CoordinatorLayout,NestedScrollView,AppbarLayout源码解析

Stella981
• 阅读 625

NestedScrollView.java

1.触摸事件

 @Override
    public boolean onTouchEvent(MotionEvent ev) {
        initVelocityTrackerIfNotExists();

        MotionEvent vtev = MotionEvent.obtain(ev);

        final int actionMasked = MotionEventCompat.getActionMasked(ev);

        if (actionMasked == MotionEvent.ACTION_DOWN) {
            mNestedYOffset = 0;
        }
        vtev.offsetLocation(0, mNestedYOffset);

        switch (actionMasked) {
            case MotionEvent.ACTION_DOWN: {
                //通知nested开始滚动
                startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
                break;
            }
            case MotionEvent.ACTION_MOVE:
                //通知nested滚动
                if (dispatchNestedPreScroll(0, deltaY, mScrollConsumed, mScrollOffset)) {
                    deltaY -= mScrollConsumed[1];
                    vtev.offsetLocation(0, mScrollOffset[1]);
                    mNestedYOffset += mScrollOffset[1];
                }
                ...
                if (mIsBeingDragged) {
                    // Scroll to follow the motion event
                    ...
                    if (dispatchNestedScroll(0, scrolledDeltaY, 0, unconsumedY, mScrollOffset)) {
                        mLastMotionY -= mScrollOffset[1];
                        vtev.offsetLocation(0, mScrollOffset[1]);
                        mNestedYOffset += mScrollOffset[1];
                    } else if (canOverscroll) {
                        ...
                    }
                }
                break;
              case MotionEvent.ACTION_CANCEL:
              case MotionEvent.ACTION_UP:
                /* Release the drag */
                mIsBeingDragged = false;
                mActivePointerId = INVALID_POINTER;
                recycleVelocityTracker();
                if (mScroller.springBack(getScrollX(), getScrollY(), 0, 0, 0, getScrollRange())) {
                    ViewCompat.postInvalidateOnAnimation(this);
                }
                //通知nested滚动
                stopNestedScroll();
                break;
            
        }

        if (mVelocityTracker != null) {
            mVelocityTracker.addMovement(vtev);
        }
        vtev.recycle();
        return true;
    }

分析dispatchNestedScroll方法

@Override
    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed,
            int dyUnconsumed, int[] offsetInWindow) {
        return mChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed,
                offsetInWindow);
    }


NestedScrollViewHelper
public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
            int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
            if (dxConsumed != 0 || dyConsumed != 0 || dxUnconsumed != 0 || dyUnconsumed != 0) {
                int startX = 0;
                int startY = 0;
                if (offsetInWindow != null) {
                    mView.getLocationInWindow(offsetInWindow);
                    startX = offsetInWindow[0];
                    startY = offsetInWindow[1];
                }
//调用控制器的onNestedScroll
                ViewParentCompat.onNestedScroll(mNestedScrollingParent, mView, dxConsumed,
                        dyConsumed, dxUnconsumed, dyUnconsumed);

                if (offsetInWindow != null) {
                    mView.getLocationInWindow(offsetInWindow);
                    offsetInWindow[0] -= startX;
                    offsetInWindow[1] -= startY;
                }
                return true;
            } else if (offsetInWindow != null) {
                // No motion, no dispatch. Keep offsetInWindow up to date.
                offsetInWindow[0] = 0;
                offsetInWindow[1] = 0;
            }
        }
        return false;
    }

ViewParentCompatLollipop.java
public static void onNestedScroll(ViewParent parent, View target, int dxConsumed,
            int dyConsumed, int dxUnconsumed, int dyUnconsumed) {
        try {
            parent.onNestedScroll(target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);
        } catch (AbstractMethodError e) {
            Log.e(TAG, "ViewParent " + parent + " does not implement interface " +
                    "method onNestedScroll", e);
        }
    }

CoordinatorLayout.java

    public void onNestedScroll(View target, int dxConsumed, int dyConsumed,
            int dxUnconsumed, int dyUnconsumed) {
        final int childCount = getChildCount();
        boolean accepted = false;

        for (int i = 0; i < childCount; i++) {
            final View view = getChildAt(i);
            final LayoutParams lp = (LayoutParams) view.getLayoutParams();
//判断子View是否支持NestedScroll
            if (!lp.isNestedScrollAccepted()) {
                continue;
            }

            final Behavior viewBehavior = lp.getBehavior();
            if (viewBehavior != null) {
//调用Behavior.onNestedScroll,设置子View的偏移量
                viewBehavior.onNestedScroll(this, view, target, dxConsumed, dyConsumed,
                        dxUnconsumed, dyUnconsumed);
                accepted = true;
            }
        }

        if (accepted) {
//通知布局变话
            dispatchOnDependentViewChanged(true);
        }
    }

AppbarLayout#Behavior

@Override
        public void onNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
                View target, int dxConsumed, int dyConsumed,
                int dxUnconsumed, int dyUnconsumed) {
            if (dyUnconsumed < 0) {
                // If the scrolling view is scrolling down but not consuming, it's probably be at
                // the top of it's content
//向下滚动时,调整View位置
                scroll(coordinatorLayout, child, dyUnconsumed,
                        -child.getDownNestedScrollRange(), 0);
                // Set the expanding flag so that onNestedPreScroll doesn't handle any events
                mSkipNestedPreScroll = true;
            } else {
                // As we're no longer handling nested scrolls, reset the skip flag
                mSkipNestedPreScroll = false;
            }
        }

