BaseAdapter分析

今天离职，除了交接，自己时间还是挺多的。

其实 公司对我还是挺好的。自己努力， 希望以后可以做到感恩。

离职后自己还有写事情要做，简单先写一篇blog，记录下。

 

无论好不好，自己先记录下吧。可能以后看现在的文章比较傻逼，当然，如果感觉自己文章傻逼的时候，也就是自己提高的时候。:-)

 

BaseAdapter我们都用得比较多。通常只要实现几个接口 

 

        @Overridepublic int getCount() {// TODO Auto-generated method stubreturn 0;}@Overridepublic Object getItem(int position) {// TODO Auto-generated method stubreturn null;}@Overridepublic long getItemId(int position) {// TODO Auto-generated method stubreturn 0;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {// TODO Auto-generated method stubreturn null;}

 

就可以做对应的实现了，无论是list，还是gridview什么的

 

在看 源码实现之前，首先要了解 适配器模式 和 观察者模式

 

适配器模式， 主要是将各种类型适配，达到比较统一的接口实现。

比如，原来用竹筷子的人，现在只有铁筷子，或者叉子什么的。

或者 head First里面的， 给让火烈鸟 叫，飞 一样。

 

观察者模式， 主要是负责通知，注册，删除，更新，容器中的数据。

让观察者可以容易控制被观察者。

例如java设计模式中的警察抓小偷， 或者head First中的发报纸说明， 猎头说明一样

自己具体的理解，可以见

【观察者的文章】

 

我们看看BaseAdapter的代码

import android.database.DataSetObservable;import android.database.DataSetObserver;import android.view.View;import android.view.ViewGroup;/** * Common base class of common implementation for an {@link Adapter} that can be * used in both {@link ListView} (by implementing the specialized * {@link ListAdapter} interface} and {@link Spinner} (by implementing the * specialized {@link SpinnerAdapter} interface. */public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {    private final DataSetObservable mDataSetObservable = new DataSetObservable();    public boolean hasStableIds() {        return false;    }        public void registerDataSetObserver(DataSetObserver observer) {        mDataSetObservable.registerObserver(observer);    }    public void unregisterDataSetObserver(DataSetObserver observer) {        mDataSetObservable.unregisterObserver(observer);    }        /**     * Notifies the attached View that the underlying data has been changed     * and it should refresh itself.     */    public void notifyDataSetChanged() {        mDataSetObservable.notifyChanged();    }        public void notifyDataSetInvalidated() {        mDataSetObservable.notifyInvalidated();    }    public boolean areAllItemsEnabled() {        return true;    }    public boolean isEnabled(int position) {        return true;    }    public View getDropDownView(int position, View convertView, ViewGroup parent) {        return getView(position, convertView, parent);    }    public int getItemViewType(int position) {        return 0;    }    public int getViewTypeCount() {        return 1;    }        public boolean isEmpty() {        return getCount() == 0;    }}

分别实现了 ListAdapter 和 SpinnerAdapter

public interface ListAdapter extends Adapter {    /**     * Are all items in this ListAdapter enabled?     * If yes it means all items are selectable and clickable.     *      * @return True if all items are enabled     */    public boolean areAllItemsEnabled();    /**     * Returns true if the item at the specified position is not a separator.     * (A separator is a non-selectable, non-clickable item).     *      * The result is unspecified if position is invalid. An {@link ArrayIndexOutOfBoundsException}     * should be thrown in that case for fast failure.     *     * @param position Index of the item     * @return True if the item is not a separator     */    boolean isEnabled(int position);}

 

public interface SpinnerAdapter extends Adapter {    /**     * <p>Get a {@link android.view.View} that displays in the drop down popup     * the data at the specified position in the data set.</p>     *     * @param position      index of the item whose view we want.     * @param convertView   the old view to reuse, if possible. Note: You should     *        check that this view is non-null and of an appropriate type before     *        using. If it is not possible to convert this view to display the     *        correct data, this method can create a new view.     * @param parent the parent that this view will eventually be attached to     * @return a {@link android.view.View} corresponding to the data at the     *         specified position.     */    public View getDropDownView(int position, View convertView, ViewGroup parent);}

分别的实现也很简单

 

    public boolean areAllItemsEnabled() {        return true;    }    public boolean isEnabled(int position) {        return true;    }

 

public View getDropDownView(int position, View convertView, ViewGroup parent) {        return getView(position, convertView, parent);    }

我们再来看看对应的View组件ListView对应setAdapter的代码

 

    public void setAdapter(ListAdapter adapter) {        if (null != mAdapter) {            mAdapter.unregisterDataSetObserver(mDataSetObserver);        }        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;        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();            }            if (mChoiceMode != CHOICE_MODE_NONE &&                    mAdapter.hasStableIds() &&                    mCheckedIdStates == null) {                mCheckedIdStates = new LongSparseArray<Boolean>();            }        } else {            mAreAllItemsSelectable = true;            checkFocus();            // Nothing selected            checkSelectionChanged();        }        if (mCheckStates != null) {            mCheckStates.clear();        }                if (mCheckedIdStates != null) {            mCheckedIdStates.clear();        }        requestLayout();    }

会unregister原来监听的对象，清理对应list的header和footer，

 

 和对应的一些复杂操作。。。