Add scrollTo convenience methods

app/build.gradle

@@ -15,7 +15,8 @@ android {
 dependencies {
     implementation project(':gravitysnaphelper')
     implementation 'com.google.android.material:material:1.1.0-alpha01'
-    implementation 'androidx.appcompat:appcompat:1.0.0'
+    implementation 'androidx.appcompat:appcompat:1.0.2'
     implementation 'androidx.recyclerview:recyclerview:1.0.0'
     implementation 'androidx.cardview:cardview:1.0.0'
+    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
 }

app/src/main/java/com/github/rubensousa/recyclerviewsnap/SnapAdapter.java

@@ -10,6 +10,7 @@
 
 import com.github.rubensousa.gravitysnaphelper.GravityPagerSnapHelper;
 import com.github.rubensousa.gravitysnaphelper.GravitySnapHelper;
+import com.google.android.material.button.MaterialButton;
 
 import java.util.ArrayList;
 
@@ -22,19 +23,19 @@ public class SnapAdapter extends RecyclerView.Adapter<SnapAdapter.ViewHolder> im
     public static final int VERTICAL = 0;
     public static final int HORIZONTAL = 1;
 
-    private ArrayList<Snap> mSnaps;
+    private ArrayList<Snap> snaps;
 
     public SnapAdapter() {
-        mSnaps = new ArrayList<>();
+        snaps = new ArrayList<>();
     }
 
     public void addSnap(Snap snap) {
-        mSnaps.add(snap);
+        snaps.add(snap);
     }
 
     @Override
     public int getItemViewType(int position) {
-        Snap snap = mSnaps.get(position);
+        Snap snap = snaps.get(position);
         switch (snap.getGravity()) {
             case Gravity.CENTER_VERTICAL:
                 return VERTICAL;
@@ -64,8 +65,8 @@ public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
 
     @Override
     public void onBindViewHolder(ViewHolder holder, int position) {
-        Snap snap = mSnaps.get(position);
-        holder.snapTextView.setText(snap.getText());
+        holder.bind(snaps.get(position));
+        Snap snap = snaps.get(position);
         int padding = holder.recyclerView.getResources().getDimensionPixelOffset(R.dimen.extra_padding);
         if (snap.getPadding()) {
             if (snap.getGravity() == Gravity.START) {
@@ -106,25 +107,56 @@ public void onBindViewHolder(ViewHolder holder, int position) {
 
     @Override
     public int getItemCount() {
-        return mSnaps.size();
+        return snaps.size();
     }
 
     @Override
     public void onSnap(int position) {
         Log.d("Snapped: ", position + "");
     }
 
-    public static class ViewHolder extends RecyclerView.ViewHolder {
+    public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
 
         public TextView snapTextView;
         public RecyclerView recyclerView;
+        public MaterialButton scrollButton;
+        private Snap snap;
 
         public ViewHolder(View itemView) {
             super(itemView);
             snapTextView = itemView.findViewById(R.id.snapTextView);
             recyclerView = itemView.findViewById(R.id.recyclerView);
+            scrollButton = itemView.findViewById(R.id.scrollButton);
+            scrollButton.setOnClickListener(this);
         }
 
+        public void bind(Snap snap) {
+            this.snap = snap;
+            if ((snap.getGravity() == Gravity.START || snap.getGravity() == Gravity.END)
+                    && !snap.getPadding()) {
+                scrollButton.setVisibility(View.VISIBLE);
+            } else {
+                scrollButton.setVisibility(View.INVISIBLE);
+            }
+            snapTextView.setText(snap.getText());
+        }
+
+        @Override
+        public void onClick(View v) {
+            RecyclerView.OnFlingListener listener = recyclerView.getOnFlingListener();
+            RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
+            if (listener instanceof GravitySnapHelper
+                    && layoutManager instanceof LinearLayoutManager) {
+                LinearLayoutManager lm = (LinearLayoutManager) layoutManager;
+                int firstVisiblePosition = snap.getGravity() == Gravity.START ?
+                        lm.findFirstCompletelyVisibleItemPosition()
+                        : lm.findLastCompletelyVisibleItemPosition();
+                if (firstVisiblePosition != RecyclerView.NO_POSITION) {
+                    ((GravitySnapHelper) listener).smoothScrollToPosition(
+                            firstVisiblePosition + 1);
+                }
+            }
+        }
     }
 }
 

app/src/main/res/layout/adapter_snap.xml

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
-<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
-    android:layout_height="wrap_content"
-    android:orientation="vertical">
+    android:layout_height="wrap_content">
 
