diff --git a/README.md b/README.md index bfb2042..58cdc6e 100644 --- a/README.md +++ b/README.md @@ -2,5 +2,8 @@ Android Notes --- -1. WebView +#### 常用组件 + +1. [WebView](https://github.com/Omooo/Android-Notes/blob/master/blogs/WebView.md) +2. diff --git a/blogs/RecyclerView.md b/blogs/RecyclerView.md new file mode 100644 index 0000000..5801da9 --- /dev/null +++ b/blogs/RecyclerView.md @@ -0,0 +1,498 @@ +--- +RecyclerView +--- + +#### 目录 + +1. 思维导图 + +2. 基本使用 + + - 复杂布局的实现、添加头布局、尾布局 + - 上拉刷新、下拉加载 + +3. 高级玩法 + + - LayoutManager + + - ItemDecoration + - ItemAnimator + - ItemTouchHelper + - 结合 SnapHelper + - 万能 Adapter + +4. 源码分析系列 + + - DefaultItemAnimator + - 缓存机制 + - ListView 的 RecycleBin + - RecyclerView 的 Recycler + - 局部刷新 + - 两者区别 + +5. 其他 + + - 扩展 RecyclerView + + - 嵌套滑动 + - 与 ListView 对比 + - RecyclerView 优缺点 + - ListView 优缺点 + +6. 参考 + +#### 思维导图 + +#### 基本使用 + +##### 复杂布局的实现 + +其实就是多个 ItemType 的场景，实现起来也很简单。定义多个 ItemTpye 和 ViewHolder，在 onCreateViewHolder 中通过 itemType 返回不同的 ViewHolder，onBindViewHolder 时根据 ViewHolder 的不同在设置不同的数据，完事。 + +这里想说一下头布局和尾布局的实现方式，其实也可以用上面的方式解决，但是我们可以用一种更加优雅的方式解决，那就是使用装饰者模式来实现扩展。 + +```java +public class BaseRvAdapterWrapper extends RecyclerView.Adapter { + + private static final int TYPE_HEADER = 0; + private static final int TYPE_NORMAL = 1; + private static final int TYPE_FOOTER = 2; + private BaseRvAdapter mBaseRvAdapter; + private View mHeaderView; + private View mFooterView; + + public BaseRvAdapterWrapper(BaseRvAdapter baseRvAdapter) { + mBaseRvAdapter = baseRvAdapter; + } + + public void setHeaderView(View headerView) { + mHeaderView = headerView; + } + + public void setFooterView(View footerView) { + mFooterView = footerView; + } + + @NonNull + @Override + public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) { + if (i == TYPE_HEADER) { + return new RecyclerView.ViewHolder(mHeaderView) { + }; + } else if (i == TYPE_NORMAL) { + return mBaseRvAdapter.onCreateViewHolder(viewGroup, i); + } else { + return new RecyclerView.ViewHolder(mFooterView) { + }; + } + } + + @Override + public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int i) { + if (i == 0 || i == mBaseRvAdapter.getItemCount() + 1) { + return; + } else { + mBaseRvAdapter.onBindViewHolder((BaseRvAdapter.MyViewHolder) viewHolder, i - 1); + } + } + + @Override + public int getItemCount() { + return mBaseRvAdapter.getItemCount() + 2; + } + + @Override + public int getItemViewType(int position) { + if (position == 0) { + return TYPE_HEADER; + } else if (position == mBaseRvAdapter.getItemCount() + 1) { + return TYPE_FOOTER; + } else { + return TYPE_NORMAL; + } + } +} +``` + +BaseRvAdapter 就是我们平常写的最基本的 Adapter，ItemView 都一样的时候。 + +关于复杂布局，其实也可以参考阿里开源的 V-Layout，不过它是内置了很多自定义 LayoutManager。 + +##### 上拉刷新、下拉加载 + +#### 高级玩法 + +##### LayoutManager + +常见实现类（LinearLayoutManager、GridLayoutManager、StaggeredGridLayoutManager），下面列出 LayoutManager 常用的 API： + +```java +canScrollHorizontally();//能否横向滚动 +canScrollVertically();//能否纵向滚动 +scrollToPosition(int position);//滚动到指定位置 + +setOrientation(int orientation);//设置滚动的方向 +getOrientation();//获取滚动方向 + +findViewByPosition(int position);//获取指定位置的Item View +findFirstCompletelyVisibleItemPosition();//获取第一个完全可见的Item位置 +findFirstVisibleItemPosition();//获取第一个可见Item的位置 +findLastCompletelyVisibleItemPosition();//获取最后一个完全可见的Item位置 +findLastVisibleItemPosition();//获取最后一个可见Item的位置 +``` + +自定义 LayoutManager： + +##### ItemDecoration + +RecyclerView 通过 addItemDecoration 方法添加 Item 之间的分割线，高版本 Android 已经提供默认实现，想改的话只需要 copy 一下这个类改一下 Drawable 即可。 + +```java +public class DividerItemDecoration extends ItemDecoration { + public static final int HORIZONTAL = 0; + public static final int VERTICAL = 1; + private static final String TAG = "DividerItem"; + private static final int[] ATTRS = new int[]{16843284}; + private Drawable mDivider; + private int mOrientation; + private final Rect mBounds = new Rect(); + + public DividerItemDecoration(Context context, int orientation) { + TypedArray a = context.obtainStyledAttributes(ATTRS); + this.mDivider = a.getDrawable(0); + if (this.mDivider == null) { + Log.w("DividerItem", "@android:attr/listDivider was not set in the theme used for this DividerItemDecoration. Please set that attribute all call setDrawable()"); + } + + a.recycle(); + this.setOrientation(orientation); + } + + public void setOrientation(int orientation) { + if (orientation != 0 && orientation != 1) { + throw new IllegalArgumentException("Invalid orientation. It should be either HORIZONTAL or VERTICAL"); + } else { + this.mOrientation = orientation; + } + } + + public void setDrawable(@NonNull Drawable drawable) { + if (drawable == null) { + throw new IllegalArgumentException("Drawable cannot be null."); + } else { + this.mDivider = drawable; + } + } + + public void onDraw(Canvas c, RecyclerView parent, State state) { + if (parent.getLayoutManager() != null && this.mDivider != null) { + if (this.mOrientation == 1) { + this.drawVertical(c, parent); + } else { + this.drawHorizontal(c, parent); + } + + } + } + + private void drawVertical(Canvas canvas, RecyclerView parent) { + canvas.save(); + int left; + int right; + if (parent.getClipToPadding()) { + left = parent.getPaddingLeft(); + right = parent.getWidth() - parent.getPaddingRight(); + canvas.clipRect(left, parent.getPaddingTop(), right, parent.getHeight() - parent.getPaddingBottom()); + } else { + left = 0; + right = parent.getWidth(); + } + + int childCount = parent.getChildCount(); + + for(int i = 0; i < childCount; ++i) { + View child = parent.getChildAt(i); + parent.getDecoratedBoundsWithMargins(child, this.mBounds); + int bottom = this.mBounds.bottom + Math.round(child.getTranslationY()); + int top = bottom - this.mDivider.getIntrinsicHeight(); + this.mDivider.setBounds(left, top, right, bottom); + this.mDivider.draw(canvas); + } + + canvas.restore(); + } + + private void drawHorizontal(Canvas canvas, RecyclerView parent) { + canvas.save(); + int top; + int bottom; + if (parent.getClipToPadding()) { + top = parent.getPaddingTop(); + bottom = parent.getHeight() - parent.getPaddingBottom(); + canvas.clipRect(parent.getPaddingLeft(), top, parent.getWidth() - parent.getPaddingRight(), bottom); + } else { + top = 0; + bottom = parent.getHeight(); + } + + int childCount = parent.getChildCount(); + + for(int i = 0; i < childCount; ++i) { + View child = parent.getChildAt(i); + parent.getLayoutManager().getDecoratedBoundsWithMargins(child, this.mBounds); + int right = this.mBounds.right + Math.round(child.getTranslationX()); + int left = right - this.mDivider.getIntrinsicWidth(); + this.mDivider.setBounds(left, top, right, bottom); + this.mDivider.draw(canvas); + } + + canvas.restore(); + } + + public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) { + if (this.mDivider == null) { + outRect.set(0, 0, 0, 0); + } else { + if (this.mOrientation == 1) { + outRect.set(0, 0, 0, this.mDivider.getIntrinsicHeight()); + } else { + outRect.set(0, 0, this.mDivider.getIntrinsicWidth(), 0); + } + + } + } +} +``` + +[DividerItemDecoration](https://android.googlesource.com/platform/development/+/cc33d7e/samples/Support7Demos/src/com/example/android/supportv7/widget/decorator/DividerItemDecoration.java) + +##### ItemAnimator + +RecyclerView 通过 setItemAnimator 方法设置添加、删除、移动、改变的动画效果。 + +RecyclerView 提供了默认的 ItemAnimator 实现类：DefaultItemAnimator。 + +DefaultItemAnimator 是继承至 SimpleItemAnimator 类，而 SimpleItemAnimator 继承至 ItemAnimator。在自定义 ItemAnimator 时只需要继承 SimpleItemAnimator 即可，因为该类提供的 API 更加清晰易懂。 + +继承 SimpleItemAnimator 需要实现的方法有： + +```java + //在 SimpleItemAnimator 中定义的抽象方法 + + //当 Item 移除时调用 + public abstract boolean animateRemove(ViewHolder var1); + //当 Item 添加时调用 + public abstract boolean animateAdd(ViewHolder var1); + //当 Item 移动时调用 + public abstract boolean animateMove(ViewHolder var1, int var2, int var3, int var4, int var5); + //当显式调用 notifyItemChanged() 或 notifyDataSetChanged() 时被调用 + public abstract boolean animateChange(ViewHolder var1, ViewHolder var2, int var3, int var4, int var5, int var6); + + //在 ItemAnimator 中定义的抽象方法 + + //执行动画 + //RecyclerView 动画的执行方式并不是立即执行，而是每帧执行一次， + //比如两帧之间添加了多个 Item，则会将这些要执行的动画 Pending 住，保存在成员变量中 + //等到下一帧一起执行，该方法的执行前提是前面 animatorXxx 返回 true + public abstract void runPendingAnimations(); + //当 Item 动画执行完毕时调用 + public abstract void endAnimation(@NonNull RecyclerView.ViewHolder var1); + //当所有动画执行完毕时调用 + public abstract void endAnimations(); + //是否有动画在执行或者将要执行 + public abstract boolean isRunning(); +``` + +##### ItemTouchHelper + +##### 结合 SnapHelper + +##### 万能 Adapter + +#### 源码分析系列 + +##### DefaultItemAnimator + +DefaultItemAnimator 类是 Android 提供的默认的动画类。首先看一下其成员变量： + +```java +//... +private ArrayList mPendingRemovals = new ArrayList(); +private ArrayList mPendingAdditions = new ArrayList(); +ArrayList mAddAnimations = new ArrayList(); +ArrayList mRemoveAnimations = new ArrayList(); +``` + +这里只列举了移除和添加 Item 时所需的动画，可以看出动画的执行单位是 ViewHolder，并且可以分为两类，一类是保存将要执行的动画，一类是保存当前正在执行的动画。 + +然后在看 animateRemove 和 animateAdd 方法： + +```java + public boolean animateRemove(ViewHolder holder) { + this.resetAnimation(holder); + this.mPendingRemovals.add(holder); + return true; + } + public boolean animateAdd(ViewHolder holder) { + this.resetAnimation(holder); + holder.itemView.setAlpha(0.0F); + this.mPendingAdditions.add(holder); + return true; + } +``` + +这两个方法是在移除和添加 Item 的时候会调用的方法，就是用 mPengdingXxx 来保存即将要执行的动画，值得注意的是，添加 Add 动画的时候会先把该 Item 置为全透明，这和我们设置 DefaultItemAnimator 后所看的是一致的。 + +接着就是 runPendingAnimations 方法，这个方法前面说过，就是将要执行的动画集合。源码如下： + +```java + public void runPendingAnimations() { + boolean removalsPending = !this.mPendingRemovals.isEmpty(); + boolean movesPending = !this.mPendingMoves.isEmpty(); + boolean changesPending = !this.mPendingChanges.isEmpty(); + boolean additionsPending = !this.mPendingAdditions.isEmpty(); + if (removalsPending || movesPending || additionsPending || changesPending) { + //移除 Item 动画 + Iterator var5 = this.mPendingRemovals.iterator(); + while(var5.hasNext()) { + ViewHolder holder = (ViewHolder)var5.next(); + this.animateRemoveImpl(holder); + } + + this.mPendingRemovals.clear(); + final ArrayList additions; + Runnable adder; + //移动 Item 动画 + if (movesPending) { + additions = new ArrayList(); + additions.addAll(this.mPendingMoves); + this.mMovesList.add(additions); + this.mPendingMoves.clear(); + adder = new Runnable() { + public void run() { + Iterator var1 = additions.iterator(); + + while(var1.hasNext()) { + DefaultItemAnimator.MoveInfo moveInfo = (DefaultItemAnimator.MoveInfo)var1.next(); + DefaultItemAnimator.this.animateMoveImpl(moveInfo.holder, moveInfo.fromX, moveInfo.fromY, moveInfo.toX, moveInfo.toY); + } + + additions.clear(); + DefaultItemAnimator.this.mMovesList.remove(additions); + } + }; + if (removalsPending) { + View view = ((DefaultItemAnimator.MoveInfo)additions.get(0)).holder.itemView; + ViewCompat.postOnAnimationDelayed(view, adder, this.getRemoveDuration()); + } else { + adder.run(); + } + } + + if (changesPending) { + additions = new ArrayList(); + additions.addAll(this.mPendingChanges); + this.mChangesList.add(additions); + this.mPendingChanges.clear(); + adder = new Runnable() { + public void run() { + Iterator var1 = additions.iterator(); + + while(var1.hasNext()) { + DefaultItemAnimator.ChangeInfo change = (DefaultItemAnimator.ChangeInfo)var1.next(); + DefaultItemAnimator.this.animateChangeImpl(change); + } + + additions.clear(); + DefaultItemAnimator.this.mChangesList.remove(additions); + } + }; + if (removalsPending) { + ViewHolder holder = ((DefaultItemAnimator.ChangeInfo)additions.get(0)).oldHolder; + ViewCompat.postOnAnimationDelayed(holder.itemView, adder, this.getRemoveDuration()); + } else { + adder.run(); + } + } + + if (additionsPending) { + additions = new ArrayList(); + additions.addAll(this.mPendingAdditions); + this.mAdditionsList.add(additions); + this.mPendingAdditions.clear(); + adder = new Runnable() { + public void run() { + Iterator var1 = additions.iterator(); + + while(var1.hasNext()) { + ViewHolder holder = (ViewHolder)var1.next(); + DefaultItemAnimator.this.animateAddImpl(holder); + } + + additions.clear(); + DefaultItemAnimator.this.mAdditionsList.remove(additions); + } + }; + if (!removalsPending && !movesPending && !changesPending) { + adder.run(); + } else { + long removeDuration = removalsPending ? this.getRemoveDuration() : 0L; + long moveDuration = movesPending ? this.getMoveDuration() : 0L; + long changeDuration = changesPending ? this.getChangeDuration() : 0L; + long totalDelay = removeDuration + Math.max(moveDuration, changeDuration); + View view = ((ViewHolder)additions.get(0)).itemView; + ViewCompat.postOnAnimationDelayed(view, adder, totalDelay); + } + } + + } + } +``` + +可以看出 Remove 动画的是最先执行的，然后依次是 Move 动画、Change 动画、Add 动画。 + +然后通过 Iterator 迭代器遍历 List 执行动画，显然真正执行动画的逻辑肯定就在 animateXxxImpl 方法里面了。 + +但是细心的你肯定会发现，为什么除了 Remove 动画，其他都需要在 Runnable 里构造执行体呢？ + +从 Runnable 的 run 方法的执行条件可以看出，如果有 Remove 动画，那么其他动画必须延时执行，如果没有，那就立即执行。 + +然后就可以看看动画真正的实现了，这里就拿 Add 动画为例，即 animateAddImpl： + +```java + void animateAddImpl(final ViewHolder holder) { + final View view = holder.itemView; + final ViewPropertyAnimator animation = view.animate(); + this.mAddAnimations.add(holder); + animation.alpha(1.0F).setDuration(this.getAddDuration()).setListener(new AnimatorListenerAdapter() { + public void onAnimationStart(Animator animator) { + DefaultItemAnimator.this.dispatchAddStarting(holder); + } + + public void onAnimationCancel(Animator animator) { + view.setAlpha(1.0F); + } + + public void onAnimationEnd(Animator animator) { + animation.setListener((AnimatorListener)null); + DefaultItemAnimator.this.dispatchAddFinished(holder); + DefaultItemAnimator.this.mAddAnimations.remove(holder); + DefaultItemAnimator.this.dispatchFinishedWhenDone(); + } + }).start(); + } +``` + +可以看到，动画真正的实现是通过 [ViewPropertyAnimator](https://developer.android.com/reference/android/view/ViewPropertyAnimator?hl=zh-cn) 来实现的，前面说到，在 Add 动画的时候会把该 ViewHolder 设置为全透明，所以这是一个透明度渐变的过程，getAddDuration 是写死的 120 毫秒，而且动画是不可逆的。 + +那我们再想想为什么不用 ObjectAnimator 来实现呢？ + +按照官方的说法，此类可以为多个同时动画提供更好的性能，而且在多个动画同时执行，并不会导致某个动画属性执行失效，并且使用更加简单。 + +此类不是由调用者构造的，而是通过 View.animate() 返回的对应 View 的 ViewPropertyAnimator 对象的引用。这给我们使用 AnimatorSet 又带来了一种新选择，get 。 + +上面都是使用 mPengdingXxx，那 mAxxAnimations 有什么 + +##### 总结： + +1. \ No newline at end of file