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Listview源码分析（1）

2024-11-13 21:50:38   202人阅读

 

首先Listview继承关系：

 

ListView  --extends-->  AbsListview  --extends-->  AdapterView  --extends-->  ViewGroup  --extends-->  View 

 

ListView的构造方法：

 

此时初始化listview的风格，间距

 

  1. public ListView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
    super(context, attrs, defStyleAttr, defStyleRes);
    //TypedArray实例是个属性的容器，context.obtainStyledAttributes()方法返回得到
    final TypedArray a = context.obtainStyledAttributes(
    attrs, com.android.internal.R.styleable.ListView, defStyleAttr, defStyleRes);
    //从属性处初始化值 
    CharSequence[] entries = a.getTextArray(
    com.android.internal.R.styleable.ListView_entries);
    //如果值不为null,shezhi moren de buju fangshi
    if (entries != null) {
    setAdapter(new ArrayAdapter<CharSequence>(context,
    com.android.internal.R.layout.simple_list_item_1, entries));
    }
        //系统自带的风格线
    final Drawable d = a.getDrawable(com.android.internal.R.styleable.ListView_divider);
    if (d != null) {
    // If a divider is specified use its intrinsic height for divider height
    setDivider(d);
    }
        //设置listview头部
    final Drawable osHeader = a.getDrawable(
    com.android.internal.R.styleable.ListView_overScrollHeader);
    if (osHeader != null) {
    setOverscrollHeader(osHeader);
    }
        //设置listview底部
    final Drawable osFooter = a.getDrawable(
    com.android.internal.R.styleable.ListView_overScrollFooter);
    if (osFooter != null) {
    setOverscrollFooter(osFooter);
    }
    //设置listview Item的间距
    final int dividerHeight = a.getDimensionPixelSize(
    com.android.internal.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();
    }
     
在往下看：
 
响应箭头事件时，列表视图可以滚动的最大值. 
  1. public int getMaxScrollAmount() {
    return (int) (MAX_SCROLL_FACTOR * (mBottom - mTop));
    }
     
在往下看：
确保Listview触及顶部或底部边缘 调整在ListView顶部或底部的view以适应我们的视觉感应;
  1. private void adjustViewsUpOrDown() {
    final int childCount = getChildCount();
    int delta;
     
    if (childCount > 0) {
    View child;
     
    if (!mStackFromBottom) {
    // Uh-oh -- we came up short. Slide all views up to make them
    // align with the top
    child = getChildAt(0);
    delta = child.getTop() - mListPadding.top;
    if (mFirstPosition != 0) {
    // It‘s OK to have some space above the first item if it is
    // part of the vertical spacing
    delta -= mDividerHeight;
    }
    if (delta < 0) {
    // We only are looking to see if we are too low, not too high
    delta = 0;
    }
    } else {
    // we are too high, slide all views down to align with bottom
    child = getChildAt(childCount - 1);
    delta = child.getBottom() - (getHeight() - mListPadding.bottom);
     
    if (mFirstPosition + childCount < mItemCount) {
    // It‘s OK to have some space below the last item if it is
    // part of the vertical spacing
    delta += mDividerHeight;
    }
     
    if (delta > 0) {
    delta = 0;
    }
    }
     
    if (delta != 0) {
    offsetChildrenTopAndBottom(-delta);
    }
    }
    }
    接下来是添加头部的方法；为ListView顶部添加一个固定的View，如果HeaderView多于一个，会按照添加的顺序进行排列：
    public void addHeaderView(View v, Object data, boolean isSelectable) {
    final FixedViewInfo info = new FixedViewInfo();
    info.view = v;
    info.data = data;
    info.isSelectable = isSelectable;
    mHeaderViewInfos.add(info);
    mAreAllItemsSelectable &= isSelectable;
     
    // Wrap the adapter if it wasn‘t already wrapped.
    if (mAdapter != null) {
    if (!(mAdapter instanceof HeaderViewListAdapter)) {
    mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, mAdapter);
    }
     
    // In the case of re-adding a header view, or adding one later on,
    // we need to notify the observer.
    if (mDataSetObserver != null) {
    mDataSetObserver.onChanged();
    }
    }
    }
     
接下来 添加 头部view的方法和获取头部view的数目：
  1. public void addHeaderView(View v) {
    addHeaderView(v, null, true);
    }
    @Override
    public int getHeaderViewsCount() {
    return mHeaderViewInfos.size();
    }
     
删除头部的方法；如果头部信息的list>0,并且Adapter不为null，删除头部信息，并进行回调：
  1. public boolean removeHeaderView(View v) {
    //如果头部信息的list>0,并且Adapter不为null，删除头部信息，并进行回调
    if (mHeaderViewInfos.size() > 0) {
    boolean result = false;
    if (mAdapter != null && ((HeaderViewListAdapter) mAdapter).removeHeader(v)) {
    if (mDataSetObserver != null) {
    mDataSetObserver.onChanged();
    }
    result = true;
    }
    //调用下面删除指定view的操作
    removeFixedViewInfo(v, mHeaderViewInfos);
    return result;
    }
    return false;
    }
    这是找到对应的view进行删除操作：
private void removeFixedViewInfo(View v, ArrayList<FixedViewInfo> where) {
int len = where.size();
for (int i = 0; i < len; ++i) {
FixedViewInfo info = where.get(i);
if (info.view == v) {
where.remove(i);
break;
}
}
}
添加Listview底部布局：
/**
* Add a fixed view to appear at the bottom of the list. If addFooterView is
* called more than once, the views will appear in the order they were
* added. Views added using this call can take focus if they want.
* <p>
* NOTE: Call this before calling setAdapter. This is so ListView can wrap
* the supplied cursor with one that will also account for header and footer
* views.
*
* @param v The view to add.
* @param data Data to associate with this view
* @param isSelectable true if the footer view can be selected
*/
public void addFooterView(View v, Object data, boolean isSelectable) {
 