     <TextView
         android:id="@+id/snapTextView"
@@ -14,13 +14,33 @@
         android:layout_marginEnd="@dimen/activity_horizontal_margin"
         android:layout_marginRight="@dimen/activity_horizontal_margin"
         android:text="Snap center"
-        android:textAppearance="@style/TextAppearance.AppCompat.Title" />
+        android:textAppearance="@style/TextAppearance.AppCompat.Title"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
+
+    <com.google.android.material.button.MaterialButton
+        android:id="@+id/scrollButton"
+        style="@style/Widget.MaterialComponents.Button.TextButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginEnd="@dimen/activity_horizontal_margin"
+        android:layout_marginRight="@dimen/activity_horizontal_margin"
+        android:text="Scroll +1"
+        android:textAppearance="@style/TextAppearance.AppCompat.Title"
+        app:layout_constraintBottom_toBottomOf="@id/snapTextView"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintTop_toTopOf="@id/snapTextView" />
+
 
     <com.github.rubensousa.gravitysnaphelper.OrientationAwareRecyclerView
         android:id="@+id/recyclerView"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_marginTop="8dp"
         android:clipToPadding="false"
-        android:padding="4dp" />
-</LinearLayout>
+        android:padding="4dp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/scrollButton" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/values/styles.xml

@@ -1,7 +1,7 @@
 <resources>
 
     <!-- Base application theme. -->
-    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
+    <style name="AppTheme" parent="Theme.MaterialComponents.Light.NoActionBar">
         <!-- Customize your theme here. -->
         <item name="colorPrimary">@color/colorPrimary</item>
         <item name="colorPrimaryDark">@color/colorPrimaryDark</item>

gravitysnaphelper/src/main/java/com/github/rubensousa/gravitysnaphelper/GravityDelegate.java

@@ -80,6 +80,36 @@ public void attachToRecyclerView(@Nullable RecyclerView recyclerView) {
         }
     }
 
+    public void smoothScrollToPosition(int position) {
+        scrollTo(position, true);
+    }
+
+    public void scrollToPosition(int position) {
+        scrollTo(position, false);
+    }
+
+    private void scrollTo(int position, boolean smooth) {
+        if (recyclerView.getLayoutManager() != null) {
+            RecyclerView.ViewHolder viewHolder
+                    = recyclerView.findViewHolderForAdapterPosition(position);
+            if (viewHolder != null) {
+                int[] distances = calculateDistanceToFinalSnap(recyclerView.getLayoutManager(),
+                        viewHolder.itemView);
+                if (smooth) {
+                    recyclerView.smoothScrollBy(distances[0], distances[1]);
+                } else {
+                    recyclerView.scrollBy(distances[0], distances[1]);
+                }
+            } else {
+                if (smooth) {
+                    recyclerView.smoothScrollToPosition(position);
+                } else {
+                    recyclerView.scrollToPosition(position);
+                }
+            }
+        }
+    }
+
     @NonNull
     public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager,
                                               @NonNull View targetView) {

gravitysnaphelper/src/main/java/com/github/rubensousa/gravitysnaphelper/GravityPagerSnapHelper.java

@@ -80,4 +80,13 @@ public View findSnapView(RecyclerView.LayoutManager layoutManager) {
     public void enableLastItemSnap(boolean snap) {
         delegate.enableLastItemSnap(snap);
     }
+
+    public void smoothScrollToPosition(int position) {
+        delegate.smoothScrollToPosition(position);
+    }
+
+    public void scrollToPosition(int position) {
+        delegate.scrollToPosition(position);
+    }
+
 }

gravitysnaphelper/src/main/java/com/github/rubensousa/gravitysnaphelper/GravitySnapHelper.java

@@ -16,16 +16,18 @@
 
 package com.github.rubensousa.gravitysnaphelper;
 
+import android.view.View;
+
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.recyclerview.widget.LinearSnapHelper;
 import androidx.recyclerview.widget.RecyclerView;
-import android.view.View;
 
 
 public class GravitySnapHelper extends LinearSnapHelper {
 
-    @NonNull private final GravityDelegate delegate;
+    @NonNull
+    private final GravityDelegate delegate;
 
     public GravitySnapHelper(int gravity) {
         this(gravity, false, null);
@@ -69,6 +71,14 @@ public void enableLastItemSnap(boolean snap) {
         delegate.enableLastItemSnap(snap);
     }
 
+    public void smoothScrollToPosition(int position) {
+        delegate.smoothScrollToPosition(position);
+    }
+
+    public void scrollToPosition(int position) {
+        delegate.scrollToPosition(position);
+    }
+
     public interface SnapListener {
         void onSnap(int position);
     }