ListView的使用（二）_extends baseadapte public list<string> (int i) { r-优快云博客

本文链接：https://blog.youkuaiyun.com/litengit/article/details/51154119

上一节说了ListView使用Android API 提供了的Adapter，下面我们自己自定义一个Adapter。一般我们都要继承BaseAdapter来实现自定义。BaseAdapter是以抽象类，我只需要实现其中的几个方法就OK。

准备数据
创建自定义的Adapter 类，并且继承BaseAdapter
构建适配器
把适配器添加到ListView，并显示。

首先准备数据：

创建一个对象：

public class User {
    public String name;
    public String email;
    public String address;
}

创建集合数据：

private List<User> mUsers;
private void prepareUserList() {
    mUsers = new ArrayList<>();
    for (int i = 0; i < 15; i++) {
        User user = new User();
        user.name = "User Name " + i;
        user.email = "litengit@16" + i + ".com";
        user.address = "火星" + i + "号";
        mUsers.add(user);
    }
}

然后自定义Adapter：

public class UserListAdapter extends BaseAdapter {

    private List<User> mUsers = null;
    private LayoutInflater mInflater = null;

    public UserListAdapter(Context context, List<User> users) {
        mInflater = LayoutInflater.from(context);
        mUsers = users;
    }

    @Override
    public int getCount() { // ListView 的行数
        return mUsers == null ? 0 : mUsers.size();
    }

    @Override
    public Object getItem(int position) { // ListView 每一行的数据
        return mUsers == null ? null : mUsers.get(position);
    }

    @Override
    public long getItemId(int position) {// ListView每一行的Id
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        if (convertView == null) { // 对getView进行优化，利用缓存的item，减少不必要的View的创建
            convertView = mInflater.inflate(R.layout.item_2, parent, false);
            holder = new ViewHolder(convertView);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        //填充每一行的数据
        User user = mUsers.get(position);
        holder.mTvName.setText(user.name);
        holder.mTvEmail.setText(user.email);
        holder.mTvAddress.setText(user.address);
        return convertView;
    }

    /**
     * 创建一个实体类，用来装每一行的控件,这样我们可以很容易的通过对象调用它们。
     */
    private static class ViewHolder {
        public TextView mTvName;
        public TextView mTvEmail;
        public TextView mTvAddress;

        public ViewHolder(View convertView) {
            mTvName = (TextView) convertView.findViewById(R.id.tvName);
            mTvEmail = (TextView) convertView.findViewById(R.id.tvEmail);
            mTvAddress = (TextView) convertView.findViewById(R.id.tvAddress);
        }
    }
}

构建适配器

UserListAdapter adapter = new UserListAdapter(this,mUsers);

把适配器添加到ListView，并显示。

mListView.setAdapter(adapter);

ListView 多布局

ListView 多布局，就是ListView显示多种View，不再想之前每一行都显示一样的View。我们可以通过BaseAdapter的getItemViewType和getViewTypeCount来实现。

getItemViewType:返回布局类型有哪几个类型。类型为int型，且必须从0开始。

getViewTypeCount：返回布局类型数量。

我们可以根据布局的类型在getView()里做具体的数据填充。

首先我们准备一下数据,包含一个接口Entity,一个分组类Group，一个用户类User:

接口Entity:

public  interface Entity {}

分组类Group:

public class Group implements Entity {
    public String name;
    public String groupId;
}

用户类User:

public class User implements Entity {
    public String name;
    public String email;
    public String address;
}

准备List集合数据：

private List<Entity> mEntities = null;

private void prepareUserGroupList() {
    mEntities = new ArrayList<>();
    for (int i = 0; i < 20; i++) {
        Entity entity = null;
        if (i % 2 == 0) {
            entity = new Group();
            ((Group) entity).name = "分组 " + i;
            ((Group) entity).groupId = "" + i;
        } else {
            entity = new User();
            ((User) entity).name = "User Name " + i;
            ((User) entity).email = "litengit@16" + i + ".com";
            ((User) entity).address = "火星" + i + "号";
        }

        mEntities.add(entity);
    }
}

准备布局：

分组布局：

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

    <TextView
        android:padding="10dp"
        android:textColor="@color/colorPrimary"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tvGroupName" />
</LinearLayout>

