Add navigation interface to make slide navigation consistent between …

…IntroActivity and SlideFragment (fix #155, fix #156, fix #166), fix #162

library/src/main/java/com/heinrichreimersoftware/materialintro/app/IntroActivity.java

@@ -68,7 +68,7 @@
 import java.util.List;
 
 @SuppressLint("Registered")
-public class IntroActivity extends AppCompatActivity {
+public class IntroActivity extends AppCompatActivity implements IntroNavigation {
     private static final String KEY_CURRENT_ITEM =
             "com.heinrichreimersoftware.materialintro.app.IntroActivity.KEY_CURRENT_ITEM";
     private static final String KEY_FULLSCREEN =
@@ -366,60 +366,102 @@ private long calculateScrollDuration(int distance) {
         return Math.round(pageScrollDuration * (distance + Math.sqrt(distance)) / 2);
     }
 
-    public void nextSlide() {
-        int currentItem = pager.getCurrentItem();
-        if (currentItem > adapter.getCount() - 1) finishIfNeeded();
+    @Override
+    public boolean goToSlide(int position) {
+        int lastPosition = pager.getCurrentItem();
 
-        if (canGoForward(currentItem, true)) {
-            smoothScrollPagerTo(++currentItem);
+        if (lastPosition >= adapter.getCount()) {
+            finishIfNeeded();
+        }
+
+        int newPosition = lastPosition;
+
+        position = Math.max(0, Math.min(position, getCount()));
+
+        if (position > lastPosition) {
+            // Go forward
+            while (newPosition < position && canGoForward(newPosition, true)) {
+                newPosition++;
+            }
+        } else if (position < lastPosition) {
+            // Go backward
+            while (newPosition > position && canGoBackward(newPosition, true)) {
+                newPosition--;
+            }
         }
         else {
-            AnimUtils.applyShakeAnimation(this, buttonNext);
+            // Noting to do here
+            return true;
         }
+
+        boolean blocked = false;
+        if (newPosition != position) {
+            // Could not go the complete way to the given position.
+            blocked = true;
+
+            if (position > lastPosition) {
+                AnimUtils.applyShakeAnimation(this, buttonNext);
+            } else if (position < lastPosition) {
+                AnimUtils.applyShakeAnimation(this, buttonBack);
+            }
+        }
+
+        // Scroll to new position
+        smoothScrollPagerTo(newPosition);
+
+        return !blocked;
+    }
+
+    @Override
+    public boolean nextSlide() {
+        int currentItem = pager.getCurrentItem();
+        return goToSlide(currentItem + 1);
     }
 
     private int nextSlideAuto() {
-        int endPosition = pager.getCurrentItem();
+        int lastPosition = pager.getCurrentItem();
         int count = getCount();
 
         if (count == 1) {
             return 0;
         }
         else if (pager.getCurrentItem() >= count - 1) {
-            while (endPosition >= 0 && canGoBackward(endPosition, true)) {
-                endPosition--;
+            while (lastPosition >= 0 && canGoBackward(lastPosition, true)) {
+                lastPosition--;
             }
             if (autoplayCounter > 0)
                 autoplayCounter--;
-        }
-        else if (canGoForward(endPosition, true)) {
-            endPosition++;
+        } else if (canGoForward(lastPosition, true)) {
+            lastPosition++;
         }
 
-        int distance = Math.abs(endPosition - pager.getCurrentItem());
+        int distance = Math.abs(lastPosition - pager.getCurrentItem());
 
-        if (endPosition == pager.getCurrentItem())
+        if (lastPosition == pager.getCurrentItem())
             return 0;
 
-        smoothScrollPagerTo(endPosition);
+        smoothScrollPagerTo(lastPosition);
 
         if (autoplayCounter == 0)
             return 0;
         return distance;
 
     }
 
-    public void previousSlide() {
+    @Override
+    public boolean previousSlide() {
         int currentItem = pager.getCurrentItem();
-        if (currentItem <= 0) return;
+        return goToSlide(currentItem - 1);
+    }
 
-        if (canGoBackward(currentItem, true)) {
-            smoothScrollPagerTo(--currentItem);
-        }
-        else {
-            AnimUtils.applyShakeAnimation(this, buttonBack);
+    @Override
+    public boolean goToLastSlide() {
+        return goToSlide(getCount() - 1);
+    }
 
