CoordinatorLayout，NestedScrollView，AppbarLayout源码解析

NestedScrollView.java

1.触摸事件

1 @Override
2    public boolean onTouchEvent(MotionEvent ev) {
3        initVelocityTrackerIfNotExists();
4
5        MotionEvent vtev = MotionEvent.obtain(ev);
6
7        final int actionMasked = MotionEventCompat.getActionMasked(ev);
8
9        if (actionMasked == MotionEvent.ACTION_DOWN) {
10            mNestedYOffset = 0;
11        }
12        vtev.offsetLocation(0, mNestedYOffset);
13
14        switch (actionMasked) {
15            case MotionEvent.ACTION_DOWN: {
16                //通知nested开始滚动
17                startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
18                break;
19            }
20            case MotionEvent.ACTION_MOVE:
21                //通知nested滚动
22                if (dispatchNestedPreScroll(0, deltaY, mScrollConsumed, mScrollOffset)) {
23                    deltaY -= mScrollConsumed[1];
24                    vtev.offsetLocation(0, mScrollOffset[1]);
25                    mNestedYOffset += mScrollOffset[1];
26                }
27                ...
28                if (mIsBeingDragged) {
29                    // Scroll to follow the motion event
30                    ...
31                    if (dispatchNestedScroll(0, scrolledDeltaY, 0, unconsumedY, mScrollOffset)) {
32                        mLastMotionY -= mScrollOffset[1];
33                        vtev.offsetLocation(0, mScrollOffset[1]);
34                        mNestedYOffset += mScrollOffset[1];
35                    } else if (canOverscroll) {
36                        ...
37                    }
38                }
39                break;
40              case MotionEvent.ACTION_CANCEL:
41              case MotionEvent.ACTION_UP:
42                /* Release the drag */
43                mIsBeingDragged = false;
44                mActivePointerId = INVALID_POINTER;
45                recycleVelocityTracker();
46                if (mScroller.springBack(getScrollX(), getScrollY(), 0, 0, 0, getScrollRange())) {
47                    ViewCompat.postInvalidateOnAnimation(this);
48                }
49                //通知nested滚动
50                stopNestedScroll();
51                break;
52            
53        }
54
55        if (mVelocityTracker != null) {
56            mVelocityTracker.addMovement(vtev);
57        }
58        vtev.recycle();
59        return true;
60    }

分析dispatchNestedScroll方法

1@Override
2    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed,
3            int dyUnconsumed, int[] offsetInWindow) {
4        return mChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed,
5                offsetInWindow);
6    }
7
8
9NestedScrollViewHelper
10public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
11            int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
12        if (isNestedScrollingEnabled() && mNestedScrollingParent != null) {
13            if (dxConsumed != 0 || dyConsumed != 0 || dxUnconsumed != 0 || dyUnconsumed != 0) {
14                int startX = 0;
15                int startY = 0;
16                if (offsetInWindow != null) {
17                    mView.getLocationInWindow(offsetInWindow);
18                    startX = offsetInWindow[0];
19                    startY = offsetInWindow[1];
20                }
21//调用控制器的onNestedScroll
22                ViewParentCompat.onNestedScroll(mNestedScrollingParent, mView, dxConsumed,
23                        dyConsumed, dxUnconsumed, dyUnconsumed);
24
25                if (offsetInWindow != null) {
26                    mView.getLocationInWindow(offsetInWindow);
27                    offsetInWindow[0] -= startX;
28                    offsetInWindow[1] -= startY;
29                }
30                return true;
31            } else if (offsetInWindow != null) {
32                // No motion, no dispatch. Keep offsetInWindow up to date.
33                offsetInWindow[0] = 0;
34                offsetInWindow[1] = 0;
35            }
36        }
37        return false;
38    }
39
40ViewParentCompatLollipop.java
41public static void onNestedScroll(ViewParent parent, View target, int dxConsumed,
42            int dyConsumed, int dxUnconsumed, int dyUnconsumed) {
43        try {
44            parent.onNestedScroll(target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);
45        } catch (AbstractMethodError e) {
46            Log.e(TAG, "ViewParent " + parent + " does not implement interface " +
47                    "method onNestedScroll", e);
48        }
49    }

