Android 实现锚点定位思路详解

public class CustomScrollView extends ScrollView {
 public Callbacks mCallbacks;
 public CustomScrollView(Context context) {
  super(context);
 }
 public CustomScrollView(Context context, AttributeSet attrs) {
  super(context, attrs);
 }
 public CustomScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
 }
 public void setCallbacks(Callbacks callbacks) {
  this.mCallbacks = callbacks;
 }
 @Override
 protected void onScrollChanged(int l, int t, int oldl, int oldt) {
  super.onScrollChanged(l, t, oldl, oldt);
  if (mCallbacks != null) {
   mCallbacks.onScrollChanged(l, t, oldl, oldt);
  }
 }
 //定义接口用于回调
 public interface Callbacks {
  void onScrollChanged(int x, int y, int oldx, int oldy);
 }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:app="http://schemas.android.com/apk/res-auto"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical">
 <android.support.design.widget.TabLayout
  android:id="@+id/tablayout"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  app:tabIndicatorColor="@color/colorPrimary"
  app:tabMode="scrollable"
  app:tabSelectedTextColor="@color/colorPrimary" />
 <com.tabscroll.CustomScrollView
  android:id="@+id/scrollView"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:fillViewport="true"
  android:fitsSystemWindows="true">
  <LinearLayout
   android:id="@+id/container"
   android:layout_width="match_parent"
   android:layout_height="wrap_content"
   android:orientation="vertical"
   android:padding="16dp">
  </LinearLayout>
 </com.tabscroll.CustomScrollView>
</LinearLayout>

private String[] tabTxt = {"客厅", "卧室", "餐厅", "书房", "阳台", "儿童房"};
//内容块view的集合
private List<AnchorView> anchorList = new ArrayList<>();
//判读是否是scrollview主动引起的滑动，true-是，false-否，由tablayout引起的
private boolean isScroll;
//记录上一次位置，防止在同一内容块里滑动 重复定位到tablayout
private int lastPos;
//模拟数据，填充scrollview
for (int i = 0; i < tabTxt.length; i++) {
 AnchorView anchorView = new AnchorView(this);
 anchorView.setAnchorTxt(tabTxt[i]);
 anchorView.setContentTxt(tabTxt[i]);
 anchorList.add(anchorView);
 container.addView(anchorView);
}
//tablayout设置标签
for (int i = 0; i < tabTxt.length; i++) {
 tabLayout.addTab(tabLayout.newTab().setText(tabTxt[i]));
}

public class AnchorView extends LinearLayout {
 private TextView tvAnchor;
 private TextView tvContent;
 public AnchorView(Context context) {
  this(context, null);
 }
 public AnchorView(Context context, @Nullable AttributeSet attrs) {
  this(context, attrs, 0);
 }
 public AnchorView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  init(context);
 }
 private void init(Context context) {
  View view = LayoutInflater.from(context).inflate(R.layout.view_anchor, this, true);
  tvAnchor = view.findViewById(R.id.tv_anchor);
  tvContent = view.findViewById(R.id.tv_content);
  Random random = new Random();
  int r = random.nextInt(256);
  int g = random.nextInt(256);
  int b = random.nextInt(256);
  tvContent.setBackgroundColor(Color.rgb(r, g, b));
 }
 public void setAnchorTxt(String txt) {
  tvAnchor.setText(txt);
 }
 public void setContentTxt(String txt) {
  tvContent.setText(txt);
 }
}

scrollView.setOnTouchListener(new View.OnTouchListener() {
 @Override
 public boolean onTouch(View v, MotionEvent event) {
  //当由scrollview触发时，isScroll 置true
  if (event.getAction() == MotionEvent.ACTION_DOWN) {
   isScroll = true;
  }
  return false;
 }
});
scrollView.setCallbacks(new CustomScrollView.Callbacks() {
 @Override
 public void onScrollChanged(int x, int y, int oldx, int oldy) {
  if (isScroll) {
   for (int i = tabTxt.length - 1; i >= 0; i--) {
    //根据滑动距离，对比各模块距离父布局顶部的高度判断
    if (y > anchorList.get(i).getTop() - 10) {
     setScrollPos(i);
     break;
    }
   }
  }
 }
});
//tablayout对应标签的切换
private void setScrollPos(int newPos) {
 if (lastPos != newPos) {
  //该方法不会触发tablayout 的onTabSelected 监听
  tabLayout.setScrollPosition(newPos, 0, true);
 }
 lastPos = newPos;
}
tabLayout的点击切换：
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
 @Override
 public void onTabSelected(TabLayout.Tab tab) {
  //点击标签，使scrollview滑动，isScroll置false
  isScroll = false;
  int pos = tab.getPosition();
  int top = anchorList.get(pos).getTop();
  scrollView.smoothScrollTo(0, top);
 }
 @Override
 public void onTabUnselected(TabLayout.Tab tab) {
 }
 @Override
 public void onTabReselected(TabLayout.Tab tab) {
 }
});

//监听判断最后一个模块的高度，不满一屏时让最后一个模块撑满屏幕
private ViewTreeObserver.OnGlobalLayoutListener listener;
listener = new ViewTreeObserver.OnGlobalLayoutListener() {
 @Override
 public void onGlobalLayout() {
  int screenH = getScreenHeight();
  int statusBarH = getStatusBarHeight(MainActivity.this);
  int tabH = tabLayout.getHeight();
  //计算内容块所在的高度，全屏高度-状态栏高度-tablayout的高度-内容container的padding 16dp
  int lastH = screenH - statusBarH - tabH - 16 * 3;
  AnchorView lastView = anchorList.get(anchorList.size() - 1);
  //当最后一个view 高度小于内容块高度时，设置其高度撑满
  if (lastView.getHeight() < lastH) {
   LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
   params.height = lastH;
   lastView.setLayoutParams(params);
  }
  container.getViewTreeObserver().removeOnGlobalLayoutListener(listener);

 }
};
container.getViewTreeObserver().addOnGlobalLayoutListener(listener);