-        }
+    @Override
+    public boolean goToFirstSlide() {
+        return goToSlide(0);
     }
 
     private void performButtonBackPress() {
@@ -436,8 +478,12 @@ private void performButtonBackPress() {
     }
 
     private boolean canGoForward(int position, boolean notifyListeners) {
-        if (position >= getCount())
+        if (position >= getCount()) {
             return false;
+        }
+        if (position <= 0) {
+            return true;
+        }
 
         if (buttonNextFunction == BUTTON_NEXT_FUNCTION_NEXT && position >= getCount() - 1)
             //Block finishing when button "next" function is not "finish".
@@ -454,8 +500,12 @@ private boolean canGoForward(int position, boolean notifyListeners) {
     }
 
     private boolean canGoBackward(int position, boolean notifyListeners) {
-        if (position <= 0)
+        if (position <= 0) {
             return false;
+        }
+        if (position >= getCount()) {
+            return true;
+        }
 
         boolean canGoBackward = (navigationPolicy == null || navigationPolicy.canGoBackward(position)) &&
                 getSlide(position).canGoBackward();

library/src/main/java/com/heinrichreimersoftware/materialintro/app/IntroNavigation.java

@@ -0,0 +1,47 @@
+package com.heinrichreimersoftware.materialintro.app;
+
+interface IntroNavigation {
+    /**
+     * Tries to go to the given position and will stop when {@code canGoForward()} or
+     * {@code canGoBackward()} returns {@code false}.
+     *
+     * @param position The position the pager should go to.
+     * @return {@code true} if the pager was able to go the complete way to the given position,
+     * {@code false} otherwise.
+     */
+    boolean goToSlide(int position);
+
+    /**
+     * Tries to go to the next slide if {@code canGoForward()} returns {@code true}.
+     *
+     * @return {@code true} if the pager was able to go to the next slide, {@code false} otherwise.
+     */
+    boolean nextSlide();
+
+
+    /**
+     * Tries to go to the previous slide if {@code canGoForward()} returns {@code true}.
+     *
+     * @return {@code true} if the pager was able to go to the previous slide, {@code false}
+     * otherwise.
+     */
+    boolean previousSlide();
+
+    /**
+     * Tries to go to the last slide and will stop when {@code canGoForward()} returns
+     * {@code false}.
+     *
+     * @return {@code true} if the pager was able to go the complete way to the last slide,
+     * {@code false} otherwise.
+     */
+    boolean goToLastSlide();
+
+    /**
+     * Tries to go to the first slide and will stop when {@code canGoBackward()} returns
+     * {@code false}.
+     *
+     * @return {@code true} if the pager was able to go the complete way to the first slide,
+     * {@code false} otherwise.
+     */
+    boolean goToFirstSlide();
+}

library/src/main/java/com/heinrichreimersoftware/materialintro/app/SlideFragment.java

@@ -3,7 +3,7 @@
 import android.support.v4.app.Fragment;
 import android.view.View;
 
-public class SlideFragment extends Fragment {
+public class SlideFragment extends Fragment implements IntroNavigation {
 
     public boolean canGoForward() {
         return true;
@@ -33,12 +33,29 @@ public void removeOnNavigationBlockedListener(OnNavigationBlockedListener listen
         getIntroActivity().removeOnNavigationBlockedListener(listener);
     }
 
-    protected void nextSlide() {
-        getIntroActivity().nextSlide();
+    @Override
+    public boolean goToSlide(int position) {
+        return getIntroActivity().goToSlide(position);
     }
 
-    protected void previousSlide() {
-        getIntroActivity().previousSlide();
+    @Override
+    public boolean nextSlide() {
+        return getIntroActivity().nextSlide();
+    }
+
+    @Override
+    public boolean previousSlide() {
+        return getIntroActivity().previousSlide();
+    }
+
+    @Override
+    public boolean goToLastSlide() {
+        return getIntroActivity().goToLastSlide();
+    }
+
+    @Override
+    public boolean goToFirstSlide() {
+        return getIntroActivity().goToFirstSlide();
     }
 
     /**

library/src/main/java/com/heinrichreimersoftware/materialintro/slide/SlideAdapter.java

@@ -125,8 +125,9 @@ public Object instantiateItem(ViewGroup container, int position) {
             //Load old fragment from fragment manager
             ((RestorableSlide) slide).setFragment(instantiatedFragment);
             data.set(position, slide);
-            if (instantiatedFragment instanceof SlideFragment)
+            if (instantiatedFragment instanceof SlideFragment && instantiatedFragment.isAdded()) {
                 ((SlideFragment) instantiatedFragment).updateNavigation();
+            }
         }
         return instantiatedFragment;
     }