Decorations are now measured properly

Previously first/last flags were not taken into account and
offsets were cached sometimes in LayoutParams

app/src/main/res/drawable/divider.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape xmlns:android="http://schemas.android.com/apk/res/android">
+    <size
+        android:width="30dp"
+        android:height="10dp"/>
+    <solid android:color="#ffd4d4d4"/>
+</shape>

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

@@ -3,6 +3,7 @@
 	<style name="ListItem">
 		<item name="android:layout_width">match_parent</item>
 		<item name="android:layout_height">wrap_content</item>
+		<item name="android:layout_gravity">left|center_vertical</item>
 		<item name="android:orientation">horizontal</item>
 		<item name="android:background">@drawable/material_clickable_selector</item>
 		<item name="android:padding">5dp</item>

lib/src/main/java/org/solovyev/android/views/llm/DividerItemDecoration.java

@@ -13,16 +13,24 @@
 public class DividerItemDecoration extends RecyclerView.ItemDecoration {
 
 	private Drawable divider;
+	private int dividerHeight;
+	private int dividerWidth;
 	private boolean first = false;
 	private boolean last = false;
 
 	@SuppressWarnings("UnusedDeclaration")
 	public DividerItemDecoration(Context context, AttributeSet attrs) {
 		final TypedArray a = context.obtainStyledAttributes(attrs, new int[]{android.R.attr.listDivider});
-		divider = a.getDrawable(0);
+		setDivider(a.getDrawable(0));
 		a.recycle();
 	}
 
+	private void setDivider(Drawable divider) {
+		this.divider = divider;
+		this.dividerHeight = divider == null ? 0 : divider.getIntrinsicHeight();
+		this.dividerWidth = divider == null ? 0 : divider.getIntrinsicWidth();
+	}
+
 	@SuppressWarnings("UnusedDeclaration")
 	public DividerItemDecoration(Context context, AttributeSet attrs, boolean showFirstDivider,
 								 boolean showLastDivider) {
@@ -33,7 +41,7 @@ public DividerItemDecoration(Context context, AttributeSet attrs, boolean showFi
 
 	@SuppressWarnings("UnusedDeclaration")
 	public DividerItemDecoration(Drawable divider) {
-		this.divider = divider;
+		setDivider(divider);
 	}
 
 	@SuppressWarnings("UnusedDeclaration")
@@ -47,24 +55,33 @@ public DividerItemDecoration(Drawable divider, boolean showFirstDivider,
 	@Override
 	public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
 							   RecyclerView.State state) {
-		super.getItemOffsets(outRect, view, parent, state);
 		if (divider == null) {
+			super.getItemOffsets(outRect, view, parent, state);
+			return;
+		}
+
+		final int position = ((RecyclerView.LayoutParams) view.getLayoutParams()).getViewLayoutPosition();
+		final boolean firstItem = position == 0;
+		final boolean lastItem = position == parent.getAdapter().getItemCount() - 1;
+		final boolean dividerBefore = first || !firstItem;
+		if (!dividerBefore) {
+			super.getItemOffsets(outRect, view, parent, state);
 			return;
 		}
 
 		if (getOrientation(parent) == LinearLayoutManager.VERTICAL) {
-			outRect.top = divider.getIntrinsicHeight();
-			outRect.bottom = -outRect.top;
+			outRect.top = dividerHeight;
+			outRect.bottom = last && lastItem ? dividerHeight : 0;
 		} else {
-			outRect.left = divider.getIntrinsicWidth();
-			outRect.right = -outRect.left;
+			outRect.left = dividerWidth;
+			outRect.right = last && lastItem ? dividerWidth : 0;
 		}
 	}
 
 	@Override
-	public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
+	public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
 		if (divider == null) {
-			super.onDrawOver(c, parent, state);
+			super.onDraw(c, parent, state);
 			return;
 		}
 
