ListView常用小技巧

ListView在我们Android项目中的地位是有目共睹的，相信几乎每一个App中都有它的身影。
ListView主要是用列表形式来加载数据，在特定情况下需要实现一些特殊功能：如刷新数据，加载数据，实现动画效果等。
作为我们常用的控件，有哪些需要注意的呢？

**为ListView的每一Item设置分隔线

第一种方法：也是最简单地方法，在布局文件中设置ListView的
divider属性
如：android:divider=”@color/black”
第二种方法：设置android:divider=”@null”表示不要分隔线，然后，自己在Item布局中添加分隔线。

 <ListView  android:id="@+id/test_lv" android:layout_width="match_parent" android:layout_height="wrap_content" android:divider="#d1d1d1"<!--设置分隔线颜色-->
        android:dividerHeight="1px"<!--设置分隔线高度-->
        >
 </ListView>

** 默认情况下，ListView的item有点击效果，怎么样改变这种效果呢？
设置ListViewr的android:listSelector属性，比如可以设置透明取消这种效果android:listSelector=”@android:color/transparent”
也可以设置自己想要的效果，添加对应的color资源或drawble资源 就可以了。
** 当数据比较多的时候，ListView在滚动时候会显示一个默认的滚动条，要取消这个滚动条的话，可以设置android:scrollbars属性
如：android:scrollbars=”none”
** ListView性能优化，必用ViewHolder来充分发挥ListView的recycle机制
** ListView中数据动态变化，添加或删除数据操作，效果显而易见。

//实现ListView数据添加删除
public class MainActivity extends Activity implements View.OnClickListener {
    private ListView test_lv;
    private List<TestBean> dataList;
    private TestAdapter adapter;
    private Button add_btn, del_btn;
    private ImageView emptyIv;
    private LinearLayout operator_ll;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initDatas();
        initViews();

    }

    private void initDatas() {
        dataList = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            TestBean bean = new TestBean();
            bean.setTitle("标题_" + i);
            bean.setContent("这是内容_" + i);
            bean.setType(i % 2 == 0 ? 1 : 2);
            dataList.add(bean);
        }
    }

    private void initViews() {
        this.test_lv = (ListView) findViewById(R.id.test_lv);
        this.add_btn = (Button) findViewById(R.id.add_btn);
        this.del_btn = (Button) findViewById(R.id.del_btn);
        emptyIv = (ImageView) findViewById(R.id.empty_iv);
        operator_ll=(LinearLayout)findViewById(R.id.operator_ll);
        this.add_btn.setOnClickListener(this);
        this.del_btn.setOnClickListener(this);
        if (dataList.size() == 0) {
            emptyIv.setVisibility(View.VISIBLE);
            operator_ll.setVisibility(View.GONE);
            test_lv.setEmptyView(emptyIv);
        } else {
            emptyIv.setVisibility(View.GONE);
            operator_ll.setVisibility(View.VISIBLE);
            adapter = new TestAdapter(this, dataList);
            test_lv.setAdapter(adapter);
        }
        test_lv.setSelection(15);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.add_btn:
                //默认增加在第一个位置
                TestBean bean = new TestBean();
                bean.setTitle("增加项");
                bean.setContent("这是增加内容");
                bean.setType(1);
                dataList.add(0, bean);
                break;
            case R.id.del_btn:
                //默认删除第一条数据
                dataList.remove(0);
                break;
        }
        adapter.notifyDataSetChanged();//刷新ListView数据
    }
}
//ListView对应Adapter
public class TestAdapter extends BaseAdapter {
    private Context mContext;
    private List<TestBean> listDatas;

    public TestAdapter(Context mContext, List<TestBean> listDatas) {
        this.mContext = mContext;
        this.listDatas = listDatas;
    }

