Fix the issue that margins for items added programmatically were not taken into account. (#359)

demo-playground/src/main/java/com/google/android/flexbox/FlexboxLayoutFragment.kt

@@ -57,7 +57,7 @@ class FlexboxLayoutFragment : Fragment() {
                 flexContainer.addView(textView)
             }
         } else {
-            for (i in 0..flexContainer.flexItemCount - 1) {
+            for (i in 0 until flexContainer.flexItemCount) {
                 flexContainer.getFlexItemAt(i).setOnClickListener(
                         FlexItemClickListener(activity,
                                 FlexItemChangedListenerImpl(flexContainer), i))

flexbox/src/androidTest/java/com/google/android/flexbox/test/FlexboxAndroidTest.kt

@@ -3777,6 +3777,78 @@ class FlexboxAndroidTest {
         onView(withId(R.id.text3)).check(isTopAlignedWith(withId(R.id.flexbox_layout)))
     }
 
+    @Test
+    @FlakyTest
+    @Throws(Throwable::class)
+    fun testAddItemProgrammatically_withMarginLayoutParams() {
+        val activity = activityRule.activity
+        val flexboxLayout = createFlexboxLayout(R.layout.activity_empty_children,
+        object : Configuration {
+            override fun apply(flexboxLayout: FlexboxLayout) {
+                flexboxLayout.alignItems = AlignItems.FLEX_START
+                val first = createTextView(activity, "1", 0)
+                val second = createTextView(activity, "2", 0)
+                val lp1 = ViewGroup.MarginLayoutParams(100, 100)
+                lp1.setMargins(10, 10, 10, 10)
+                val lp2 = ViewGroup.MarginLayoutParams(100, 100)
+                lp2.setMargins(20, 20, 20, 20)
+                first.layoutParams = lp1
+                second.layoutParams = lp2
+                flexboxLayout.addView(first)
+                flexboxLayout.addView(second)
+            }
+        })
+
+        assertThat(flexboxLayout.childCount, `is`(2))
+        val view1 = flexboxLayout.getChildAt(0)
+        val view2 = flexboxLayout.getChildAt(1)
+        // Assert the coordinates of the views added programmatically with margins
+        assertThat(view1.left, `is`(10))
+        assertThat(view1.top, `is`(10))
+        assertThat(view1.bottom, `is`(110))
+        assertThat(view1.right, `is`(110))
+        assertThat(view2.left, `is`(140))
+        assertThat(view2.top, `is`(20))
+        assertThat(view2.bottom, `is`(120))
+        assertThat(view2.right, `is`(240))
+    }
+
+    @Test
+    @FlakyTest
+    @Throws(Throwable::class)
+    fun testAddItemProgrammatically_withFlexboxLayoutLayoutParams() {
+        val activity = activityRule.activity
+        val flexboxLayout = createFlexboxLayout(R.layout.activity_empty_children,
+                object : Configuration {
+                    override fun apply(flexboxLayout: FlexboxLayout) {
+                        flexboxLayout.alignItems = AlignItems.FLEX_START
+                        val first = createTextView(activity, "1", 0)
+                        val second = createTextView(activity, "2", 0)
+                        val lp1 = FlexboxLayout.LayoutParams(100, 100)
+                        lp1.setMargins(10, 10, 10, 10)
+                        val lp2 = FlexboxLayout.LayoutParams(100, 100)
+                        lp2.setMargins(20, 20, 20, 20)
+                        first.layoutParams = lp1
+                        second.layoutParams = lp2
+                        flexboxLayout.addView(first)
+                        flexboxLayout.addView(second)
+                    }
+                })
+
+        assertThat(flexboxLayout.childCount, `is`(2))
+        val view1 = flexboxLayout.getChildAt(0)
+        val view2 = flexboxLayout.getChildAt(1)
+        // Assert the coordinates of the views added programmatically with margins
+        assertThat(view1.left, `is`(10))
+        assertThat(view1.top, `is`(10))
+        assertThat(view1.bottom, `is`(110))
+        assertThat(view1.right, `is`(110))
+        assertThat(view2.left, `is`(140))
+        assertThat(view2.top, `is`(20))
+        assertThat(view2.bottom, `is`(120))
+        assertThat(view2.right, `is`(240))
+    }
+
     @Throws(Throwable::class)
     private fun createFlexboxLayout(@LayoutRes activityLayoutResId: Int,
                                     configuration: Configuration = Configuration.EMPTY): FlexboxLayout {

flexbox/src/main/java/com/google/android/flexbox/FlexboxLayout.java

@@ -1106,8 +1106,13 @@ public class FlexboxLayout extends ViewGroup implements FlexContainer {
     }
 
     @Override
-    protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
-        return new LayoutParams(p);
+    protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams lp) {
+        if (lp instanceof FlexboxLayout.LayoutParams) {
+            return new FlexboxLayout.LayoutParams((FlexboxLayout.LayoutParams) lp);
+        } else if (lp instanceof MarginLayoutParams) {
+            return new FlexboxLayout.LayoutParams((MarginLayoutParams) lp);
+        }
+        return new LayoutParams(lp);
     }
 
     @FlexDirection