@@ -79,11 +96,11 @@ public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state)
 		final boolean vertical = orientation == LinearLayoutManager.VERTICAL;
 		final int size;
 		if (vertical) {
-			size = divider.getIntrinsicHeight();
+			size = dividerHeight;
 			left = parent.getPaddingLeft();
 			right = parent.getWidth() - parent.getPaddingRight();
 		} else {
-			size = divider.getIntrinsicWidth();
+			size = dividerWidth;
 			top = parent.getPaddingTop();
 			bottom = parent.getHeight() - parent.getPaddingBottom();
 		}
@@ -92,10 +109,10 @@ public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state)
 			final View child = parent.getChildAt(i);
 			final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
 			if (vertical) {
-				top = child.getTop() - params.topMargin;
+				top = child.getTop() - params.topMargin - size;
 				bottom = top + size;
 			} else {
-				left = child.getLeft() - params.leftMargin;
+				left = child.getLeft() - params.leftMargin - size;
 				right = left + size;
 			}
 			divider.setBounds(left, top, right, bottom);

lib/src/main/java/org/solovyev/android/views/llm/LinearLayoutManager.java

@@ -1,11 +1,14 @@
 package org.solovyev.android.views.llm;
 
 import android.content.Context;
+import android.graphics.Rect;
 import android.support.v4.view.ViewCompat;
 import android.support.v7.widget.RecyclerView;
 import android.util.Log;
 import android.view.View;
 
+import java.lang.reflect.Field;
+
 /**
  * {@link android.support.v7.widget.LinearLayoutManager} which wraps its content. Note that this class will always
  * wrap the content regardless of {@link android.support.v7.widget.RecyclerView} layout parameters.
@@ -18,6 +21,9 @@
  */
 public class LinearLayoutManager extends android.support.v7.widget.LinearLayoutManager {
 
+	private static boolean canMakeInsetsDirty = true;
+	private static Field insetsDirtyField = null;
+
 	private static final int CHILD_WIDTH = 0;
 	private static final int CHILD_HEIGHT = 1;
 	private static final int DEFAULT_CHILD_SIZE = 100;
@@ -28,6 +34,7 @@ public class LinearLayoutManager extends android.support.v7.widget.LinearLayoutM
 	private int childSize = DEFAULT_CHILD_SIZE;
 	private boolean hasChildSize;
 	private int overScrollMode = ViewCompat.OVER_SCROLL_ALWAYS;
+	private final Rect tmpRect = new Rect();
 
 	@SuppressWarnings("UnusedDeclaration")
 	public LinearLayoutManager(Context context) {
@@ -227,6 +234,11 @@ private void measureChild(RecyclerView.Recycler recycler, int position, int widt
 		final int hMargin = p.leftMargin + p.rightMargin;
 		final int vMargin = p.topMargin + p.bottomMargin;
 
+		// we must make insets dirty in order calculateItemDecorationsForChild to work
+		makeInsetsDirty(p);
+		// this method should be called before any getXxxDecorationXxx() methods
+		calculateItemDecorationsForChild(child, tmpRect);
+
 		final int hDecoration = getRightDecorationWidth(child) + getLeftDecorationWidth(child);
 		final int vDecoration = getTopDecorationHeight(child) + getBottomDecorationHeight(child);
 
@@ -238,6 +250,32 @@ private void measureChild(RecyclerView.Recycler recycler, int position, int widt
 		dimensions[CHILD_WIDTH] = getDecoratedMeasuredWidth(child) + p.leftMargin + p.rightMargin;
 		dimensions[CHILD_HEIGHT] = getDecoratedMeasuredHeight(child) + p.bottomMargin + p.topMargin;
 
+		// as view is recycled let's not keep old measured values
+		makeInsetsDirty(p);
 		recycler.recycleView(child);
 	}
+
+	private static void makeInsetsDirty(RecyclerView.LayoutParams p) {
+		if (!canMakeInsetsDirty) {
+			return;
+		}
+		try {
+			if (insetsDirtyField == null) {
+				insetsDirtyField = RecyclerView.LayoutParams.class.getDeclaredField("mInsetsDirty");
+				insetsDirtyField.setAccessible(true);
+			}
+			insetsDirtyField.set(p, true);
+		} catch (NoSuchFieldException e) {
+			onMakeInsertDirtyFailed();
+		} catch (IllegalAccessException e) {
+			onMakeInsertDirtyFailed();
+		}
+	}
+
+	private static void onMakeInsertDirtyFailed() {
+		canMakeInsetsDirty = false;
+		if (BuildConfig.DEBUG) {
+			Log.w("LinearLayoutManager", "Can't make LayoutParams insets dirty, decorations measurements might be incorrect");
+		}
+	}
 }