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

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

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        if (convertView == null) {
            holder = new ViewHolder();
            convertView = LayoutInflater.from(mContext).inflate(R.layout.test_item, null);
            holder.title = (TextView) convertView.findViewById(R.id.item_title);
            holder.content = (TextView) convertView.findViewById(R.id.item_content);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        holder.content.setText(listDatas.get(position).getContent());
        holder.title.setText(listDatas.get(position).getTitle());
        return convertView;
    }

    final class ViewHolder {
        TextView title;
        TextView content;
    }
}

** 类似聊天界面，ListView中有多种item样式效果

//实现ListView中多种item样式
public class TypeActivity extends Activity {
    private ListView type_lv;
    private List<TestBean> dataList;
    private TypeAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_type);
        initDatas();
        initViews();

    }

    private void initDatas() {
        dataList = new ArrayList<>();
        for (int i = 0; i < 9; i++) {
            TestBean bean = new TestBean();
            bean.setTitle("标题_" + i);
            bean.setContent("这是内容_" + i);
            bean.setType(i % 2 == 0 ? 1 : 2);
            dataList.add(bean);
        }
    }

    private void initViews() {
        this.type_lv = (ListView) findViewById(R.id.type_lv);
        adapter = new TypeAdapter(this, dataList);
        type_lv.setAdapter(adapter);

    }
}
//对应Adapter
public class TypeAdapter extends BaseAdapter {
    private Context mContext;
    private List<TestBean> listDatas;

    public TypeAdapter(Context mContext, List<TestBean> listDatas) {
        this.mContext = mContext;
        this.listDatas = listDatas;
    }

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

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

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        //根据样式设置不同的布局及数据展示
        int type = getItemViewType(position);
        if (convertView == null) {
            holder = new ViewHolder();
            if (type == 1) {
                convertView = LayoutInflater.from(mContext).inflate(R.layout.test_item, null);
                holder.title = (TextView) convertView.findViewById(R.id.item_title);
                holder.content = (TextView) convertView.findViewById(R.id.item_content);
            } else {
                convertView = LayoutInflater.from(mContext).inflate(R.layout.type_item, null);
                holder.title = (TextView) convertView.findViewById(R.id.type_title);
                holder.content = (TextView) convertView.findViewById(R.id.type_title);
            }
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        holder.content.setText(listDatas.get(position).getContent());
        holder.title.setText(listDatas.get(position).getTitle());
        return convertView;
    }
//关键方法之getViewTypeCount：获取有多少种样式
    @Override
    public int getViewTypeCount() {
        return 2;
    }
//关键方法之getItemViewType：获取item类型
    @Override
    public int getItemViewType(int position) {
        return listDatas.get(position).getType();
    }

    final class ViewHolder {
        TextView title;
        TextView content;
    }
}

相关布局
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical">

    <LinearLayout  android:id="@+id/operator_ll" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal">

        <Button  android:id="@+id/add_btn" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:gravity="center" android:text="添加" />

        <Button  android:id="@+id/del_btn" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:gravity="center" android:text="删除" />
    </LinearLayout>

    <ListView  android:id="@+id/test_lv" android:layout_width="match_parent" android:layout_height="wrap_content" android:divider="#d1d1d1"<!--分隔线颜色-->
        android:dividerHeight="1px"<!--分隔线高度-->
        android:listSelector="@android:color/transparent"<!--取消默认点击效果-->
        android:scrollbars="none"><!--隐藏滚动条-->
        </ListView>

    <ImageView  android:id="@+id/empty_iv" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center" android:layout_marginTop="100dp" android:src="@mipmap/empty" android:visibility="gone" />

</LinearLayout>

activity_type.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical">


    <ListView  android:id="@+id/type_lv" android:layout_width="match_parent" android:layout_height="wrap_content" ></ListView>


</LinearLayout>

test_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical" android:paddingLeft="15dp" android:layout_marginTop="5dp" android:layout_marginBottom="5dp">

    <TextView  android:id="@+id/item_title" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello World!" />

    <TextView  android:id="@+id/item_content" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="5dp" android:text="Hello World!" />
</LinearLayout>

type_item.xml: