【Android】之ListView的使用

需求：

在fragment中写入几个listview.，先看下效果图。这里的照片我写的是固定值，可置为不同照片。

1.编写fragment的布局文件fragment_hat，插入标签.（此处MyListView是继承自ListView,稍后说明）

2.编写每个项目的布局文件item_hat.

3.在HatFragment中引入fragment_hat资源文件，贴出OnCreatView方法

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_hat, container, false);
        hats = (MyListView) v.findViewById(R.id.hat_list);
        upload = (Button) v.findViewById(R.id.upload);

        upload.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(getActivity(),UploadActivity.class));
            }
        });
        initData();
        hatsAdapter = new HatsAdapter();
        hats.setAdapter(hatsAdapter);
        hats.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView adapterView, View view, int i, long l) {
                startActivity(new Intent(getActivity(), HatsActivity.class));
            }
        });
        return v;
    }

4.定义一个JavaBeans，记录Hat的各项信息

public class HatBeans {

    private String description;
    private int picture;
    private int state;

    public HatBeans(String description,int state){
        this.description=description;
        this.state=state;
    }

    public HatBeans(String description,int picture,int state){
        this.description=description;
        this.picture=picture;
        this.state=state;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public int getPicture() {
        return picture;
    }

    public void setPicture(int picture) {
        this.picture = picture;
    }

    public int getState(){
        return this.state;
    }

    public void setState(int state){
        this.state=state;
    }
}

5.自定义HatsAdapter,继承BaseAdapter,重写四个方法

public class HatsAdapter extends BaseAdapter {


        @Override
        public int getCount() {
            return hatList.size();
        }

        @Override
        public Object getItem(int i) {
            return hatList.get(i);
        }

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

        @Override
        public View getView(int i, View convertView, ViewGroup viewGroup) {
            HatBeans hatBeans = hatList.get(i);
            View view;
            ViewHolder viewHolder;
            if (convertView == null) {
                view = LayoutInflater.from(getActivity()).inflate(R.layout.item_hat, null);
                viewHolder = new ViewHolder();
                viewHolder.picture = (ImageView) view.findViewById(R.id.hat_pic);
                viewHolder.description = (TextView) view.findViewById(R.id.hat_desc);
                viewHolder.state = (TextView) view.findViewById(R.id.hat_state);
                view.setTag(viewHolder);
            } else {
                view = convertView;
                viewHolder = (ViewHolder) view.getTag();
            }


            viewHolder.picture.setImageResource(R.drawable.pic_launcher);
            viewHolder.description.setText(hatBeans.getDescription());

            int state = hatBeans.getState();
            if (state == HAT_STATE_AUCTIONED)
                viewHolder.state.setText(R.string.state_auctioned);
            else if (state == HAT_STATE_AUCTIONING)
                viewHolder.state.setText(R.string.state_auctioning);
            else if (state == HAT_STATE_SHOW)
                viewHolder.state.setText(R.string.state_show);

            return view;
        }
    }

    class ViewHolder {
        ImageView picture;
        TextView description;
        TextView state;
    }

6.关于ListView，当屏幕不够大时，仅仅ListView部分会发生滚动，这个界面看起来不够完整。我希望得到的效果是，除底部导航栏外所有组件一起滚动。

①可以用ScrollView实现我期待的效果，需要注意的是ScrollView只能直接包含一个组件，我们要将所有参与滚动的组件扔到一个LinearLayout中，并将其的orientation设置为vertical.
②当ScrollView中包含ListView时，我们会遇到一个坑，就是ListView部分只显示一个条目。这时候一个解决办法是重写MyListView继承ListView,，重写OnMeasure方法。注意的是layout和Fragment中保持一致，使用MyListView.

public class MyListView extends ListView{

    public MyListView(Context context) {
        super(context);
    }
    public MyListView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    public MyListView(Context context, AttributeSet attrs,
                                 int defStyle) {
        super(context, attrs, defStyle);
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int expandSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2,
                MeasureSpec.AT_MOST);
        super.onMeasure(widthMeasureSpec, expandSpec);
    }
}

③还有一个问题是，ScrollView会自动定位到第一个ListView条目（显示在顶端）。所以其上部组件被挤到屏幕外，解决这个问题有两种方法，

a.将其上部写入ListView中，设置为固定的部分。

b.在代码中重新设置ScrollView的位置，

scrollView = (ScrollView) findViewById(R.id.scrollView);
scrollView.smoothScrollTo(0, 0);