自定义RecycleView下拉刷新

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digtal_
0.3 2018.11.12 11:58* 字数 364

1.概述

Android中的下拉刷新是我们很常见的的操作,一般列表页的下拉刷新都是SwipeRefreshLayout嵌套RecycleView完成,其中的原理就是运用了NestedScrolling嵌套滚动机制,具体可参考鸿洋老师的这篇文章https://blog.csdn.net/lmj623565791/article/details/52204039.

public class SwipeRefreshLayout extends ViewGroup implements NestedScrollingParent,
        NestedScrollingChild {
public class RecyclerView extends ViewGroup implements ScrollingView, NestedScrollingChild2 {

从上可以看到SwipeRefreshLayout 实现了NestedScrollingParent,RecyclerView 实现了NestedScrollingChild2 ,我们用的最多的下拉刷新就是使用了这个机制.

2.效果展示

refresh.gif

3.具体实现

  1. 布局
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
    <com.chinamall21.mobile.study.view.ReFreshParent
        android:id="@+id/refresh"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.v7.widget.RecyclerView
            android:id="@+id/rv"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

        </android.support.v7.widget.RecyclerView>

    </com.chinamall21.mobile.study.view.ReFreshParent>
</RelativeLayout>

刷新的头部局

<?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="120dp"
              android:background="@color/colorPrimary"
              android:orientation="horizontal">

    <FrameLayout
        android:layout_gravity="center_vertical"
        android:layout_width="130dp"
        android:layout_height="wrap_content">

        <ImageView
            android:id="@+id/iv_arrow"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="70dp"
            android:src="@mipmap/icon_arrow"/>

        <ProgressBar
            android:id="@+id/pb"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="70dp"
            android:indeterminateDrawable="@drawable/progress_drawable"
            android:visibility="invisible"/>
    </FrameLayout>

    <LinearLayout
        android:id="@+id/ll_text"
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_gravity="center_vertical"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:id="@+id/tv_tip"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="下拉刷新"
            android:textColor="#fff"
            android:textSize="18sp"/>

        <TextView
            android:id="@+id/tv_time"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="5dp"
            android:textSize="13sp"
            android:text="第一次刷新"
            android:textColor="#fff"/>
    </LinearLayout>
</LinearLayout>
  1. ReFreshParent
public class ReFreshParent extends ViewGroup implements NestedScrollingParent {
    public ReFreshParent(Context context, AttributeSet attrs) {
        super(context, attrs);
        mScroller = new Scroller(context);
        View view = LayoutInflater.from(context).inflate(R.layout.rv_header, this, false);
        mProgress = view.findViewById(R.id.pb);
        mTvTip = view.findViewById(R.id.tv_tip);
        mArrow = view.findViewById(R.id.iv_arrow);
        addView(view);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        mHeader.layout(0, -mHeaderHeight, getWidth(), 0);
        mContent.layout(0, 0, getWidth(), getBottom());
    }

在构造中加载出头部局,然后添加该布局,onLayout方法中将头部局摆放到列表上

  1. 滑动操作
    嵌套滑动过程中滑动事件是由子孩子传给父布局的,这里面就是由RecycleView传过来的滑动事件,在父布局中我们只重写了这二个实现方法:
  /**
     * 父View是否允许嵌套滑动
     *
     * @param child            包含嵌套滑动父类的子View
     * @param target           实现嵌套滑动的子View
     * @param nestedScrollAxes 嵌套滑动方向,水平竖直或都支持
     */
    @Override
    public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) {
          //当前状态不是正在刷新中当前布局就可以滑动
        return mStatus != STATUS.REFRESHING;
    }

  /**
     * 嵌套滑动子View滑动之前的准备工作
     *
     * @param target   实现嵌套滑动的子View
     * @param dx       水平方向上嵌套滑动的子View滑动的总距离
     * @param dy       竖直方向上嵌套滑动的子View滑动的总距离
     * @param consumed consumed[0]水平方向与consumed[1]竖直方向上父View消耗(滑动)的距离
     */
    @Override
    public void onNestedPreScroll(View target, int dx, int dy, int[] consumed) {
         //上滑头部局逐渐隐藏
        boolean hiddenRefresh = dy > 0 && getScrollY() <= 0;
        //下滑头部局逐渐出现
        boolean showRefresh = dy < 0 && getScrollY() >= -mHeaderHeight && !ViewCompat.canScrollVertically(target, -1);

        if (getScrollY() >= -mHeaderHeight / 2) {
            mStatus = STATUS.PULLREFRESH;
        } else {
            mStatus = STATUS.RELEASEREFRESH;
        }
        refreshByStatus(mStatus);

        if (hiddenRefresh || showRefresh) {
            scrollBy(0, dy);
            consumed[1] = dy;
        }
    }

  • onStartNestedScroll方法中,如果当前状态不是正在刷新中就允许父布局可以可以接收滑动事件.
  • onNestedPreScroll方法中,上滑头部局逐渐隐藏或下滑头部局逐渐出现这二种状态下就调用scrollBy方法滑动父布局来隐藏或显示头部局.
  public boolean onTouch(View v, MotionEvent event) {
       if (event.getAction() == MotionEvent.ACTION_UP) {
           if (getScrollY() <= -mHeaderHeight / 2) {
           mStatus = STATUS.REFRESHING;
           refreshByStatus(mStatus);
           } else {
             scrollTo(0, 0);
           }
       }
           return false;
   }
  • 在手抬起的时候根据头部局的位置来判断是否刷新
  • 根据状态来动态改变头部局的展示

