Improve the motion of indicator

Author: nshmura

CHANGELOG.md

@@ -1,6 +1,9 @@
 Change Log
 ==========
 
+## Version 1.3.0
+* Improve indicator motion
+
 ## Version 1.2.0
 * Change minSdkVersion from 9 to 14
 * Update Android SDK version to 26

README.md

@@ -35,7 +35,7 @@ repositories {
 }
 
 dependencies {
- compile 'com.nshmura:recyclertablayout:1.2.0'
+ compile 'com.nshmura:recyclertablayout:1.3.0'
 }
 ```
 

gradle.properties

@@ -1,6 +1,6 @@
 # suppress inspection "UnusedProperty" for whole file
-VERSION_NAME=1.2.0
-VERSION_CODE=13
+VERSION_NAME=1.3.0
+VERSION_CODE=14
 GROUP=com.nshmura
 ARTIFACT_ID=recyclertablayout
 ARTIFACT_NAME=RecyclerTabLayout

library/src/main/java/com/nshmura/recyclertablayout/RecyclerTabLayout.java

@@ -61,8 +61,10 @@ public class RecyclerTabLayout extends RecyclerView {
  protected Adapter<?> mAdapter;
 
  protected int mIndicatorPosition;
- protected int mIndicatorOffset;
- protected int mScrollOffset;
+ protected int mIndicatorGap;
+ protected int mIndicatorScroll;
+ private int mOldPosition;
+ private int mOldScrollOffset;
  protected float mOldPositionOffset;
  protected float mPositionThreshold;
  protected boolean mRequestScrollToTab;
@@ -248,35 +250,36 @@ protected void scrollToTab(int position, float positionOffset, boolean fitIndica
 
  if (selectedView != null) {
  int width = getMeasuredWidth();
- float scroll1 = width / 2.f - selectedView.getMeasuredWidth() / 2.f;
+ float sLeft = (position == 0) ? 0 : width / 2.f - selectedView.getMeasuredWidth() / 2.f; // left edge of selected tab
+ float sRight = sLeft + selectedView.getMeasuredWidth(); // right edge of selected tab
 
  if (nextView != null) {
- float scroll2 = width / 2.f - nextView.getMeasuredWidth() / 2.f;
-
- float scroll = scroll1 + (selectedView.getMeasuredWidth() - scroll2);
- float dx = scroll * positionOffset;
- scrollOffset = (int) (scroll1 - dx);
-
- mScrollOffset = (int) dx;
- mIndicatorOffset = (int) ((scroll1 - scroll2) * positionOffset);
+ float nLeft = width / 2.f - nextView.getMeasuredWidth() / 2.f; // left edge of next tab
+ float distance = sRight - nLeft; // total distance that is needed to distance to next tab
+ float dx = distance * positionOffset;
+ scrollOffset = (int) (sLeft - dx);
+
+ if (position == 0) {
+ float indicatorGap = (nextView.getMeasuredWidth() - selectedView.getMeasuredWidth()) / 2;
+ mIndicatorGap = (int) (indicatorGap * positionOffset);
+ mIndicatorScroll = (int)((selectedView.getMeasuredWidth() + indicatorGap) * positionOffset);
+
+ } else {
+ float indicatorGap = (nextView.getMeasuredWidth() - selectedView.getMeasuredWidth()) / 2;
+ mIndicatorGap = (int) (indicatorGap * positionOffset);
+ mIndicatorScroll = (int) dx;
+ }
 
  } else {
- scrollOffset = (int) scroll1;
- mScrollOffset = 0;
- mIndicatorOffset = 0;
+ scrollOffset = (int) sLeft;
+ mIndicatorScroll = 0;
+ mIndicatorGap = 0;
  }
  if (fitIndicator) {
- mScrollOffset = 0;
- mIndicatorOffset = 0;
- }
-
- if (mAdapter != null && mIndicatorPosition == position) {
- updateCurrentIndicatorPosition(position, positionOffset - mOldPositionOffset,
- positionOffset);
+ mIndicatorScroll = 0;
+ mIndicatorGap = 0;
  }
 
- mIndicatorPosition = position;
-
  } else {
  if (getMeasuredWidth() > 0 && mTabMaxWidth > 0 && mTabMinWidth == mTabMaxWidth) { //fixed size
  int width = mTabMinWidth;
@@ -287,13 +290,23 @@ protected void scrollToTab(int position, float positionOffset, boolean fitIndica
  mRequestScrollToTab = true;
  }
 
+ if (mAdapter != null && mIndicatorPosition != position) {
+ updateCurrentIndicatorPosition(position, positionOffset - mOldPositionOffset,
+ positionOffset);
+ }
+ mIndicatorPosition = position;
+
  stopScroll();
- mLinearLayoutManager.scrollToPositionWithOffset(position, scrollOffset);
 
+ if (position != mOldPosition || scrollOffset != mOldScrollOffset) {
+ mLinearLayoutManager.scrollToPositionWithOffset(position, scrollOffset);
+ }
  if (mIndicatorHeight > 0) {
  invalidate();
  }
 
+ mOldPosition = position;
+ mOldScrollOffset = scrollOffset;
  mOldPositionOffset = positionOffset;
  }
 
@@ -326,11 +339,11 @@ public void onDraw(Canvas canvas) {
  int left;
  int right;
  if (isLayoutRtl()) {
- left = view.getLeft() - mScrollOffset - mIndicatorOffset;
- right = view.getRight() - mScrollOffset + mIndicatorOffset;
+ left = view.getLeft() - mIndicatorScroll - mIndicatorGap;
+ right = view.getRight() - mIndicatorScroll + mIndicatorGap;
  } else {
- left = view.getLeft() + mScrollOffset - mIndicatorOffset;
- right = view.getRight() + mScrollOffset + mIndicatorOffset;
+ left = view.getLeft() + mIndicatorScroll - mIndicatorGap;
+ right = view.getRight() + mIndicatorScroll + mIndicatorGap;
  }
 
  int top = getHeight() - mIndicatorHeight;