Recyclerview源码分析（一）

Recyclerview是现在项目里使用频率越来越多的一个支持列表、网格、瀑布流的一个控件。且支持动画，支持自定义布局管理器。功能强大且灵活。同时还封装了viewHolder。但是RecyclerView是一个ViewGroup对象，所以要注意三个方法，onMeasure onLayout onDraw。

1-使用流程

通过简单使用流程，来分析每个过程都做了哪些工作。

// 创建对象
		recyclerView = this.findViewById(R.id.rv_test);
  		recyclerView.setLayoutManager(new LinearLayoutManager(this));
        RecyclerViewAdapter adapter = new RecyclerViewAdapter(this,datas);
        recyclerView.setAdapter(adapter);
 

a.创建RecyclerView对象，查看初始化对象都做了哪些工作
b.设置布局管理器，布局管理器做了什么。
c.创建适配器，适配器都有什么功能。
d.RecyclerView绑定适配器后，都有哪些逻辑，如果把数据展示出来。

2-创建RecyclerView对象

RecyclewView对象大概有7000+代码，代码量大，只看重点。

  public RecyclerView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // 创建一个观察者对象，支持监听item的移除，移动，插入，改变
        this.mObserver = new RecyclerView.RecyclerViewDataObserver();
        this.mRecycler = new RecyclerView.Recycler();
        this.mViewInfoStore = new ViewInfoStore();
        this.mUpdateChildViewsRunnable = new Runnable() {
            public void run() {
                if (RecyclerView.this.mFirstLayoutComplete && !RecyclerView.this.isLayoutRequested()) {
                    if (!RecyclerView.this.mIsAttached) {
                        RecyclerView.this.requestLayout();
                    } else if (RecyclerView.this.mLayoutFrozen) {
                        RecyclerView.this.mLayoutWasDefered = true;
                    } else {
                        RecyclerView.this.consumePendingUpdateOperations();
                    }
                }
            }
        };
        this.mTempRect = new Rect();
        this.mTempRect2 = new Rect();
        this.mTempRectF = new RectF();
        this.mItemDecorations = new ArrayList();
        this.mOnItemTouchListeners = new ArrayList();
        this.mInterceptRequestLayoutDepth = 0;
        this.mDataSetHasChangedAfterLayout = false;
        this.mDispatchItemsChangedEvent = false;
        this.mLayoutOrScrollCounter = 0;
        this.mDispatchScrollCounter = 0;
        this.mEdgeEffectFactory = new RecyclerView.EdgeEffectFactory();
        this.mItemAnimator = new DefaultItemAnimator();
        this.mScrollState = 0;
        this.mScrollPointerId = -1;
        this.mScaledHorizontalScrollFactor = 1.4E-45F;
        this.mScaledVerticalScrollFactor = 1.4E-45F;
        this.mPreserveFocusAfterLayout = true;
        this.mViewFlinger = new RecyclerView.ViewFlinger();
        this.mPrefetchRegistry = ALLOW_THREAD_GAP_WORK ? new LayoutPrefetchRegistryImpl() : null;
        this.mState = new RecyclerView.State();
        this.mItemsAddedOrRemoved = false;
        this.mItemsChanged = false;
        this.mItemAnimatorListener = new RecyclerView.ItemAnimatorRestoreListener();
        this.mPostedAnimatorRunner = false;
        this.mMinMaxLayoutPositions = new int[2];
        this.mScrollOffset = new int[2];
        this.mScrollConsumed = new int[2];
        this.mNestedOffsets = new int[2];
        this.mScrollStepConsumed = new int[2];
        this.mPendingAccessibilityImportanceChange = new ArrayList();
        this.mItemAnimatorRunner = new Runnable() {
            public void run() {
                if (RecyclerView.this.mItemAnimator != null) {
                    RecyclerView.this.mItemAnimator.runPendingAnimations();
                }

