ListView源码分析
ListView源码分析
项目中使用ListView还是挺多的,之前看过几次,很是容易遗忘,今特做记录如下
- Android 6.0 & API Level 23
- Github: Nvsleep
- 邮箱: lizhenqiao@126.com
主要从以下几点进行源码分析
- 构造函数初始化
- onMeasure()
- onLayout()
- listview.setAdapter() 以及 adapter.notifyDataSetChanged()
- onInterceptTouchEvent()和onTouchEvent()
简要
ListView继承之AbsListView抽象类,所以大部分分析的源码都在这两个类中
构造函数初始化过程
父类AbsListView的初始化:
public AbsListView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
// 初始化设置一些额外属性值
initAbsListView();
mOwnerThread = Thread.currentThread();
// 初始化XML文件中设置的某些默认属性值
final TypedArray a = context.obtainStyledAttributes(
attrs, R.styleable.AbsListView, defStyleAttr, defStyleRes);
final Drawable selector = a.getDrawable(R.styleable.AbsListView_listSelector);
if (selector != null) {
setSelector(selector);
}
mDrawSelectorOnTop = a.getBoolean(R.styleable.AbsListView_drawSelectorOnTop, false);
// 初始化设置mStackFromBottom,这个影响到布局子view的顺序方式,默认为false
setStackFromBottom(a.getBoolean(
R.styleable.AbsListView_stackFromBottom, false));
setScrollingCacheEnabled(a.getBoolean(
R.styleable.AbsListView_scrollingCache, true));
setTextFilterEnabled(a.getBoolean(
R.styleable.AbsListView_textFilterEnabled, false));
setTranscriptMode(a.getInt(
R.styleable.AbsListView_transcriptMode, TRANSCRIPT_MODE_DISABLED));
setCacheColorHint(a.getColor(
R.styleable.AbsListView_cacheColorHint, 0));
setSmoothScrollbarEnabled(a.getBoolean(
R.styleable.AbsListView_smoothScrollbar, true));
setChoiceMode(a.getInt(
R.styleable.AbsListView_choiceMode, CHOICE_MODE_NONE));
setFastScrollEnabled(a.getBoolean(
R.styleable.AbsListView_fastScrollEnabled, false));
setFastScrollStyle(a.getResourceId(
R.styleable.AbsListView_fastScrollStyle, 0));
setFastScrollAlwaysVisible(a.getBoolean(
R.styleable.AbsListView_fastScrollAlwaysVisible, false));
a.recycle();
}
private void initAbsListView() {
// Setting focusable in touch mode will set the focusable property to true
// 设置ListView本身可以点击即可以消耗父View分发的事件
setClickable(true);
setFocusableInTouchMode(true);
// 因为向上父类还继承之ViewGroup,ViewGroup默认不需要重写draw()方法,
// 从而setWillNotDraw(true),但是AbsListView为了滚动效果,自身重写了View的
// draw(),主要用于实现滚动到最底部或最顶部的非OVER_SCROLL_NEVER模式的效果
setWillNotDraw(false);
setAlwaysDrawnWithCacheEnabled(false);
setScrollingCacheEnabled(true);
// 事件处理相关变量初始化
final ViewConfiguration configuration = ViewConfiguration.get(mContext);
mTouchSlop = configuration.getScaledTouchSlop();
mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
mOverscrollDistance = configuration.getScaledOverscrollDistance();
mOverflingDistance = configuration.getScaledOverflingDistance();
mDensityScale = getContext().getResources().getDisplayMetrics().density;
}ListView的初始化:
public ListView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
final TypedArray a = context.obtainStyledAttributes(
attrs, R.styleable.ListView, defStyleAttr, defStyleRes);
final CharSequence[] entries = a.getTextArray(R.styleable.ListView_entries);
if (entries != null) {
setAdapter(new ArrayAdapter<>(context, R.layout.simple_list_item_1, entries));
}
// 获取item分割线的drawable对象
final Drawable d = a.getDrawable(R.styleable.ListView_divider);
if (d != null) {
// Use an implicit divider height which may be explicitly
// overridden by android:dividerHeight further down.
setDivider(d);
}
final Drawable osHeader = a.getDrawable(R.styleable.ListView_overScrollHeader);
if (osHeader != null) {
setOverscrollHeader(osHeader);
}
final Drawable osFooter = a.getDrawable(R.styleable.ListView_overScrollFooter);
if (osFooter != null) {
setOverscrollFooter(osFooter);
}
// Use an explicit divider height, if specified.
