java - ViewHolder中View类型的字段itemView引用了什么？

Question

我试图弄清楚字段 itemView 实际上是什么。这是我从文档中获取的代码 fragment 。

public abstract static class ViewHolder {
        @NonNull
        public final View itemView;
       // others removed for simplicity
}

如果我们扩展 ViewHolder 类，因为我们还需要指定一些从 View 派生的类型字段来为每个列表项保存我们自己的小部件，那么明确 itemView 不会保存我们自己的小部件。

问题

itemView 字段引用什么？我很困惑它是否引用了 RecyclerView 还是 list_item_layout.xml 的 Root View (包含我们自己的小部件)。你能澄清一下是哪一个吗？

编辑

对于那些想了解ViewHolder内部细节的人，请参阅以下内容。我提供完整的。

public abstract static class ViewHolder {
        @NonNull
        public final View itemView;
        WeakReference<RecyclerView> mNestedRecyclerView;
        int mPosition = -1;
        int mOldPosition = -1;
        long mItemId = -1L;
        int mItemViewType = -1;
        int mPreLayoutPosition = -1;
        RecyclerView.ViewHolder mShadowedHolder = null;
        RecyclerView.ViewHolder mShadowingHolder = null;
        static final int FLAG_BOUND = 1;
        static final int FLAG_UPDATE = 2;
        static final int FLAG_INVALID = 4;
        static final int FLAG_REMOVED = 8;
        static final int FLAG_NOT_RECYCLABLE = 16;
        static final int FLAG_RETURNED_FROM_SCRAP = 32;
        static final int FLAG_IGNORE = 128;
        static final int FLAG_TMP_DETACHED = 256;
        static final int FLAG_ADAPTER_POSITION_UNKNOWN = 512;
        static final int FLAG_ADAPTER_FULLUPDATE = 1024;
        static final int FLAG_MOVED = 2048;
        static final int FLAG_APPEARED_IN_PRE_LAYOUT = 4096;
        static final int PENDING_ACCESSIBILITY_STATE_NOT_SET = -1;
        static final int FLAG_BOUNCED_FROM_HIDDEN_LIST = 8192;
        static final int FLAG_SET_A11Y_ITEM_DELEGATE = 16384;
        int mFlags;
        private static final List<Object> FULLUPDATE_PAYLOADS = Collections.emptyList();
        List<Object> mPayloads = null;
        List<Object> mUnmodifiedPayloads = null;
        private int mIsRecyclableCount = 0;
        RecyclerView.Recycler mScrapContainer = null;
        boolean mInChangeScrap = false;
        private int mWasImportantForAccessibilityBeforeHidden = 0;
        @VisibleForTesting
        int mPendingAccessibilityState = -1;
        RecyclerView mOwnerRecyclerView;

        public ViewHolder(@NonNull View itemView) {
            if (itemView == null) {
                throw new IllegalArgumentException("itemView may not be null");
            } else {
                this.itemView = itemView;
            }
        }

        void flagRemovedAndOffsetPosition(int mNewPosition, int offset, boolean applyToPreLayout) {
            this.addFlags(8);
            this.offsetPosition(offset, applyToPreLayout);
            this.mPosition = mNewPosition;
        }

        void offsetPosition(int offset, boolean applyToPreLayout) {
            if (this.mOldPosition == -1) {
                this.mOldPosition = this.mPosition;
            }

            if (this.mPreLayoutPosition == -1) {
                this.mPreLayoutPosition = this.mPosition;
            }

            if (applyToPreLayout) {
                this.mPreLayoutPosition += offset;
            }

            this.mPosition += offset;
            if (this.itemView.getLayoutParams() != null) {
                ((RecyclerView.LayoutParams)this.itemView.getLayoutParams()).mInsetsDirty = true;
            }

        }

        void clearOldPosition() {
            this.mOldPosition = -1;
            this.mPreLayoutPosition = -1;
        }

        void saveOldPosition() {
            if (this.mOldPosition == -1) {
                this.mOldPosition = this.mPosition;
            }

        }

        boolean shouldIgnore() {
            return (this.mFlags & 128) != 0;
        }

        /** @deprecated */
        @Deprecated
        public final int getPosition() {
            return this.mPreLayoutPosition == -1 ? this.mPosition : this.mPreLayoutPosition;
        }

        public final int getLayoutPosition() {
            return this.mPreLayoutPosition == -1 ? this.mPosition : this.mPreLayoutPosition;
        }

        public final int getAdapterPosition() {
            return this.mOwnerRecyclerView == null ? -1 : this.mOwnerRecyclerView.getAdapterPositionFor(this);
        }

        public final int getOldPosition() {
            return this.mOldPosition;
        }

        public final long getItemId() {
            return this.mItemId;
        }

        public final int getItemViewType() {
            return this.mItemViewType;
        }

        boolean isScrap() {
            return this.mScrapContainer != null;
        }

        void unScrap() {
            this.mScrapContainer.unscrapView(this);
        }

        boolean wasReturnedFromScrap() {
            return (this.mFlags & 32) != 0;
        }

        void clearReturnedFromScrapFlag() {
            this.mFlags &= -33;
        }

        void clearTmpDetachFlag() {
            this.mFlags &= -257;
        }

        void stopIgnoring() {
            this.mFlags &= -129;
        }

        void setScrapContainer(RecyclerView.Recycler recycler, boolean isChangeScrap) {
            this.mScrapContainer = recycler;
            this.mInChangeScrap = isChangeScrap;
        }

        boolean isInvalid() {
            return (this.mFlags & 4) != 0;
        }

        boolean needsUpdate() {
            return (this.mFlags & 2) != 0;
        }

        boolean isBound() {
            return (this.mFlags & 1) != 0;
        }

        boolean isRemoved() {
            return (this.mFlags & 8) != 0;
        }

        boolean hasAnyOfTheFlags(int flags) {
            return (this.mFlags & flags) != 0;
        }

        boolean isTmpDetached() {
            return (this.mFlags & 256) != 0;
        }

        boolean isAdapterPositionUnknown() {
            return (this.mFlags & 512) != 0 || this.isInvalid();
        }

        void setFlags(int flags, int mask) {
            this.mFlags = this.mFlags & ~mask | flags & mask;
        }

        void addFlags(int flags) {
            this.mFlags |= flags;
        }

        void addChangePayload(Object payload) {
            if (payload == null) {
                this.addFlags(1024);
            } else if ((this.mFlags & 1024) == 0) {
                this.createPayloadsIfNeeded();
                this.mPayloads.add(payload);
            }

