MVP模式及性能优化

public abstract class BaseActivity<V,P extends BasePresenter<V>>extends AppCompatActivity {
    protected P  mPresenter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mPresenter=createPresenter();
        mPresenter.attachView((V)this);
    }

    /**
     * activity/view会持有presenter层的引用，presenter会引用model层的引用。model加载的数据极有可能是网络数据，且极
     * 有可能是异步子线程加载的数据。加载这样的数据要耗时，一旦用户点击回退推出了当前的view，则view就被释放了，
     * 但是当model层加载数据完成后会回掉监听器,他会拿着view的引用去访问一块已经被释放了的view内存。
     * 这样是没有必要的，是浪费资源的，导致了内存的泄漏。
     */
    @Override
    protected void onDestroy() {
        super.onDestroy();
        mPresenter.detachView();
    }

    public abstract P  createPresenter();
}

public abstract class BasePresenter<V> {

    protected WeakReference<V> mViewRef;//当内存不足时释放内存
    
    public void attachView(V view){
        mViewRef=new WeakReference<V>(view);
    }

    public void detachView(){
        if(mViewRef!=null){
            mViewRef.clear();
            mViewRef=null;
        }
    }

    protected V getView(){
        return mViewRef.get();
    }
}

public class UserActivity extends BaseActivity<UserView,UserPresenter> implements UserView{
    private ListView listview;
    private UserAdapter mAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listview= (ListView) findViewById(R.id.list_view);

        //入口
        mPresenter.fetch();
    }

    @Override
    public UserPresenter createPresenter() {
        return new UserPresenter();
    }

    @Override
    public void showLoading() {
        Toast.makeText(getApplicationContext(),"正在加载...",Toast.LENGTH_LONG).show();
    }

    @Override
    public void showDatas(List<User> datas) {
        mAdapter=new UserAdapter(getApplicationContext(), datas);
        listview.setAdapter(mAdapter);
    }
}

public interface  UserView {

    void showLoading();

    void showDatas(List<User>  datas);
}

public class UserPresenter extends BasePresenter<UserView> {

    UserModel userModel=new UserModelImpl();


    public void fetch(){
        getView().showLoading();
        if(userModel!=null){
            userModel.loadDatas(new UserModel.DataOnLoadingListener() {
                @Override
                public void onComplete(List<User> datas) {
                    getView().showDatas(datas);
                }
            });
        }
    }
}

public interface  UserModel {
    void loadDatas(DataOnLoadingListener listener);

    interface DataOnLoadingListener{
        void onComplete(List<User> datas);
    }
}

public class UserModelImpl implements  UserModel {
    @Override
    public void loadDatas(DataOnLoadingListener listener) {
        List<User> datas= DataUtil.getInstance().getData();

        listener.onComplete(datas);
    }
}

public class UserAdapter extends BaseAdapter {
    private Context context;
    private List<User> datas;

    public UserAdapter(Context context,List<User>datas){
        this.context=context;
        this.datas=datas;
    }
    @Override
    public int getCount() {
        return datas.size();
    }

    @Override
    public Object getItem(int position) {
        return datas.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if(convertView==null){
            convertView=View.inflate(context, R.layout.item, null);
        }
        ViewHolder holder=ViewHolder.getHolder(convertView);
        holder.tv.setText(datas.get(position).getName());
        return convertView;
    }

    static class ViewHolder{
        TextView tv;
        public ViewHolder(View convertView){
            tv=(TextView) convertView.findViewById(R.id.textView);
        }

        public static ViewHolder getHolder(View convertView){
            ViewHolder holder=(ViewHolder) convertView.getTag();
            if(holder==null){
                holder = new ViewHolder(convertView);
                convertView.setTag(holder);
            }
            return holder;
        }
    }

}

public class User {
    private String name;

    public User(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

public class DataUtil {
    private static DataUtil dataUtil=null;

    public static DataUtil getInstance(){
        if(dataUtil==null){
            dataUtil=new DataUtil();
        }
        return dataUtil;
    }

    public List<User> getData(){
        List<User> datas = new ArrayList<>();
        for (int i = 0; i < 20; i++) {
            User user = new User("" + i);
            datas.add(user);
        }
        return datas;
    }

}