// NOTE: do not enforce the adapter being null here, since unlike in
// addHeaderView, it was never enforced here, and so existing apps are
// relying on being able to add a footer and then calling setAdapter to
// force creation of the HeaderViewListAdapter wrapper
 
FixedViewInfo info = new FixedViewInfo();
info.view = v;
info.data = data;
info.isSelectable = isSelectable;
mFooterViewInfos.add(info);
 
// in the case of re-adding a footer view, or adding one later on,
// we need to notify the observer
if (mAdapter != null && mDataSetObserver != null) {
mDataSetObserver.onChanged();
}
}
 
/**
* Add a fixed view to appear at the bottom of the list. If addFooterView is called more
* than once, the views will appear in the order they were added. Views added using
* this call can take focus if they want.
* <p>NOTE: Call this before calling setAdapter. This is so ListView can wrap the supplied
* cursor with one that will also account for header and footer views.
*
*
* @param v The view to add.
*/
public void addFooterView(View v) {
addFooterView(v, null, true);
}
获取添加的底部布局的个数：
 
@Override
public int getFooterViewsCount() {
return mFooterViewInfos.size();
}
 
删除指定的底部布局，并通知其他相关：
/**
* Removes a previously-added footer view.
*
* @param v The view to remove
* @return
* true if the view was removed, false if the view was not a footer view
*/
public boolean removeFooterView(View v) {
if (mFooterViewInfos.size() > 0) {
boolean result = false;
if (mAdapter != null && ((HeaderViewListAdapter) mAdapter).removeFooter(v)) {
if (mDataSetObserver != null) {
mDataSetObserver.onChanged();
}
result = true;
}
removeFixedViewInfo(v, mFooterViewInfos);
return result;
}
return false;
}
获取listview使用的Adapter:
/**
* Returns the adapter currently in use in this ListView. The returned adapter
* might not be the same adapter passed to {@link #setAdapter(ListAdapter)} but
* might be a {@link WrapperListAdapter}.
*返回listview当前正在使用的Adapter，adapter不一定是通过setAdapter方法传入的adapter，有可能是一个WrapperListAdapter
* @return The adapter currently used to display data in this ListView.
*
* @see #setAdapter(ListAdapter)
*/
@Override
public ListAdapter getAdapter() {
return mAdapter;
}
 
为listview添加数据setAdapter 实现原理：
 
/**
* Sets the data behind this ListView.
*
* The adapter passed to this method may be wrapped by a {@link WrapperListAdapter},
* depending on the ListView features currently in use. For instance, adding
* headers and/or footers will cause the adapter to be wrapped.
* 通过setAdapter方法添加的adapter根据当前ListView的使用情况可能被装饰为一个WrapperListAdapter，比如说添加一个HeaderView或者FooterView。

 

在该方法中，先把以前的数据和观察者去掉，然后再重新设置各种参数

* @param adapter The ListAdapter which is responsible for maintaining the
* data backing this list and for producing a view to represent an
* item in that data set.
*
* @see #getAdapter()
*/
@Override
public void setAdapter(ListAdapter adapter) {
if (mAdapter != null && mDataSetObserver != null) {
mAdapter.unregisterDataSetObserver(mDataSetObserver);
}
//重置list 
resetList();
mRecycler.clear();
 
if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {
mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);
} else {
mAdapter = adapter;
}
 
mOldSelectedPosition = INVALID_POSITION;
mOldSelectedRowId = INVALID_ROW_ID;
 
// AbsListView#setAdapter will update choice mode states.
super.setAdapter(adapter);
 
if (mAdapter != null) {
mAreAllItemsSelectable = mAdapter.areAllItemsEnabled();
mOldItemCount = mItemCount;
mItemCount = mAdapter.getCount();
checkFocus();
 
mDataSetObserver = new AdapterDataSetObserver();
mAdapter.registerDataSetObserver(mDataSetObserver);
 
mRecycler.setViewTypeCount(mAdapter.getViewTypeCount());
 
int position;
if (mStackFromBottom) {
position = lookForSelectablePosition(mItemCount - 1, false);
} else {
position = lookForSelectablePosition(0, true);
}
setSelectedPositionInt(position);
setNextSelectedPositionInt(position);
 
if (mItemCount == 0) {
// Nothing selected
checkSelectionChanged();
}
} else {
mAreAllItemsSelectable = true;
checkFocus();
// Nothing selected
checkSelectionChanged();
}
 
requestLayout();
}
在20行调用了 ，清空listview的头部，也清空底部，删除layout中所有的view：
/**
* The list is empty. Clear everything out.
*
*/
@Override
void resetList() {
// The parent‘s resetList() will remove all views from the layout so we need to
// cleanup the state of our footers and headers
clearRecycledState(mHeaderViewInfos);
clearRecycledState(mFooterViewInfos);
 
super.resetList();
 
mLayoutMode = LAYOUT_NORMAL;
}
8,9行调用clearRecycledState
private void clearRecycledState(ArrayList<FixedViewInfo> infos) { 
if (infos != null) {
final int count = infos.size();
for (int i = 0; i < count; i++) 
{
final View child = infos.get(i).view; final LayoutParams p = (LayoutParams) child.getLayoutParams(); 
if (p != null) { p.recycledHeaderFooter = false;
}
}
}
}
 
 

 

Listview源码分析（1）


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