7 @@ public class ImageWrapper {
     }
 
     public void saveTo(String path) {
+        ensureNotRecycled();
         if (mBitmap != null) {
             try {
                 mBitmap.compress(Bitmap.CompressFormat.PNG, 100, new FileOutputStream(path));
@@ -99,6 +100,7 @@ public class ImageWrapper {
     }
 
     public int pixel(int x, int y) {
+        ensureNotRecycled();
         if (mBitmap != null) {
             return mBitmap.getPixel(x, y);
         }
@@ -121,4 +123,9 @@ public class ImageWrapper {
         }
 
     }
+
+    private void ensureNotRecycled() {
+        if (mBitmap == null && mMat == null)
+            throw new IllegalStateException("image has been recycled");
+    }
 }
diff --git a/automator/src/main/java/com/stardust/automator/UiGlobalSelector.java b/automator/src/main/java/com/stardust/automator/UiGlobalSelector.java
index e792acab..f05508ca 100644
--- a/automator/src/main/java/com/stardust/automator/UiGlobalSelector.java
+++ b/automator/src/main/java/com/stardust/automator/UiGlobalSelector.java
@@ -396,6 +396,11 @@ public class UiGlobalSelector {
         return this;
     }
 
+    public UiGlobalSelector indexInParent(int index) {
+        mFilters.add(new IntFilter(IntFilter.INDEX_IN_PARENT, index));
+        return this;
+    }
+
 
     public UiGlobalSelector filter(final BooleanFilter.BooleanSupplier filter) {
         mFilters.add(new DfsFilter() {
diff --git a/automator/src/main/java/com/stardust/automator/filter/IntFilter.java b/automator/src/main/java/com/stardust/automator/filter/IntFilter.java
index d5b356a7..18d59dd7 100644
--- a/automator/src/main/java/com/stardust/automator/filter/IntFilter.java
+++ b/automator/src/main/java/com/stardust/automator/filter/IntFilter.java
@@ -96,6 +96,18 @@ public class IntFilter extends DfsFilter {
         }
     };
 
+    public static final IntProperty INDEX_IN_PARENT = new IntProperty() {
+        @Override
+        public int get(UiObject object) {
+            return object.indexInParent();
+        }
+
+        @Override
+        public String toString() {
+            return "indexInParent";
+        }
+    };
+
     private IntProperty mIntProperty;
     private int mValue;