Android(安卓)RecyclerView刷新和加载
16lz
2021-01-26
在上一章中，我们了解了RecyclerView控件的基本用法，这里我们将实现RecyclerView的刷新和加载。
1. SwipeRefreshLayout下拉刷新
我们可以利用SwipeRefreshLayout控件来实现下拉刷新，详见Android SwipeRefreshLayout控件。
2. 自定义下拉刷新
我们首先创建一个下拉刷新的父类RefreshViewCreator，一般拥有四种状态，普通、下拉刷新、释放刷新和刷新。
主要方法如下
View onCreateRefreshView(Context context, ViewGroup parent)，创建刷新界面int move(int dy)，用于下拉时改变界面release(float dy)，用于释放时改变界面refreshFinish()，刷新结束，一般用于回调
具体代码如下，
public abstract class RefreshViewCreator { public final static int DONE = 0; public final static int PULL_TO_REFRESH = 1; // 下拉刷新 public final static int RELEASE_TO_REFRESH = 2; // 释放刷新 public final static int REFRESHING = 3; // 刷新 public IOnRefreshListener mListener; public RefreshViewCreator(IOnRefreshListener listener) { this.mListener = listener; } // 创建刷新界面 public abstract View onCreateRefreshView(Context context, ViewGroup parent); // 下拉时改变界面 public int move(int dy) { return 0; } // 释放时改变界面 public void release(float dy) { } // 刷新结束 public void refreshFinish() { } protected void startRefresh() { if (mListener != null) { mListener.onRefresh(); } } public interface IOnRefreshListener { void onRefresh(); }}CustomRecyclerView继承RecyclerView，默认使用LinearLayoutManager布局。
public class CustomRecyclerView extends RecyclerView { private LinearLayoutManager mLayoutManager; private RefreshViewCreator mRefreshViewCreator; private boolean mRecord; private int mLastEventY; private boolean mRefresh; private int mTouchSlop; public CustomRecyclerView(@NonNull Context context) { this(context, null); } public CustomRecyclerView(@NonNull Context context, @Nullable AttributeSet attrs) { this(context, attrs, 0); } public CustomRecyclerView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); mLayoutManager = new LinearLayoutManager(getContext(), LinearLayoutManager.VERTICAL, false); setLayoutManager(mLayoutManager); mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop(); } public void setRefreshViewCreator(RefreshViewCreator refreshViewCreator) { this.mRefreshViewCreator = refreshViewCreator; } @Override public boolean dispatchTouchEvent(MotionEvent ev) { switch (ev.getAction()) { case MotionEvent.ACTION_DOWN: record(ev); break; case MotionEvent.ACTION_MOVE: record(ev); int dy = (int) (ev.getY() - mLastEventY); mLastEventY = (int) ev.getY(); if (allowRefresh()) { if (dy > mTouchSlop) { mRefresh = true; } if (mRefresh) { int distance = mRefreshViewCreator.move(dy / 3); if (distance == 0) { ev.setAction(MotionEvent.ACTION_CANCEL); return dispatchTouchEvent(ev); } return true; } } break; case MotionEvent.ACTION_CANCEL: case MotionEvent.ACTION_UP: if (mRefresh) { mRefreshViewCreator.release((int) (ev.getY() - mLastEventY) / 3); mRefresh = false; mLastEventY = 0; mRecord = false; return true; } break; } return super.dispatchTouchEvent(ev); } private void record(MotionEvent ev) { if (allowRefresh() && !mRecord) { mLastEventY = (int) ev.getY(); mRecord = true; } } // 是否滚动到表头了 private boolean allowRefresh() { return mRefreshViewCreator != null && !canScrollVertically(-1); }}我们通过allowRefresh()方法来判断是否已经滚动到表头了，这里有个问题是canScrollVertically()方法，当direction等于-1的时候，才是判断是否可以下拉。另外如果刷新界面高度是0或者gone的时候，canScrollVertically(-1)始终返回true。
/** * Check if this view can be scrolled vertically in a certain direction. * * @param direction Negative to check scrolling up, positive to check scrolling down. * @return true if this view can be scrolled in the specified direction, false otherwise. */public boolean canScrollVertically(int direction) { final int offset = computeVerticalScrollOffset(); final int range = computeVerticalScrollRange() - computeVerticalScrollExtent(); if (range == 0) return false; if (direction < 0) { return offset > 0; } else { return offset < range - 1; }}在Activity里面，创建一个RefreshViewCreator，利用RecyclerViewAdapter加入到表头第一行，RecyclerViewAdapter可查看上一章。
private Handler mHandler = new Handler();private RefreshViewCreator mRefreshViewCreator;private RefreshViewCreator.IOnRefreshListener mListener = new RefreshViewCreator.IOnRefreshListener() { @Override public void onRefresh() { mHandler.postDelayed(new Runnable() { @Override public void run() { mRefreshViewCreator.refreshFinish(); } }, 3000); }};@Overrideprotected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_material_design_recycler_view_refresh); CustomRecyclerView recyclerView = findViewById(R.id.recycler_view); RecyclerViewAdapter adapter = new RecyclerViewAdapter(this); recyclerView.setAdapter(adapter); mRefreshViewCreator = new CustomRefreshViewCreator(mListener); recyclerView.setRefreshViewCreator(mRefreshViewCreator); adapter.addHeaderView(mRefreshViewCreator.onCreateRefreshView(this, recyclerView));}CustomRefreshViewCreator继承RefreshViewCreator，实现自定义刷新界面
public class CustomRefreshViewCreator extends RefreshViewCreator { private View mRefreshView; private ImageView mIvArrow; private ProgressBar mProgressBar; private TextView mTvRefreshTips; private String mPullToRefreshTips, mReleaseToRefreshTips, mRefreshingTips; private int mContentHeight; private int mHeadState = DONE; private int mDistance = 0; public CustomRefreshViewCreator(IOnRefreshListener listener) { super(listener); mPullToRefreshTips = "下拉刷新"; mReleaseToRefreshTips = "松开刷新"; mRefreshingTips = "正在刷新..."; } @Override public View onCreateRefreshView(Context context, ViewGroup parent) { if (mRefreshView == null) { mRefreshView = LayoutInflater.from(context).inflate(getLayoutId(), parent, false); mContentHeight = context.getResources().getDimensionPixelOffset(R.dimen.margin_dpi_50); mIvArrow = mRefreshView.findViewById(R.id.iv_arrow); mProgressBar = mRefreshView.findViewById(R.id.progress_bar_refresh); mTvRefreshTips = mRefreshView.findViewById(R.id.tv_refresh_tips); refreshFinish(); } return mRefreshView; } protected @LayoutRes int getLayoutId() { return R.layout.list_view_refresh_view; } @Override public int move(int dy) { if (mHeadState != REFRESHING) { mDistance += dy; if (mDistance < 0) { mDistance = 0; } else if (mDistance > mContentHeight + 10) { mDistance = mContentHeight + 10; } if (mDistance <= 0) { mHeadState = DONE; } else if (mDistance >= mContentHeight) { mHeadState = RELEASE_TO_REFRESH; mIvArrow.setRotation(180); } else { mHeadState = PULL_TO_REFRESH; mIvArrow.setRotation(0); } if (mHeadState == PULL_TO_REFRESH || mHeadState == RELEASE_TO_REFRESH) { int padding = mDistance - mContentHeight; mRefreshView.setPadding(0, padding > 0 ? 0 : padding, 0, 0); } changeHeaderViewByState(); } return mDistance; } @Override public void release(float dy) { if (mHeadState != REFRESHING) { mDistance += dy; if (mDistance >= mContentHeight) { mHeadState = REFRESHING; } else { mHeadState = DONE; } mDistance = 0; changeHeaderViewByState(); if (mHeadState == REFRESHING) { startRefresh(); } } } @Override public void refreshFinish() { mHeadState = DONE; changeHeaderViewByState(); } private void changeHeaderViewByState() { switch (mHeadState) { case DONE: mRefreshView.setPadding(0, -1 * mContentHeight + 1, 0, 0); mIvArrow.setVisibility(View.VISIBLE); mProgressBar.setVisibility(View.GONE); mTvRefreshTips.setText(mPullToRefreshTips); break; case PULL_TO_REFRESH: mIvArrow.setVisibility(View.VISIBLE); mProgressBar.setVisibility(View.GONE); mTvRefreshTips.setText(mPullToRefreshTips); break; case RELEASE_TO_REFRESH: mIvArrow.setVisibility(View.VISIBLE); mProgressBar.setVisibility(View.GONE); mTvRefreshTips.setText(mReleaseToRefreshTips); break; case REFRESHING: mRefreshView.setPadding(0, 0, 0, 0); mIvArrow.setVisibility(View.GONE); mProgressBar.setVisibility(View.VISIBLE); mTvRefreshTips.setText(mRefreshingTips); break; } }}刷新界面list_view_refresh_view.xml