4. 父布局完整代码:

public class ReFreshParent extends LinearLayout implements NestedScrollingParent {
    private boolean isMeasured;
    //刷新的头部局
    private View mHeader;
    //RecycleView列表页
    private RecyclerView mContent;
    //头部局的高度
    private int mHeaderHeight;
    private Scroller mScroller;
    //进度条
    private ProgressBar mProgress;
    //刷新提示
    private TextView mTvTip;
    //指示箭头
    private ImageView mArrow;
    //上次刷新的时间
    private long mLastTime;
    private TextView mTvTime;
    private ValueAnimator mUpAnim;
    private ValueAnimator mDownAnim;

    private enum STATUS {
        //刷新中,下拉刷新,释放刷新
        REFRESHING, PULLREFRESH, RELEASEREFRESH
    }

    //当前刷新状态
    private STATUS mStatus = STATUS.PULLREFRESH;
    private STATUS mLastStatus;


    public ReFreshParent(Context context) {
        this(context, null);
    }

    public ReFreshParent(Context context, AttributeSet attrs) {
        super(context, attrs);
        mScroller = new Scroller(context);
        View view = LayoutInflater.from(context).inflate(R.layout.rv_header, this, false);
        mProgress = view.findViewById(R.id.pb);
        mTvTip = view.findViewById(R.id.tv_tip);
        mArrow = view.findViewById(R.id.iv_arrow);
        mTvTime = view.findViewById(R.id.tv_time);

        addView(view);

    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        mHeader.layout(0, -mHeaderHeight, getWidth(), 0);
        mContent.layout(0, 0, getWidth(), getBottom());
        LogUtils.LogE("getBottom =" + getBottom());
    }

    @Override
    public boolean onStartNestedScroll(@NonNull View child, @NonNull View target, int axes) {
        //当前状态不是正在刷新中当前布局就可以滑动
        return mStatus != STATUS.REFRESHING;

    }

    @Override
    public void onNestedPreScroll(@NonNull View target, int dx, int dy, @NonNull int[] consumed) {
        //上滑头部局逐渐隐藏
        boolean hiddenRefresh = dy > 0 && getScrollY() <= 0;
        //下滑头部局逐渐出现
        boolean showRefresh = dy < 0 && getScrollY() >= -mHeaderHeight && !ViewCompat.canScrollVertically(target, -1);

        if (getScrollY() >= -mHeaderHeight / 2) {
            mStatus = STATUS.PULLREFRESH;
        } else {
            mStatus = STATUS.RELEASEREFRESH;
        }
        refreshByStatus(mStatus);

        if (hiddenRefresh || showRefresh) {
            scrollBy(0, dy);
            consumed[1] = dy;
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (!isMeasured) {
            mHeader = getChildAt(0);
            mContent = (RecyclerView) getChildAt(1);
            measureChildren(widthMeasureSpec, heightMeasureSpec);
            //获取头部局的高度
            mHeaderHeight = mHeader.getMeasuredHeight();
            isMeasured = true;
            //recycleView手抬起时的监听
            mContent.setOnTouchListener(new OnTouchListener() {
                @Override
                public boolean onTouch(View v, MotionEvent event) {
                    if (event.getAction() == MotionEvent.ACTION_UP) {

                        if (getScrollY() <= -mHeaderHeight / 2) {
                            mStatus = STATUS.REFRESHING;
                            refreshByStatus(mStatus);
                        } else {
                            scrollTo(0, 0);
                        }
                    }
                    return false;
                }
            });

            mDownAnim = ValueAnimator.ofFloat(180, 360);
            mDownAnim.setDuration(500);
            mDownAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {

                    mArrow.setRotation((Float) animation.getAnimatedValue());
                }
            });

            mUpAnim = ValueAnimator.ofFloat(0, 180);
            mUpAnim.setDuration(500);
            mUpAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    mArrow.setRotation((Float) animation.getAnimatedValue());
                }
            });
        }
    }

    /**
     * 根据状态去改变
     */
    private void refreshByStatus(STATUS status) {
        if (mLastStatus != status) {
            switch (status) {
                case PULLREFRESH:
                    if (mLastStatus != null) {            
                        mTvTip.setText("下拉刷新");
                        mDownAnim.start();
                    }

                    break;
                case REFRESHING:      
                    mTvTip.setText("正在刷新");
                    mProgress.setVisibility(VISIBLE);
                    mArrow.setVisibility(INVISIBLE);
                    mLastTime = System.currentTimeMillis();
                    new Handler().postDelayed(new Runnable() {
                        @Override
                        public void run() {
                            mProgress.setVisibility(INVISIBLE);
                            mArrow.setVisibility(VISIBLE);
                            scrollTo(0, 0);
                            mStatus = STATUS.PULLREFRESH;
                            mLastStatus = null;
                            mTvTime.setText("上次刷新时间:" + formartTime(mLastTime));
                            //刷新完毕
                            if (mRefreshCompleteListener != null)
                                mRefreshCompleteListener.refreshed();
                        }
                    }, 1500);
                    break;

                case RELEASEREFRESH:    
                    mTvTip.setText("释放刷新");
                    mUpAnim.start();
                    break;
            }
            mLastStatus = status;
        }

    }

    private String formartTime(long time) {
        return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date(time));
    }

    @Override
    public void scrollTo(int x, int y) {
        if (y <= -mHeaderHeight) {
            y = -mHeaderHeight;
        } else if (y >= 0) {
            y = 0;
        }
        super.scrollTo(x, y);
    }

    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            scrollTo(0, mScroller.getCurrY());
            invalidate();
        }
    }

    public interface RefreshCompleteListener {
        void refreshed();
    }

    private RefreshCompleteListener mRefreshCompleteListener;

    public void setRefreshCompleteListener(RefreshCompleteListener refreshCompleteListener) {
        mRefreshCompleteListener = refreshCompleteListener;
    }
}

项目地址:https://github.com/digtal/recycleview-study

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