StartOffsetItemDecoration and EndOffsetItemDecoration's constructors take in an integer value for the size of an offset in pixels. DividerItemDecoration's constructor takes a Drawable for a divider.

All of these ItemDecorations should feature constructors for each a Drawable divider and an integer pixel offset.

• drawVerticalDividers crashes when I tested it with 8 items.

• Would you support equal horizontal space in left and right of items?

Depends on #6.

Javadocs should be generated whenever changes are made to master. Travis can handle this and should push updated javadocs to a GitHub pages site.

Should use ContextCompat for resources

If the recycler view + adapter manage different view types, I want to be able to specify a decorator for each.

We can simplify the GridDividerItemDecoration API by inferring the span count of the RecyclerView from its LayoutManager

GridDividerItemDecoration.drawHorizontalDividers() assumes that the number of items in the list is at least the number of columns in the grid (see View child = parent.getChildAt(i);)

private void drawHorizontalDividers(Canvas canvas, RecyclerView parent) {
    int parentTop = parent.getPaddingTop();
    int parentBottom = parent.getHeight() - parent.getPaddingBottom();

    for (int i = 0; i < mNumColumns; i++) {
        View child = parent.getChildAt(i);
        RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();

        int parentLeft = child.getRight() + params.rightMargin;
        int parentRight = parentLeft + mHorizontalDivider.getIntrinsicWidth();

        mHorizontalDivider.setBounds(parentLeft, parentTop, parentRight, parentBottom);
        mHorizontalDivider.draw(canvas);
    }
}

There needs to be a null check before the next line that assumes child is not null.

The user may want to pass a null Drawable to GridDividerItemDecoration in the case that they want to only add a horizontal or vertical divider. We should handle this case.

When I run ./gradlew assembleRelease on my application which includes com.bignerdranch.android:simple-item-decoration:1.0.0, I get the following error:

AndroidManifest.xml:23:9-36 Error:
        Attribute application@label value=(AirportList) from AndroidManifest.xml:23:9-36
        is also present at [com.bignerdranch.android:simple-item-decoration:1.0.0] AndroidManifest.xml:13:9-41 value=(@string/app_name).
        Suggestion: add 'tools:replace="android:label"' to <application> element at AndroidManifest.xml:21:5-46:19 to override.

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:processReleaseManifest'.
> Manifest merger failed : Attribute application@label value=(AirportList) from AndroidManifest.xml:23:9-36
        is also present at [com.bignerdranch.android:simple-item-decoration:1.0.0] AndroidManifest.xml:13:9-41 value=(@string/app_name).
        Suggestion: add 'tools:replace="android:label"' to <application> element at AndroidManifest.xml:21:5-46:19 to override.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 9s

For now I didn't try the workaround because I decided to implement the feature in a way that doesn't depend on simple-item-decoration, but I thought I should report the problem here in case you want to fix it. I guess app_name just needs to be removed from the AndroidManifest.xml.

This would make the desired functionality of each ItemDecoration more clear.

Current implementation iterates over all items to draw dividers, this should be limited to only the items that are on the screen, except you may have to expand to 1 item outside the items that are completely visible.

File pulled without support for this

In order for this library to be simple, we shouldn't make the user use a separate API if they are using a different LayoutManager. Let's get the LayoutManager from the parent RecyclerView in ItemDecoration.getItemOffsets and switch behavior based on it. This will allow us to fold the following implementations together:

• DividerItemDecoration <- GridDividerItemDecoration
• StartOffsetItemDecoration <- GridTopOffsetItemDecoration
• EndOffsetItemDecoration <- GridBottomOffsetItemDecoration

Moving forward with just three ItemDecorations will enhance the usefulness of Simple Item Decoration as a library, rather than a collection of samples.

We currently have no logic to handle the case in which a user reverses the layout of their LayoutManager. We should handle this case and reverse our divider addition accordingly.

The current implementation of GridDividerItemDecoration that works for vertically scrolling lists does not space the columns out correctly. This can be seen when using dividers that are similar in size to the column widths.

This is because each column gets further offset to the right and the last one runs out of space.

The issue happens in GridDividerItemDecoration.getItemOffsets(), and a fix is hopefullt to replace with the following code:

public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
    super.getItemOffsets(outRect, view, parent, state);

    int childAdapterPosition = parent.getChildAdapterPosition(view);

    // proportion the offsets correctly given a fixed width
    if (mNumColumns > 1) {
        int columnPosition = childAdapterPosition % mNumColumns;
        int nudge = Math.round((float) mHorizontalDivider.getIntrinsicWidth() / mNumColumns);

        outRect.left = columnPosition * nudge;
        outRect.right = (mNumColumns - columnPosition - 1) * nudge;
    }

    // vertical offset is constant
    boolean childIsInFirstRow = childAdapterPosition < mNumColumns;
    if (!childIsInFirstRow) {
        outRect.top = mVerticalDivider.getIntrinsicHeight();
    }
}

I am struggling to get the master branch to run properly due to #31 and #33 so cannot create a PR at this point in time, but will try to find a way around those and submit a fix correctly.

The sample app has grown into a spaghetti mess of duplicated code and callbacks. This misses the point of a sample app by adding unnecessary complexity.

AndroidManifest.xml shouldn't be needed. Also it's causing unnecessary manifest merge conflicts w/ my app.

Error:Execution failed for task ':app:processXXXXDebugManifest'.
> Manifest merger failed : Attribute application@allowBackup value=(false) from AndroidManifest.xml:28:9-36
    is also present at [com.bignerdranch.android:simple-item-decoration:1.0.0] AndroidManifest.xml:12:9-35 value=(true).
    Suggestion: add 'tools:replace="android:allowBackup"' to <application> element at AndroidManifest.xml:26:5-96:19 to override.

App crash when data count is less than columns count (if I'm using GridDividerItemDecoration)
Below log:

08-22 06:45:15.364 5852-5852/pl.myapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: pl.myapp, PID: 5852
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
at com.dgreenhalgh.android.simpleitemdecoration.grid.GridDividerItemDecoration.drawHorizontalDividers(GridDividerItemDecoration.java:84)
at com.dgreenhalgh.android.simpleitemdecoration.grid.GridDividerItemDecoration.onDraw(GridDividerItemDecoration.java:43)
at android.support.v7.widget.RecyclerView.onDraw(RecyclerView.java:3658)
at android.view.View.draw(View.java:15231)
at android.support.v7.widget.RecyclerView.draw(RecyclerView.java:3593)
at android.view.View.updateDisplayListIfDirty(View.java:14167)
at android.view.View.getDisplayList(View.java:14189)
at android.view.View.draw(View.java:14959)
at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198)
at android.view.View.updateDisplayListIfDirty(View.java:14162)
at android.view.View.getDisplayList(View.java:14189)
at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3389)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3368)
at android.view.View.updateDisplayListIfDirty(View.java:14127)
at android.view.View.getDisplayList(View.java:14189)
at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3389)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3368)
at android.view.View.updateDisplayListIfDirty(View.java:14127)
at android.view.View.getDisplayList(View.java:14189)
at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3389)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3368)
at android.view.View.updateDisplayListIfDirty(View.java:14127)
at android.view.View.getDisplayList(View.java:14189)
at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3389)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3368)
at android.view.View.updateDisplayListIfDirty(View.java:14127)
at android.view.View.getDisplayList(View.java:14189)
at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3389)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3368)
at android.view.View.updateDisplayListIfDirty(View.java:14127)
at android.view.View.getDisplayList(View.java:14189)
at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3389)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3368)
at android.view.View.updateDisplayListIfDirty(View.java:14127)
at android.view.View.getDisplayList(View.java:14189)
at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3389)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3368)
at android.view.View.updateDisplayListIfDirty(View.java:14127)
at android.view.View.getDisplayList(View.java:14189)
at android.view.ViewGroup.recreateChildDisplayList(ViewGroup.java:3389)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:3368)
at android.view.View.updateDisplayListIfDirty(View.java:14127)
at android.view.View.getDisplayList(View.java:14189)
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:2530)
at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2352)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1982)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5885)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at android.view.Choreographer.doCallbacks(Choreographer.java:580)
at android.view.Choreographer.doFrame(Choreographer.java:550)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at android.os.Handler.h

Currently divider drawing extends to the edge of the bounds of the RecyclerView, rather than keeping to the list items. If you have a non-transparent divider, you end up with the following (dividers are green):

Depends on #3.

There's a TODO waiting for project setup instructions to be added.

Is this library available as a maven dependency? Can I plop it in my gradle file?

how i can set extra space with GridDividerItemDecoration divider ?