                RecyclerView.this.mPostedAnimatorRunner = false;
            }
        };
        this.mViewInfoProcessCallback = new ProcessCallback() {
            public void processDisappeared(RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ItemAnimator.ItemHolderInfo info, @Nullable RecyclerView.ItemAnimator.ItemHolderInfo postInfo) {
                RecyclerView.this.mRecycler.unscrapView(viewHolder);
                RecyclerView.this.animateDisappearance(viewHolder, info, postInfo);
            }

            public void processAppeared(RecyclerView.ViewHolder viewHolder, RecyclerView.ItemAnimator.ItemHolderInfo preInfo, RecyclerView.ItemAnimator.ItemHolderInfo info) {
                RecyclerView.this.animateAppearance(viewHolder, preInfo, info);
            }

            public void processPersistent(RecyclerView.ViewHolder viewHolder, @NonNull RecyclerView.ItemAnimator.ItemHolderInfo preInfo, @NonNull RecyclerView.ItemAnimator.ItemHolderInfo postInfo) {
                viewHolder.setIsRecyclable(false);
                if (RecyclerView.this.mDataSetHasChangedAfterLayout) {
                    if (RecyclerView.this.mItemAnimator.animateChange(viewHolder, viewHolder, preInfo, postInfo)) {
                        RecyclerView.this.postAnimationRunner();
                    }
                } else if (RecyclerView.this.mItemAnimator.animatePersistence(viewHolder, preInfo, postInfo)) {
                    RecyclerView.this.postAnimationRunner();
                }

            }

            public void unused(RecyclerView.ViewHolder viewHolder) {
                RecyclerView.this.mLayout.removeAndRecycleView(viewHolder.itemView, RecyclerView.this.mRecycler);
            }
        };
        if (attrs != null) {
            TypedArray a = context.obtainStyledAttributes(attrs, CLIP_TO_PADDING_ATTR, defStyle, 0);
            this.mClipToPadding = a.getBoolean(0, true);
            a.recycle();
        } else {
            this.mClipToPadding = true;
        }

        this.setScrollContainer(true);
        this.setFocusableInTouchMode(true);
        ViewConfiguration vc = ViewConfiguration.get(context);
        this.mTouchSlop = vc.getScaledTouchSlop();
        this.mScaledHorizontalScrollFactor = ViewConfigurationCompat.getScaledHorizontalScrollFactor(vc, context);
        this.mScaledVerticalScrollFactor = ViewConfigurationCompat.getScaledVerticalScrollFactor(vc, context);
        this.mMinFlingVelocity = vc.getScaledMinimumFlingVelocity();
        this.mMaxFlingVelocity = vc.getScaledMaximumFlingVelocity();
        this.setWillNotDraw(this.getOverScrollMode() == 2);
        this.mItemAnimator.setListener(this.mItemAnimatorListener);
        this.initAdapterManager();
        this.initChildrenHelper();
        this.initAutofill();
        if (ViewCompat.getImportantForAccessibility(this) == 0) {
            ViewCompat.setImportantForAccessibility(this, 1);
        }

        this.mAccessibilityManager = (AccessibilityManager)this.getContext().getSystemService("accessibility");
        this.setAccessibilityDelegateCompat(new RecyclerViewAccessibilityDelegate(this));
        boolean nestedScrollingEnabled = true;
        if (attrs != null) {
            int defStyleRes = 0;
            TypedArray a = context.obtainStyledAttributes(attrs, styleable.RecyclerView, defStyle, defStyleRes);
            String layoutManagerName = a.getString(styleable.RecyclerView_layoutManager);
            int descendantFocusability = a.getInt(styleable.RecyclerView_android_descendantFocusability, -1);
            if (descendantFocusability == -1) {
                this.setDescendantFocusability(262144);
            }

            this.mEnableFastScroller = a.getBoolean(styleable.RecyclerView_fastScrollEnabled, false);
            if (this.mEnableFastScroller) {
                StateListDrawable verticalThumbDrawable = (StateListDrawable)a.getDrawable(styleable.RecyclerView_fastScrollVerticalThumbDrawable);
                Drawable verticalTrackDrawable = a.getDrawable(styleable.RecyclerView_fastScrollVerticalTrackDrawable);
                StateListDrawable horizontalThumbDrawable = (StateListDrawable)a.getDrawable(styleable.RecyclerView_fastScrollHorizontalThumbDrawable);
                Drawable horizontalTrackDrawable = a.getDrawable(styleable.RecyclerView_fastScrollHorizontalTrackDrawable);
                this.initFastScroller(verticalThumbDrawable, verticalTrackDrawable, horizontalThumbDrawable, horizontalTrackDrawable);
            }

            a.recycle();
            this.createLayoutManager(context, layoutManagerName, attrs, defStyle, defStyleRes);
            if (VERSION.SDK_INT >= 21) {
                a = context.obtainStyledAttributes(attrs, NESTED_SCROLLING_ATTRS, defStyle, defStyleRes);
                nestedScrollingEnabled = a.getBoolean(0, true);
                a.recycle();
            }
        } else {
            this.setDescendantFocusability(262144);
        }

        this.setNestedScrollingEnabled(nestedScrollingEnabled);
    }