        }

        private void createPayloadsIfNeeded() {
            if (this.mPayloads == null) {
                this.mPayloads = new ArrayList();
                this.mUnmodifiedPayloads = Collections.unmodifiableList(this.mPayloads);
            }

        }

        void clearPayload() {
            if (this.mPayloads != null) {
                this.mPayloads.clear();
            }

            this.mFlags &= -1025;
        }

        List<Object> getUnmodifiedPayloads() {
            if ((this.mFlags & 1024) == 0) {
                return this.mPayloads != null && this.mPayloads.size() != 0 ? this.mUnmodifiedPayloads : FULLUPDATE_PAYLOADS;
            } else {
                return FULLUPDATE_PAYLOADS;
            }
        }

        void resetInternal() {
            this.mFlags = 0;
            this.mPosition = -1;
            this.mOldPosition = -1;
            this.mItemId = -1L;
            this.mPreLayoutPosition = -1;
            this.mIsRecyclableCount = 0;
            this.mShadowedHolder = null;
            this.mShadowingHolder = null;
            this.clearPayload();
            this.mWasImportantForAccessibilityBeforeHidden = 0;
            this.mPendingAccessibilityState = -1;
            RecyclerView.clearNestedRecyclerViewIfNotNested(this);
        }

        void onEnteredHiddenState(RecyclerView parent) {
            if (this.mPendingAccessibilityState != -1) {
                this.mWasImportantForAccessibilityBeforeHidden = this.mPendingAccessibilityState;
            } else {
                this.mWasImportantForAccessibilityBeforeHidden = ViewCompat.getImportantForAccessibility(this.itemView);
            }

            parent.setChildImportantForAccessibilityInternal(this, 4);
        }

        void onLeftHiddenState(RecyclerView parent) {
            parent.setChildImportantForAccessibilityInternal(this, this.mWasImportantForAccessibilityBeforeHidden);
            this.mWasImportantForAccessibilityBeforeHidden = 0;
        }

        public String toString() {
            StringBuilder sb = new StringBuilder("ViewHolder{" + Integer.toHexString(this.hashCode()) + " position=" + this.mPosition + " id=" + this.mItemId + ", oldPos=" + this.mOldPosition + ", pLpos:" + this.mPreLayoutPosition);
            if (this.isScrap()) {
                sb.append(" scrap ").append(this.mInChangeScrap ? "[changeScrap]" : "[attachedScrap]");
            }

            if (this.isInvalid()) {
                sb.append(" invalid");
            }

            if (!this.isBound()) {
                sb.append(" unbound");
            }

            if (this.needsUpdate()) {
                sb.append(" update");
            }

            if (this.isRemoved()) {
                sb.append(" removed");
            }

            if (this.shouldIgnore()) {
                sb.append(" ignored");
            }

            if (this.isTmpDetached()) {
                sb.append(" tmpDetached");
            }

            if (!this.isRecyclable()) {
                sb.append(" not recyclable(" + this.mIsRecyclableCount + ")");
            }

            if (this.isAdapterPositionUnknown()) {
                sb.append(" undefined adapter position");
            }

            if (this.itemView.getParent() == null) {
                sb.append(" no parent");
            }

            sb.append("}");
            return sb.toString();
        }

        public final void setIsRecyclable(boolean recyclable) {
            this.mIsRecyclableCount = recyclable ? this.mIsRecyclableCount - 1 : this.mIsRecyclableCount + 1;
            if (this.mIsRecyclableCount < 0) {
                this.mIsRecyclableCount = 0;
                Log.e("View", "isRecyclable decremented below 0: unmatched pair of setIsRecyable() calls for " + this);
            } else if (!recyclable && this.mIsRecyclableCount == 1) {
                this.mFlags |= 16;
            } else if (recyclable && this.mIsRecyclableCount == 0) {
                this.mFlags &= -17;
            }

        }

        public final boolean isRecyclable() {
            return (this.mFlags & 16) == 0 && !ViewCompat.hasTransientState(this.itemView);
        }

        boolean shouldBeKeptAsChild() {
            return (this.mFlags & 16) != 0;
        }

        boolean doesTransientStatePreventRecycling() {
            return (this.mFlags & 16) == 0 && ViewCompat.hasTransientState(this.itemView);
        }

        boolean isUpdated() {
            return (this.mFlags & 2) != 0;
        }
    }

Answer 1

这完全取决于您的代码，因为当您调用 new SomeViewHolder(itemView) 时，它会引用 itemView。

例如Android指南-使用RecyclerView创建列表-Add a list adapter的代码中MyViewHolder 创建后有一个 TextView v 的引用。

public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent,
                                               int viewType) {
    // create a new view
    TextView v = (TextView) LayoutInflater.from(parent.getContext())
            .inflate(R.layout.my_text_view, parent, false);
    ...
    MyViewHolder vh = new MyViewHolder(v);
    return vh;
}