最近博主发现让RecyclerView滑动到某一位置并置顶的博客一大堆，抄的是完全一模一样。此外，虽然这些博客“解决”了这些问题，但这种解决方案过于浅显、粗暴，甚至都违背了开发思想。遂在此纠正这种错误。
RecyclerView提供了几种移动的方法

scrollToPosition

scrollTo

scrollBy

smoothScrollBy

smoothScrollToPosition

由于多数博客鱼龙混杂，本博客如果让你非常满意或解决了大家的根本性问题，希望多多支持在下方点赞和回复一下，举手之劳方便大家。

虽然里面有移动到指定位置的方法scrollToPosition（直接闪现至某一位位置）、smoothScrollToPosition（惯性滑动至某一位置）但是貌似都不尽人意，因为他们只保证能够展示出来，并不能保证在第一位。而此时如果你打开源码就会发现，原来全都是调用的LayoutManager移动方法，首先打开我们耳熟能详的LinearLayoutManager惊喜就在眼前

scrollToPosition
在scrollToPosition旁边有木有一个很像的方法

@Override
public void scrollToPosition(int position) {
mPendingScrollPosition = position;
mPendingScrollPositionOffset = INVALID_OFFSET;
if (mPendingSavedState != null) {
mPendingSavedState.invalidateAnchor();
}
requestLayout();
}
public void scrollToPositionWithOffset(int position, int offset) {
mPendingScrollPosition = position;
mPendingScrollPositionOffset = offset;
if (mPendingSavedState != null) {
mPendingSavedState.invalidateAnchor();
}
requestLayout();
}
当看到offset时也许就会明白：没错，这个就是item移动后相对父控件的偏移值，传入0就会有你想要的

smoothScrollToPosition
@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
int position) {
LinearSmoothScroller linearSmoothScroller =
new LinearSmoothScroller(recyclerView.getContext());
linearSmoothScroller.setTargetPosition(position);
startSmoothScroll(linearSmoothScroller);
}
而smoothScrollToPosition原来仅仅是new了一个LinearSmoothScroller然后调用startSmoothScroll

我们只需要自定义一个LinearSmoothScroller，之前写的有点仓促，仔细看LinearSmoothScroller的源码发现，其实谷歌已经埋下了伏笔，既然纠正就纠正到底吧

public class TopSmoothScroller extends LinearSmoothScroller {
TopSmoothScroller(Context context) {
super(context);
}
@Override
protected int getHorizontalSnapPreference() {
return SNAP_TO_START;//具体见源码注释
}
@Override
protected int getVerticalSnapPreference() {
return SNAP_TO_START;//具体见源码注释
}
}
然后调用LinearLayoutManager的startSmoothScroll即可

final TopSmoothScroller mScroller = new TopSmoothScroller(getActivity());
mScroller.setTargetPosition(integer);
mManager.startSmoothScroll(mScroller);
是否恍然大悟：其实我们并不需要什么bd，也不需要修改LinearLayoutManager，仅仅需要几行代码即可解决。

多看看源码，多思考思考，你也可以。

真理往往掌握在少数人手中，你是不是其中一员呢？

对于一些不会或质疑的人，此处追加demo：
public class RvHuaDongActivity extends BaseActivity {
@BindView(R.id.rv_rvhuadong)
RecyclerView mRv;
private LinearLayoutManager mManager;

//此处等于setContentView
@Override
protected int getLayouRes() {
return R.layout.activity_rv_hua_dong;
}

//此处等于onCreate
@Override
protected void initData() {
List<String> list = new ArrayList<>();
for (int i = 0; i < 100; i++) {
list.add("position" + i);
}
mManager = new LinearLayoutManager(this);
mRv.setLayoutManager(mManager);
mRv.setAdapter(new MyAdapter(list));
}

@Override
protected void setListener() {
}

@OnClick({R.id.tv_rvhuadong_GuanXing_1, R.id.tv_rvhuadong_GuanXing_2, R.id.tv_rvhuadong_GuanXing_3,
R.id.tv_rvhuadong_ShanXian_1, R.id.tv_rvhuadong_ShanXian_2, R.id.tv_rvhuadong_ShanXian_3})
public void onViewClicked(View view) {
switch (view.getId()) {
case R.id.tv_rvhuadong_GuanXing_1:
int position1 = (int) (Math.random() * 100);
Toast.makeText(this, "滑到：" + position1, Toast.LENGTH_SHORT).show();
LinearSmoothScroller s1 = new TopSmoothScroller(getActivity());
s1.setTargetPosition(position1);
mManager.startSmoothScroll(s1);
break;
case R.id.tv_rvhuadong_GuanXing_2:
LinearSmoothScroller s2 = new TopSmoothScroller(getActivity());
s2.setTargetPosition(20);
mManager.startSmoothScroll(s2);
break;
case R.id.tv_rvhuadong_GuanXing_3:
LinearSmoothScroller s3 = new TopSmoothScroller(getActivity());
s3.setTargetPosition(99);
mManager.startSmoothScroll(s3);
break;
case R.id.tv_rvhuadong_ShanXian_1:
int position2 = (int) (Math.random() * 100);
Toast.makeText(this, "闪到：" + position2, Toast.LENGTH_SHORT).show();
mManager.scrollToPositionWithOffset(position2, 0);
break;
case R.id.tv_rvhuadong_ShanXian_2:
mManager.scrollToPositionWithOffset(20, 0);
break;
case R.id.tv_rvhuadong_ShanXian_3:
mManager.scrollToPositionWithOffset(99, 0);
break;
}
}

private class MyAdapter extends RecyclerView.Adapter<BaseViewHolder> {
private final List<String> mList;

public MyAdapter(List<String> list) {
mList = list;
}

@Override
public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
LinearLayout ll = new LinearLayout(getActivity());
ll.setLayoutParams(new RecyclerView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT));
ll.setOrientation(LinearLayout.VERTICAL);

