java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“boolean android.graphics.Bitmap.isRecycled()”

Question

I am trying to implement swipe to delete in RecyclerView. Everything seems to be working fine except drawing a delete icon below the item that's being swiped.

This is how I am doing it:

ItemTouchHelper.SimpleCallback simpleItemTouchCallback = new ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {

            @Override
            public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
                return false;
            }

            @Override
            public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
                int position = viewHolder.getAdapterPosition();

//                Do my stuff
//                }
            }

            @Override
            public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {

                Bitmap icon;
                if(actionState == ItemTouchHelper.ACTION_STATE_SWIPE){

                    View itemView = viewHolder.itemView;
                    float height = (float) itemView.getBottom() - (float) itemView.getTop();
                    float width = height / 3;

                    if(dX > 0){
                        p.setColor(Color.parseColor("#388E3C"));
                        RectF background = new RectF((float) itemView.getLeft(), (float) itemView.getTop(), dX,(float) itemView.getBottom());
                        c.drawRect(background,p);
                        icon = BitmapFactory.decodeResource(getActivity().getResources(), R.drawable.ic_delete);
                        RectF icon_dest = new RectF((float) itemView.getLeft() + width ,(float) itemView.getTop() + width,(float) itemView.getLeft()+ 2*width,(float)itemView.getBottom() - width);
                        c.drawBitmap(icon,null,icon_dest,p);
                    } else {
                        p.setColor(Color.parseColor("#D32F2F"));
                        RectF background = new RectF((float) itemView.getRight() + dX, (float) itemView.getTop(),(float) itemView.getRight(), (float) itemView.getBottom());
                        c.drawRect(background,p);
                        icon = BitmapFactory.decodeResource(getActivity().getResources(), R.drawable.ic_delete);
                        RectF icon_dest = new RectF((float) itemView.getRight() - 2*width ,(float) itemView.getTop() + width,(float) itemView.getRight() - width,(float)itemView.getBottom() - width);
                        c.drawBitmap(icon,null,icon_dest,p);
                    }
                }
                super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
            }
        };
        ItemTouchHelper itemTouchHelper = new ItemTouchHelper(simpleItemTouchCallback);
        itemTouchHelper.attachToRecyclerView(mRecyclerView);

It is throwing

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.graphics.Bitmap.isRecycled()' on a null object reference

Full StackTrace

09-12 01:28:58.386 26575-26575/com.ozuf.booker E/AndroidRuntime: FATAL EXCEPTION: main
                                                                     Process: com.ozuf.booker, PID: 26575
                                                                     java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.graphics.Bitmap.isRecycled()' on a null object reference
                                                                         at android.graphics.Canvas.throwIfCannotDraw(Canvas.java:1281)
                                                                         at android.view.GLES20Canvas.drawBitmap(GLES20Canvas.java:620)
                                                                         at com.ozuf.booker.fragments.BookFragment$1.onChildDraw(BookFragment.java:149)
                                                                         at android.support.v7.widget.helper.ItemTouchHelper$Callback.onDraw(ItemTouchHelper.java:1956)
                                                                         at android.support.v7.widget.helper.ItemTouchHelper$Callback.access$1400(ItemTouchHelper.java:1356)
                                                                         at android.support.v7.widget.helper.ItemTouchHelper.onDraw(ItemTouchHelper.java:542)
                                                                         at android.support.v7.widget.RecyclerView.onDraw(RecyclerView.java:3373)
                                                                         at android.view.View.draw(View.java:15635)
                                                                         at android.support.v7.widget.RecyclerView.draw(RecyclerView.java:3308)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14568)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3588)
                                                                         at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3567)
                                                                         at android.view.View.updateDisplayListIfDirty(View.java:14528)
                                                                         at android.view.View.getDisplayList(View.java:14590)
                                                                         at android.view.ThreadedRenderer.updateViewTreeDisplayList(ThreadedRenderer.java:273)
                                                                         at android.view.ThreadedRenderer.updateRootDisplayList(ThreadedRenderer.java:279)
                                                                         at android.view.ThreadedRenderer.draw(ThreadedRenderer.java:318)
                                                                         at android.view.ViewRootImpl.draw(ViewRootImpl.java:2575)
                                                                         at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2385)
                                                                         at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2012)
                                                                         at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1073)
                                                                         at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5988)
                                                                         at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
                                                                        at android.view.Choreographer.doCallbacks(Chor

Line 149 is c.drawBitmap(icon,null,icon_dest,p); I have debugged and I saw that icon is null but I don't understand why it;s null since I've already assigned it a value.

Answer 1

I don't understand why it;s null since I've already assigned it a value.

Yes. You did => null . The problem is elsewhere. See docs for decodeResource() :

Returns: The decoded bitmap, or null if the image could not be decoded .

so you need to a) always check for that condition, b) check why exactly it happens with the data you try to decode.

Answer 2

The error is because of the drawable might be a Vector.

Drawable drawable = ContextCompat.getDrawable(StreamActivity.this,R.drawable.ic_close)
Bitmap icon = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(icon);
drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
drawable.draw(canvas);

Answer 3

Trying to decode a vector drawable into Bitmap, gives such error. So try to use any image with format .png, .jpeg etc in case of decoding resource to Bitmap.

Answer 4

Answer is check if bitmap is null or reycled() before passing it to ImageView.

if(resource!==null && !resource.isRecycled)
    imageView.setImageBitmap(resource)

Answer 5

My problem was that android added a vector drawable anydpi along with the multiple created image assets for the icon. I deleted the anydpi variant and it all works fine now.

Answer 6

I switched from:

android:layout_width="1095dp"
android:layout_height="1200dp"

To:

android:layout_width="wrap_content"
android:layout_height="wrap_content"

Then the error went away.

• Inspired by seekingStillness's answer