Listview源码分析（1）

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;

}

}

}

}