AppCompatTextView tv = new AppCompatTextView(RvHuaDongActivity.this);
tv.setTextSize(30);
tv.setBackgroundColor(0xffeeeeee);
ll.addView(tv);

RecyclerView rv = new RecyclerView(getActivity());
rv.setLayoutManager(new LinearLayoutManager(getActivity()));
rv.setNestedScrollingEnabled(true);
rv.setAdapter(new ItemAdapter(new ArrayList<String>()));
ll.addView(rv, ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
return new BaseViewHolder(ll);
}

@Override
public void onBindViewHolder(BaseViewHolder holder, int position) {
ViewGroup vg = (ViewGroup) holder.itemView;
TextView tv = (TextView) vg.getChildAt(0);
tv.setText(mList.get(position));

RecyclerView rv = (RecyclerView) vg.getChildAt(1);
ItemAdapter adapter = (ItemAdapter) rv.getAdapter();
adapter.mList.clear();
for (int i = 0; i < 6; i++) {
adapter.mList.add("item" + i);
}
adapter.notifyDataSetChanged();//在bind时确定好数据
}

@Override
public int getItemCount() {
return mList.size();
}
}

private class ItemAdapter extends RecyclerView.Adapter<BaseViewHolder> {
private final List<String> mList;

public ItemAdapter(List<String> list) {
mList = list;
}


@Override
public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
AppCompatTextView tv = new AppCompatTextView(RvHuaDongActivity.this);
tv.setTextSize(30);
tv.setBackgroundColor(0xffeeeeee);
tv.setLayoutParams(new RecyclerView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT));
return new BaseViewHolder(tv);
}

@Override
public void onBindViewHolder(BaseViewHolder holder, int position) {
TextView tv = (TextView) holder.itemView;
tv.setText(mList.get(position));
if (position >= mList.size() - 2) {
tv.getLayoutParams().height = 600;
} else {
tv.getLayoutParams().height = ViewGroup.LayoutParams.WRAP_CONTENT;
}
tv.setLayoutParams(tv.getLayoutParams());
}

@Override
public int getItemCount() {
return mList.size();
}
}

public static class TopSmoothScroller extends LinearSmoothScroller {
TopSmoothScroller(Context context) {
super(context);
}

@Override
protected int getHorizontalSnapPreference() {
return SNAP_TO_START;//具体见源码注释
}

@Override
protected int getVerticalSnapPreference() {
return SNAP_TO_START;//具体见源码注释
}
}
}
activity_rv_hua_dong.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#fff"
android:orientation="vertical">

<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
>

<TextView
android:id="@+id/tv_rvhuadong_GuanXing_1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="10dp"
android:text="惯性随机滑动"
android:textColor="#494949"
android:textSize="15sp"
/>

<TextView
android:id="@+id/tv_rvhuadong_GuanXing_2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="10dp"
android:text="惯性滑动到20"
android:textColor="#494949"
android:textSize="15sp"
/>

<TextView
android:id="@+id/tv_rvhuadong_GuanXing_3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="10dp"
android:text="惯性滑动到99"
android:textColor="#494949"
android:textSize="15sp"
/>
</LinearLayout>

<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
>

<TextView
android:id="@+id/tv_rvhuadong_ShanXian_1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="10dp"
android:text="随机闪现"
android:textColor="#494949"
android:textSize="15sp"
/>

<TextView
android:id="@+id/tv_rvhuadong_ShanXian_2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="10dp"
android:text="闪现到20"
android:textColor="#494949"
android:textSize="15sp"
/>

<TextView
android:id="@+id/tv_rvhuadong_ShanXian_3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="10dp"
android:text="闪现到99"
android:textColor="#494949"
android:textSize="15sp"
/>
</LinearLayout>

<android.support.v7.widget.RecyclerView
android:id="@+id/rv_rvhuadong"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>
support包27.0.2，目前除了startSmoothScroll进行中然后立即调用scrollToPositionWithOffset（谁会这么做）位置会出现偏差 ，其他连续调用等操作均没有任何问题

1.终于明白下面评论里的最后一个条目置顶的事了，对于类似rv嵌套rv置顶的问题（尤其是最后一个置顶）：首先你的内层rv高度（如果是竖着的）必须是wrap，为了效率和复用内层rv要在bind初始化好基本数据LayoutManager、Adapter、setNestedScrollingEnabled(true);，在外层rv bind时必须确定好你内层rv的数据（我上面的例子都有写）。

2.置顶失败的举例：①rv嵌套内层的数据需要再次请求网络动态获取的②adapter里图片高度是网络请求决定的③rv设置数据用的是handler或子线程（这3个问题的根本原因是，滑到最后一个条目了了，你还在异步加载数据，rv发现滑不动自然就把最后一个条目停在最底下了，然后你才把数据返回来早就晚了）④用了一些支持header、footer的Adapter的，条目可能需要+1才能滑到

具体的使用场景及效果可以参考微信的通讯录

转载请注明出处：王能的博客https://blog.csdn.net/weimingjue/article/details/82805361
————————————————
版权声明：本文为CSDN博主「王能」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/weimingjue/article/details/82805361