CoordinatorLayout.java

1    public void onNestedScroll(View target, int dxConsumed, int dyConsumed,
2            int dxUnconsumed, int dyUnconsumed) {
3        final int childCount = getChildCount();
4        boolean accepted = false;
5
6        for (int i = 0; i < childCount; i++) {
7            final View view = getChildAt(i);
8            final LayoutParams lp = (LayoutParams) view.getLayoutParams();
9//判断子View是否支持NestedScroll
10            if (!lp.isNestedScrollAccepted()) {
11                continue;
12            }
13
14            final Behavior viewBehavior = lp.getBehavior();
15            if (viewBehavior != null) {
16//调用Behavior.onNestedScroll,设置子View的偏移量
17                viewBehavior.onNestedScroll(this, view, target, dxConsumed, dyConsumed,
18                        dxUnconsumed, dyUnconsumed);
19                accepted = true;
20            }
21        }
22
23        if (accepted) {
24//通知布局变话
25            dispatchOnDependentViewChanged(true);
26        }
27    }

AppbarLayout#Behavior

1@Override
2        public void onNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
3                View target, int dxConsumed, int dyConsumed,
4                int dxUnconsumed, int dyUnconsumed) {
5            if (dyUnconsumed < 0) {
6                // If the scrolling view is scrolling down but not consuming, it's probably be at
7                // the top of it's content
8//向下滚动时，调整View位置
9                scroll(coordinatorLayout, child, dyUnconsumed,
10                        -child.getDownNestedScrollRange(), 0);
11                // Set the expanding flag so that onNestedPreScroll doesn't handle any events
12                mSkipNestedPreScroll = true;
13            } else {
14                // As we're no longer handling nested scrolls, reset the skip flag
15                mSkipNestedPreScroll = false;
16            }
17        }
18
19HeaderBehavior.java
20//设置偏移量
21final int scroll(CoordinatorLayout coordinatorLayout, V header,
22            int dy, int minOffset, int maxOffset) {
23        return setHeaderTopBottomOffset(coordinatorLayout, header,
24                getTopBottomOffsetForScrollingSibling() - dy, minOffset, maxOffset);
25    }
26
27
28    int setHeaderTopBottomOffset(CoordinatorLayout parent, V header, int newOffset,
29            int minOffset, int maxOffset) {
30        final int curOffset = getTopAndBottomOffset();
31        int consumed = 0;
32
33        if (minOffset != 0 && curOffset >= minOffset && curOffset <= maxOffset) {
34            // If we have some scrolling range, and we're currently within the min and max
35            // offsets, calculate a new offset
36            newOffset = MathUtils.constrain(newOffset, minOffset, maxOffset);
37//计算有效偏移量，如果偏移量有变化则设置新的偏移量
38            if (curOffset != newOffset) {
39                setTopAndBottomOffset(newOffset);
40                // Update how much dy we have consumed
41                consumed = curOffset - newOffset;
42            }
43        }
44
45        return consumed;
46    }
47
48public boolean setTopAndBottomOffset(int offset) {
49        if (mViewOffsetHelper != null) {
50            return mViewOffsetHelper.setTopAndBottomOffset(offset);
51        } else {
52            mTempTopBottomOffset = offset;
53        }
54        return false;
55    }
56//子View在布局时创建ViewOffsetHelper
57@Override
58    public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
59        // First let lay the child out
60        layoutChild(parent, child, layoutDirection);
61
62        if (mViewOffsetHelper == null) {
63            mViewOffsetHelper = new ViewOffsetHelper(child);
64        }
65        mViewOffsetHelper.onViewLayout();
66
67        if (mTempTopBottomOffset != 0) {
68            mViewOffsetHelper.setTopAndBottomOffset(mTempTopBottomOffset);
69            mTempTopBottomOffset = 0;
70        }
71        if (mTempLeftRightOffset != 0) {
72            mViewOffsetHelper.setLeftAndRightOffset(mTempLeftRightOffset);
73            mTempLeftRightOffset = 0;
74        }
75
76        return true;
77    }