// item分割线的高度
if (a.hasValueOrEmpty(R.styleable.ListView_dividerHeight)) {
final int dividerHeight = a.getDimensionPixelSize(
R.styleable.ListView_dividerHeight, 0);
if (dividerHeight != 0) {
setDividerHeight(dividerHeight);
}
}
mHeaderDividersEnabled = a.getBoolean(R.styleable.ListView_headerDividersEnabled, true);
mFooterDividersEnabled = a.getBoolean(R.styleable.ListView_footerDividersEnabled, true);
a.recycle();
}onMeasure()
ListView的onMeasure()方法
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// Sets up mListPadding
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
int childWidth = 0;
int childHeight = 0;
int childState = 0;
mItemCount = mAdapter == null ? 0 : mAdapter.getCount();
if (mItemCount > 0 && (widthMode == MeasureSpec.UNSPECIFIED
|| heightMode == MeasureSpec.UNSPECIFIED)) {
final View child = obtainView(0, mIsScrap);
// Lay out child directly against the parent measure spec so that
// we can obtain exected minimum width and height.
measureScrapChild(child, 0, widthMeasureSpec, heightSize);
childWidth = child.getMeasuredWidth();
childHeight = child.getMeasuredHeight();
childState = combineMeasuredStates(childState, child.getMeasuredState());
if (recycleOnMeasure() && mRecycler.shouldRecycleViewType(
((LayoutParams) child.getLayoutParams()).viewType)) {
mRecycler.addScrapView(child, 0);
}
}
if (widthMode == MeasureSpec.UNSPECIFIED) {
widthSize = mListPadding.left + mListPadding.right + childWidth +
getVerticalScrollbarWidth();
} else {
widthSize |= (childState & MEASURED_STATE_MASK);
}
if (heightMode == MeasureSpec.UNSPECIFIED) {
heightSize = mListPadding.top + mListPadding.bottom + childHeight +
getVerticalFadingEdgeLength() * 2;
}
// 有时候需要使ListView的高度等于所有子item view 可以重写onMeasure()方法使其调用以
// 下代码
if (heightMode == MeasureSpec.AT_MOST) {
// TODO: after first layout we should maybe start at the first visible position, not 0
heightSize = measureHeightOfChildren(widthMeasureSpec, 0, NO_POSITION, heightSize, -1);
}
setMeasuredDimension(widthSize, heightSize);
mWidthMeasureSpec = widthMeasureSpec;
}整体上ListView的onMeasure方法比较简单,普通.
onLayout()
ListView由adapter.getView()获取的子view的layout方式在此实现
父类AbsListView的onLayout():
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
mInLayout = true;
final int childCount = getChildCount();
if (changed) {
for (int i = 0; i < childCount; i++) {
getChildAt(i).forceLayout();
}
mRecycler.markChildrenDirty();
}
// 由子类ListView 和 GridView实现,是核心布局方法代码,也是listview与adapter交互数据
// 的主要入口函数
layoutChildren();
mInLayout = false;
mOverscrollMax = (b - t) / OVERSCROLL_LIMIT_DIVISOR;
// TODO: Move somewhere sane. This doesn't belong in onLayout().
if (mFastScroll != null) {
mFastScroll.onItemCountChanged(getChildCount(), mItemCount);
}
}ListView的layoutChildren():
@Override
protected void layoutChildren() {
final boolean blockLayoutRequests = mBlockLayoutRequests;
if (blockLayoutRequests) {
return;
}
mBlockLayoutRequests = true;
try {
super.layoutChildren();
invalidate();
if (mAdapter == null) {
resetList();
invokeOnItemScrollListener();
return;
}
final int childrenTop = mListPadding.top;
final int childrenBottom = mBottom - mTop - mListPadding.bottom;
// 每次即将进行layout子item view的时候先记录当前listview已有的child view个数
final int childCount = getChildCount();
int index = 0;
int delta = 0;
View sel;
View oldSel = null;
View oldFirst = null;
View newSel = null;
// Remember stuff we will need down below
switch (mLayoutMode) {
case LAYOUT_SET_SELECTION:
index = mNextSelectedPosition - mFirstPosition;
if (index >= 0 && index < childCount) {
newSel = getChildAt(index);
}
break;
case LAYOUT_FORCE_TOP:
case LAYOUT_FORCE_BOTTOM:
case LAYOUT_SPECIFIC:
case LAYOUT_SYNC:
break;
case LAYOUT_MOVE_SELECTION:
default:
// Remember the previously selected view
index = mSelectedPosition - mFirstPosition;
if (index >= 0 && index < childCount) {
oldSel = getChildAt(index);
}
// Remember the previous first child
oldFirst = getChildAt(0);
if (mNextSelectedPosition >= 0) {
delta = mNextSelectedPosition - mSelectedPosition;
}
// Caution: newSel might be null
newSel = getChildAt(index + delta);
}
boolean dataChanged = mDataChanged;
if (dataChanged) {
handleDataChanged();
}
// Handle the empty set by removing all views that are visible
// and calling it a day
if (mItemCount == 0) {
resetList();
invokeOnItemScrollListener();
return;
} else if (mItemCount != mAdapter.getCount()) {
throw new IllegalStateException("The content of the adapter has changed but "
+ "ListView did not receive a notification. Make sure the content of "
+ "your adapter is not modified from a background thread, but only from "
+ "the UI thread. Make sure your adapter calls notifyDataSetChanged() "
+ "when its content changes. [in ListView(" + getId() + ", " + getClass()
+ ") with Adapter(" + mAdapter.getClass() + ")]");
}
setSelectedPositionInt(mNextSelectedPosition);
AccessibilityNodeInfo accessibilityFocusLayoutRestoreNode = null;
View accessibilityFocusLayoutRestoreView = null;
int accessibilityFocusPosition = INVALID_POSITION;
// Remember which child, if any, had accessibility focus. This must
// occur before recycling any views, since that will clear
// accessibility focus.
final ViewRootImpl viewRootImpl = getViewRootImpl();
if (viewRootImpl != null) {
final View focusHost = viewRootImpl.getAccessibilityFocusedHost();
if (focusHost != null) {
final View focusChild = getAccessibilityFocusedChild(focusHost);
if (focusChild != null) {
if (!dataChanged || isDirectChildHeaderOrFooter(focusChild)
|| focusChild.hasTransientState() || mAdapterHasStableIds) {
// The views won't be changing, so try to maintain
// focus on the current host and virtual view.
accessibilityFocusLayoutRestoreView = focusHost;
accessibilityFocusLayoutRestoreNode = viewRootImpl
.getAccessibilityFocusedVirtualView();
}
// If all else fails, maintain focus at the same
// position.
accessibilityFocusPosition = getPositionForView(focusChild);
}
}
}
View focusLayoutRestoreDirectChild = null;
View focusLayoutRestoreView = null;
// Take focus back to us temporarily to avoid the eventual call to
// clear focus when removing the focused child below from messing
// things up when ViewAncestor assigns focus back to someone else.
final View focusedChild = getFocusedChild();
if (focusedChild != null) {
// TODO: in some cases focusedChild.getParent() == null
// We can remember the focused view to restore after re-layout
// if the data hasn't changed, or if the focused position is a
// header or footer.
if (!dataChanged || isDirectChildHeaderOrFooter(focusedChild)
|| focusedChild.hasTransientState() || mAdapterHasStableIds) {
focusLayoutRestoreDirectChild = focusedChild;
// Remember the specific view that had focus.
focusLayoutRestoreView = findFocus();
if (focusLayoutRestoreView != null) {
// Tell it we are going to mess with it.
focusLayoutRestoreView.onStartTemporaryDetach();
}
}
requestFocus();
}
// Pull all children into the RecycleBin.
// These views will be reused if possible
final int firstPosition = mFirstPosition;
final RecycleBin recycleBin = mRecycler;
// 只有在调用adapter.notifyDatasetChanged()方法一直到layout()布局结束,
// dataChanged为true,默认为false
if (dataChanged) {
// dataChanged为true,说明当前listview是有数据的了,把当前所有的item view
// 存放到RecycleBin对象的mScrapViews中保存
for (int i = 0; i < childCount; i++) {
recycleBin.addScrapView(getChildAt(i), firstPosition+i);
}
} else {
// dataChanged默认为false,第一次执行此方法走这里
recycleBin.fillActiveViews(childCount, firstPosition);
}
// Clear out old views
// 清除当前listview所有的子view
detachAllViewsFromParent();
recycleBin.removeSkippedScrap();
// 在我们调用listview.setAdapter()时候,已经将mLayoutMode = LAYOUT_NORMAL;
// 所以通常情况下可认为mLayoutMode == LAYOUT_NORMAL
switch (mLayoutMode) {
case LAYOUT_SET_SELECTION:
if (newSel != null) {
sel = fillFromSelection(newSel.getTop(), childrenTop, childrenBottom);
} else {
sel = fillFromMiddle(childrenTop, childrenBottom);
}
break;
case LAYOUT_SYNC:
sel = fillSpecific(mSyncPosition, mSpecificTop);
break;
case LAYOUT_FORCE_BOTTOM:
sel = fillUp(mItemCount - 1, childrenBottom);
adjustViewsUpOrDown();
break;
case LAYOUT_FORCE_TOP:
mFirstPosition = 0;
sel = fillFromTop(childrenTop);
adjustViewsUpOrDown();
break;
case LAYOUT_SPECIFIC:
sel = fillSpecific(reconcileSelectedPosition(), mSpecificTop);
break;
case LAYOUT_MOVE_SELECTION:
sel = moveSelection(oldSel, newSel, delta, childrenTop, childrenBottom);
break;
default:
// 通常情况都走这里
if (childCount == 0) {
// listview第一次布局childCount必然为0走这里
if (!mStackFromBottom) {
// 通常我们没有外部调用listview.setStackFromBottom()
// 成员变量mStackFromBottom均为false都走这里
final int position = lookForSelectablePosition(0, true);
setSelectedPositionInt(position);
// 从上到上布局listview能显示得下的子view
sel = fillFromTop(childrenTop);
} else {
final int position = lookForSelectablePosition(mItemCount - 1, false);
setSelectedPositionInt(position);
sel = fillUp(mItemCount - 1, childrenBottom);
}
} else {
// 非第一次layout,之前记录的存在的子view个数childCount不为0
// 包括两种情况:1.listview首次布局中的第二次执行的onlayout();
// 2.在后续listview已经显示存在子view然后数据改变时候调用
// adapter.nitifyDatasetChanged()方法时候
if (mSelectedPosition >= 0 && mSelectedPosition < mItemCount) {
sel = fillSpecific(mSelectedPosition,
oldSel == null ? childrenTop : oldSel.getTop());
} else if (mFirstPosition < mItemCount) {
// 通常情况走这里,fillSpecific()会调用fillUp()和fillDown()布局子view
sel = fillSpecific(mFirstPosition,
oldFirst == null ? childrenTop : oldFirst.getTop());
} else {
sel = fillSpecific(0, childrenTop);
}
}
break;
}
// Flush any cached views that did not get reused above
// 至此,listview已经布局完成能够显示得下的子view,将recycleBin可能剩余的
// mActiveViews中view移动到mScrapViews以便于listview滑动时候复用
recycleBin.scrapActiveViews();
if (sel != null) {
// The current selected item should get focus if items are
// focusable.
if (mItemsCanFocus && hasFocus() && !sel.hasFocus()) {
final boolean focusWasTaken = (sel == focusLayoutRestoreDirectChild &&
focusLayoutRestoreView != null &&
focusLayoutRestoreView.requestFocus()) || sel.requestFocus();
if (!focusWasTaken) {
// Selected item didn't take focus, but we still want to
// make sure something else outside of the selected view
// has focus.
final View focused = getFocusedChild();
if (focused != null) {
focused.clearFocus();
}
positionSelector(INVALID_POSITION, sel);
} else {
sel.setSelected(false);
mSelectorRect.setEmpty();
}
} else {
positionSelector(INVALID_POSITION, sel);
}
mSelectedTop = sel.getTop();
} else {
final boolean inTouchMode = mTouchMode == TOUCH_MODE_TAP
|| mTouchMode == TOUCH_MODE_DONE_WAITING;
if (inTouchMode) {
// If the user's finger is down, select the motion position.
final View child = getChildAt(mMotionPosition - mFirstPosition);
if (child != null) {
positionSelector(mMotionPosition, child);
}
} else if (mSelectorPosition != INVALID_POSITION) {
// If we had previously positioned the selector somewhere,
// put it back there. It might not match up with the data,
// but it's transitioning out so it's not a big deal.
final View child = getChildAt(mSelectorPosition - mFirstPosition);
if (child != null) {
positionSelector(mSelectorPosition, child);
}
} else {
// Otherwise, clear selection.
mSelectedTop = 0;
mSelectorRect.setEmpty();
}
// Even if there is not selected position, we may need to
// restore focus (i.e. something focusable in touch mode).
if (hasFocus() && focusLayoutRestoreView != null) {
focusLayoutRestoreView.requestFocus();
}
}
// Attempt to restore accessibility focus, if necessary.
if (viewRootImpl != null) {
final View newAccessibilityFocusedView = viewRootImpl.getAccessibilityFocusedHost();
if (newAccessibilityFocusedView == null) {
if (accessibilityFocusLayoutRestoreView != null
&& accessibilityFocusLayoutRestoreView.isAttachedToWindow()) {
final AccessibilityNodeProvider provider =
accessibilityFocusLayoutRestoreView.getAccessibilityNodeProvider();
if (accessibilityFocusLayoutRestoreNode != null && provider !=