深入分析ListView 的缓存机制

private View makeAndAddView(int position, int y, boolean flow, int childrenLeft,
boolean selected) {
View child;//即ChildView

//如果数据没有发生改变
if (!mDataChanged) {
//优先从循环器中获取该位置的视图
// Try to use an existing view for this position
child = mRecycler.getActiveView(position);
if (child != null) {
// Found it -- we're using an existing child
//如果找到了就直接添加到List中
// This just needs to be positioned
setupChild(child, position, y, flow, childrenLeft, selected, true);

return child;
}
}

//如果数据发生了改变，则在该位置上新建一个视图，或者如果可能的话转换一个已经没有用的视图(可能是当整个ListView其他位置发生了变化，但是该位置的ChildView并未发生任何变化)
// Make a new view for this position, or convert an unused view if possible
child = obtainView(position, mIsScrap);

// This needs to be positioned and measured
setupChild(child, position, y, flow, childrenLeft, selected, mIsScrap[0]);

//返回该childView
return child;
}

/**
 * Fill ActiveViews with all of the children of the AbsListView.
 * ... ...
 */
void fillActiveViews(int childCount, int firstActivePosition) {
if (mActiveViews.length < childCount) {
mActiveViews = new View[childCount];
}
mFirstActivePosition = firstActivePosition;

//noinspection MismatchedReadAndWriteOfArray
final View[] activeViews = mActiveViews;
... ...
}

/**
 * Move all views remaining in mActiveViews to mScrapViews.
 */
void scrapActiveViews() {
... ...
//该函数确保mScrapViews的大小不会超过mActiveViews
pruneScrapViews();
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;

    if (convertView == null) {
        convertView = mLayout.inflate(R.layout....);
        holder = new ViewHolder();
        holder.textView = (TextView) convertView
                .findViewById(R.id.textview);
        ... ...
        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }
    holder.textView.setText(mText + position);
    return convertView;
}

/**
 * Responsible for fling behavior. Use {@link #start(int)} to
 * initiate a fling. Each frame of the fling is handled in {@link #run()}.
 * A FlingRunnable will keep re-posting itself until the fling is done.
 *
 */
private class FlingRunnable implements Runnable {
    /**
     * Tracks the decay of a fling scroll
     */
    private final OverScroller mScroller;
    ... ...
}

 /**
* Notifies the attached observers that the underlying data has been changed
* and any View reflecting the data set should refresh itself.
*/
public void notifyDataSetChanged() {
mDataSetObservable.notifyChanged();
}
AdapterView

public interface OnItemLongClickListener {
/**
* Callback method to be invoked when an item in this view has been
* clicked and held.
*... ...
*/
boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id);
}

public interface OnItemClickListener {

    /**
* Callback method to be invoked when an item in this AdapterView has
* been clicked.
*... ...
*/
void onItemClick(AdapterView<?> parent, View view, int position, long id);
}

/**
* Returns the adapter currently associated with this widget.
*... ...
*/
public abstract T getAdapter();
/**
* Sets the adapter that provides the data and the views to represent the data
* in this widget.
*... ...
*/
public abstract void setAdapter(T adapter);

 public boolean performItemClick(View view, int position, long id) {
if (mOnItemClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
if (view != null) {
view.sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
}
mOnItemClickListener.onItemClick(this, view, position, id);
return true;
}
return false;
}

<com.github.mikephil.charting.charts.PieChart
android:id=”@+id/spread_pie_chart”
android:layout_width=”match_parent”
android:layout_height=”320dip” />

ColorTemplate mCt;
mCt = new ColorTemplate();
mCt.addDataSetColors(ColorTemplate.PASTEL_COLORS, this);
mChart = (PieChart) headView.findViewById(R.id.spread_pie_chart);
mChart.setColorTemplate(mCt);
mChart.setDescription(“”);
mChart.setHoleRadius(30f);
mChart.setTransparentCircleRadius(0f);
mChart.setCenterTextSize(18f);
mChart.setDrawXValues(true);
mChart.setUsePercentValues(true);
mChart.setDrawLegend(false);
// space between slices
mChart.setSliceSpace(1f);
mChart.setDrawHoleEnabled(false);
mChart.setTouchEnabled(false);

ArrayList yVals = new ArrayList();
ArrayList xVals = new ArrayList();
for (int i = 0; i < listDatas.size(); i++) {
    yVals.add(new Entry((float)listDatas.get(i).getProvinceCount(), i));
    xVals.add(listDatas.get(i).getProvinceName());
}
DataSet set1 = new DataSet(yVals, "Content");
ArrayList dataSets = new ArrayList();
dataSets.add(set1);
ChartData data = new ChartData(xVals, dataSets);
mChart.setData(data);