<?xml version="1.0" encoding="utf-8"?> 显示如下
3. 自定义上拉加载
上拉加载的实现类似于刷新，同样需要上拉加载的父类LoadViewCreator
public abstract class LoadViewCreator { public final static int DONE = 0; public final static int PULL_TO_LOAD = 1; // 上拉加载 public final static int RELEASE_TO_LOAD = 2; // 释放加载 public final static int LOADING = 3; // 加载 public IOnLoadListener mListener; public LoadViewCreator(IOnLoadListener listener) { this.mListener = listener; } public abstract View onCreateLoadView(Context context, ViewGroup parent); public int move(int dy) { return 0; } public void release(float dy) { } public void loadFinish() { } protected void startLoad() { if (mListener != null) { mListener.onLoad(); } } public interface IOnLoadListener { void onLoad(); }}自定义LoadViewCreator的实现类似于CustomRefreshViewCreator，只需要注意的是我们设置bottom的padding。
mLoadView.setPadding(0, 0, 0, padding);而在CustomRecyclerView里面，同样在dispatchTouchEvent()方法里面处理事件吗，只是在调用LoadViewCreator的move()和release()`方法，需要把参数的值转换成正数。
@Overridepublic boolean dispatchTouchEvent(MotionEvent ev) { switch (ev.getAction()) { case MotionEvent.ACTION_DOWN: record(ev); break; case MotionEvent.ACTION_MOVE: record(ev); int dy = (int) (ev.getY() - mLastEventY); mLastEventY = (int) ev.getY(); if (allowRefresh()) { if (dy > mTouchSlop) { mRefresh = true; } if (mRefresh) { int distance = mRefreshViewCreator.move(dy / 3); if (distance == 0) { ev.setAction(MotionEvent.ACTION_CANCEL); return dispatchTouchEvent(ev); } return true; } } if (allowLoad()) { if (-dy > mTouchSlop) { mLoad = true; } if (mLoad) { int distance = mLoadViewCreator.move(-dy); if (distance == 0) { ev.setAction(MotionEvent.ACTION_CANCEL); return dispatchTouchEvent(ev); } return true; } } break; case MotionEvent.ACTION_CANCEL: case MotionEvent.ACTION_UP: mRecord = false; if (mRefresh) { mRefreshViewCreator.release((int) (ev.getY() - mLastEventY) / 3); mRefresh = false; mLastEventY = 0; return true; } if (mLoad) { mLoadViewCreator.release((int) (mLastEventY - ev.getY())); mLoad = false; mLastEventY = 0; return true; } break; } return super.dispatchTouchEvent(ev);}private void record(MotionEvent ev) { if ((allowRefresh() || allowLoad()) && !mRecord) { mLastEventY = (int) ev.getY(); mRecord = true; }}private boolean allowLoad() { return mLoadViewCreator != null && !canScrollVertically(1);}显示如下
4. 自动上拉加载
当用户向上翻动列表，快要到所有列表项的底部或者已经到底部的时候，可以自动加载更多的数据。为此，我们需要监听RecyclerView列表的滚动,
public void addOnScrollListener(OnScrollListener listener)同时也获取列表最下面的元素是哪一行，LinearLayoutManager为我们提供了很多接口
public int findFirstVisibleItemPosition()public int findFirstCompletelyVisibleItemPosition()public int findLastVisibleItemPosition()public int findLastCompletelyVisibleItemPosition()实现代码如下
final LinearLayoutManager layoutManager = new LinearLayoutManager(this);RecyclerView recyclerView = findViewById(R.id.recycler_view);recyclerView.setLayoutManager(layoutManager);final RecyclerViewAdapter adapter = new RecyclerViewAdapter(this);recyclerView.setAdapter(adapter);View footerView = getLayoutInflater().inflate(R.layout.list_view_load_more_view, recyclerView, false);adapter.addFooterView(footerView);recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() { @Override public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) { if (!mLoadMore && layoutManager.findLastVisibleItemPosition() == adapter.getItemCount() - 1) { mLoadMore = true; mHandler.postDelayed(new Runnable() { @Override public void run() { adapter.addContent(); mLoadMore = false; } }, 1000); } }});显示如下
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