PinnedHeaderListView from Android Contacts app

Author: jfeinstein10

library/src/com/slidingmenu/lib/menu/AutoScrollListView.java

@@ -0,0 +1,117 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.slidingmenu.lib.menu;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.widget.ListView;
+
+/**
+ * A ListView that can be asked to scroll (smoothly or otherwise) to a specific
+ * position.  This class takes advantage of similar functionality that exists
+ * in {@link ListView} and enhances it.
+ */
+public class AutoScrollListView extends ListView {
+
+    /**
+     * Position the element at about 1/3 of the list height
+     */
+    private static final float PREFERRED_SELECTION_OFFSET_FROM_TOP = 0.33f;
+
+    private int mRequestedScrollPosition = -1;
+    private boolean mSmoothScrollRequested;
+
+    public AutoScrollListView(Context context) {
+        super(context);
+    }
+
+    public AutoScrollListView(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    public AutoScrollListView(Context context, AttributeSet attrs, int defStyle) {
+        super(context, attrs, defStyle);
+    }
+
+    /**
+     * Brings the specified position to view by optionally performing a jump-scroll maneuver:
+     * first it jumps to some position near the one requested and then does a smooth
+     * scroll to the requested position.  This creates an impression of full smooth
+     * scrolling without actually traversing the entire list.  If smooth scrolling is
+     * not requested, instantly positions the requested item at a preferred offset.
+     */
+    public void requestPositionToScreen(int position, boolean smoothScroll) {
+        mRequestedScrollPosition = position;
+        mSmoothScrollRequested = smoothScroll;
+        requestLayout();
+    }
+
+    @Override
+    protected void layoutChildren() {
+        super.layoutChildren();
+        if (mRequestedScrollPosition == -1) {
+            return;
+        }
+
+        final int position = mRequestedScrollPosition;
+        mRequestedScrollPosition = -1;
+
+        int firstPosition = getFirstVisiblePosition() + 1;
+        int lastPosition = getLastVisiblePosition();
+        if (position >= firstPosition && position <= lastPosition) {
+            return; // Already on screen
+        }
+
+        final int offset = (int) (getHeight() * PREFERRED_SELECTION_OFFSET_FROM_TOP);
+        if (!mSmoothScrollRequested) {
+            setSelectionFromTop(position, offset);
+
+            // Since we have changed the scrolling position, we need to redo child layout
+            // Calling "requestLayout" in the middle of a layout pass has no effect,
+            // so we call layoutChildren explicitly
+            super.layoutChildren();
+
+        } else {
+            // We will first position the list a couple of screens before or after
+            // the new selection and then scroll smoothly to it.
+            int twoScreens = (lastPosition - firstPosition) * 2;
+            int preliminaryPosition;
+            if (position < firstPosition) {
+                preliminaryPosition = position + twoScreens;
+                if (preliminaryPosition >= getCount()) {
+                    preliminaryPosition = getCount() - 1;
+                }
+                if (preliminaryPosition < firstPosition) {
+                    setSelection(preliminaryPosition);
+                    super.layoutChildren();
+                }
+            } else {
+                preliminaryPosition = position - twoScreens;
+                if (preliminaryPosition < 0) {
+                    preliminaryPosition = 0;
+                }
+                if (preliminaryPosition > lastPosition) {
+                    setSelection(preliminaryPosition);
+                    super.layoutChildren();
+                }
+            }
+
+
+            smoothScrollToPositionFromTop(position, offset);
+        }
+    }
+}