HeaderBehavior.java
//设置偏移量
final int scroll(CoordinatorLayout coordinatorLayout, V header,
            int dy, int minOffset, int maxOffset) {
        return setHeaderTopBottomOffset(coordinatorLayout, header,
                getTopBottomOffsetForScrollingSibling() - dy, minOffset, maxOffset);
    }


    int setHeaderTopBottomOffset(CoordinatorLayout parent, V header, int newOffset,
            int minOffset, int maxOffset) {
        final int curOffset = getTopAndBottomOffset();
        int consumed = 0;

        if (minOffset != 0 && curOffset >= minOffset && curOffset <= maxOffset) {
            // If we have some scrolling range, and we're currently within the min and max
            // offsets, calculate a new offset
            newOffset = MathUtils.constrain(newOffset, minOffset, maxOffset);
//计算有效偏移量,如果偏移量有变化则设置新的偏移量
            if (curOffset != newOffset) {
                setTopAndBottomOffset(newOffset);
                // Update how much dy we have consumed
                consumed = curOffset - newOffset;
            }
        }

        return consumed;
    }

public boolean setTopAndBottomOffset(int offset) {
        if (mViewOffsetHelper != null) {
            return mViewOffsetHelper.setTopAndBottomOffset(offset);
        } else {
            mTempTopBottomOffset = offset;
        }
        return false;
    }
//子View在布局时创建ViewOffsetHelper
@Override
    public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
        // First let lay the child out
        layoutChild(parent, child, layoutDirection);

        if (mViewOffsetHelper == null) {
            mViewOffsetHelper = new ViewOffsetHelper(child);
        }
        mViewOffsetHelper.onViewLayout();

        if (mTempTopBottomOffset != 0) {
            mViewOffsetHelper.setTopAndBottomOffset(mTempTopBottomOffset);
            mTempTopBottomOffset = 0;
        }
        if (mTempLeftRightOffset != 0) {
            mViewOffsetHelper.setLeftAndRightOffset(mTempLeftRightOffset);
            mTempLeftRightOffset = 0;
        }

        return true;
    }
点赞
收藏
评论区
推荐文章
blmius blmius
3年前
MySQL:[Err] 1292 - Incorrect datetime value: ‘0000-00-00 00:00:00‘ for column ‘CREATE_TIME‘ at row 1
文章目录问题用navicat导入数据时,报错:原因这是因为当前的MySQL不支持datetime为0的情况。解决修改sql\mode:sql\mode:SQLMode定义了MySQL应支持的SQL语法、数据校验等,这样可以更容易地在不同的环境中使用MySQL。全局s
皕杰报表之UUID
​在我们用皕杰报表工具设计填报报表时,如何在新增行里自动增加id呢?能新增整数排序id吗?目前可以在新增行里自动增加id,但只能用uuid函数增加UUID编码,不能新增整数排序id。uuid函数说明:获取一个UUID,可以在填报表中用来创建数据ID语法:uuid()或uuid(sep)参数说明:sep布尔值,生成的uuid中是否包含分隔符'',缺省为
待兔 待兔
4个月前
手写Java HashMap源码
HashMap的使用教程HashMap的使用教程HashMap的使用教程HashMap的使用教程HashMap的使用教程22
Jacquelyn38 Jacquelyn38
3年前
2020年前端实用代码段,为你的工作保驾护航
有空的时候,自己总结了几个代码段,在开发中也经常使用,谢谢。1、使用解构获取json数据let jsonData  id: 1,status: "OK",data: 'a', 'b';let  id, status, data: number   jsonData;console.log(id, status, number )
Wesley13 Wesley13
3年前
Java获得今日零时零分零秒的时间(Date型)
publicDatezeroTime()throwsParseException{    DatetimenewDate();    SimpleDateFormatsimpnewSimpleDateFormat("yyyyMMdd00:00:00");    SimpleDateFormatsimp2newS
Wesley13 Wesley13
3年前
mysql设置时区
mysql设置时区mysql\_query("SETtime\_zone'8:00'")ordie('时区设置失败,请联系管理员!');中国在东8区所以加8方法二:selectcount(user\_id)asdevice,CONVERT\_TZ(FROM\_UNIXTIME(reg\_time),'08:00','0
Wesley13 Wesley13
3年前
00:Java简单了解
浅谈Java之概述Java是SUN(StanfordUniversityNetwork),斯坦福大学网络公司)1995年推出的一门高级编程语言。Java是一种面向Internet的编程语言。随着Java技术在web方面的不断成熟,已经成为Web应用程序的首选开发语言。Java是简单易学,完全面向对象,安全可靠,与平台无关的编程语言。
Stella981 Stella981
3年前
Django中Admin中的一些参数配置
设置在列表中显示的字段,id为django模型默认的主键list_display('id','name','sex','profession','email','qq','phone','status','create_time')设置在列表可编辑字段list_editable
Wesley13 Wesley13
3年前
MySQL部分从库上面因为大量的临时表tmp_table造成慢查询
背景描述Time:20190124T00:08:14.70572408:00User@Host:@Id:Schema:sentrymetaLast_errno:0Killed:0Query_time:0.315758Lock_
Python进阶者 Python进阶者
9个月前
Excel中这日期老是出来00:00:00,怎么用Pandas把这个去除
大家好,我是皮皮。一、前言前几天在Python白银交流群【上海新年人】问了一个Pandas数据筛选的问题。问题如下:这日期老是出来00:00:00,怎么把这个去除。二、实现过程后来【论草莓如何成为冻干莓】给了一个思路和代码如下:pd.toexcel之前把这