用户布局：

<?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="10dp">

    <TextView
        android:id="@+id/tvName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="5dp"
        android:paddingTop="5dp"
        android:text="name"
        android:textSize="18sp" />

    <TextView
        android:id="@+id/tvEmail"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="5dp"
        android:paddingTop="5dp"
        android:text="email"
        android:textSize="18sp" />

    <TextView
        android:id="@+id/tvAddress"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="5dp"
        android:paddingTop="5dp"
        android:text="address"
        android:textSize="18sp" />
</LinearLayout>

自定义Adapter：

public class UserGroupListAdapter extends BaseAdapter {
    private final int COUNT = 2;

    private final int TYPE_GROUP = 0;
    private final int TYPE_USER = 1;

    private List<Entity> mEntities;
    private LayoutInflater mInflater;

    public UserGroupListAdapter(Context context, List<Entity> entities) {
        mEntities = entities;
        mInflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() { // ListView 的行数
        return mEntities == null ? 0 : mEntities.size();
    }

    @Override
    public Object getItem(int position) { // ListView 每一行的数据
        return mEntities == null ? null : mEntities.get(position);
    }

    @Override
    public long getItemId(int position) {// ListView每一行的Id
        return position;
    }

    @Override
    public int getItemViewType(int position) {
        int type = TYPE_GROUP;
        Entity entity = mEntities.get(position);
        if (entity instanceof Group) {
            type = TYPE_GROUP;
        } else if (entity instanceof User) {
            type = TYPE_USER;
        }
        return type;
    }

    @Override
    public int getViewTypeCount() {
        return COUNT;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        int type = getItemViewType(position);
        if (convertView == null) { // 对getView进行优化，利用缓存的item，减少不必要的View的创建
            switch (type) {
                case TYPE_GROUP:
                    convertView = mInflater.inflate(R.layout.group_item, parent, false);
                    holder = new GroupHolder(convertView);
                    convertView.setTag(holder);
                    break;
                case TYPE_USER:
                    convertView = mInflater.inflate(R.layout.item_2, parent, false);
                    holder = new UserHolder(convertView);
                    convertView.setTag(holder);
                    break;
                default:
                    break;
            }
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        if (holder instanceof GroupHolder) {
            Group group = (Group) mEntities.get(position);
            ((GroupHolder) holder).tvGroupName.setText(group.name);
        }else if (holder instanceof UserHolder) {
            User user = (User) mEntities.get(position);
            ((UserHolder) holder).mTvName.setText(user.name);
            ((UserHolder) holder).mTvEmail.setText(user.email);
            ((UserHolder) holder).mTvAddress.setText(user.address);
        }
        return convertView;
    }

    public static class ViewHolder{
    }

    /**
     * 分组布局的ViewHolder
     */
    public static class GroupHolder extends ViewHolder{
        public TextView tvGroupName;

        public GroupHolder(View convertView) {
            this.tvGroupName = (TextView) convertView.findViewById(R.id.tvGroupName);
        }
    }

    /**
     * 用户布局的ViewHolder
     */
    public static class UserHolder extends ViewHolder{
        public TextView mTvName;
        public TextView mTvEmail;
        public TextView mTvAddress;

        public UserHolder(View convertView) {
            mTvName = (TextView) convertView.findViewById(R.id.tvName);
            mTvEmail = (TextView) convertView.findViewById(R.id.tvEmail);
            mTvAddress = (TextView) convertView.findViewById(R.id.tvAddress);
        }
    }
}

构建Adapter并显示：

UserGroupListAdapter adapter = new UserGroupListAdapter(this, mEntities);
mListView.setAdapter(adapter);

我们看效果：
在这里插入图片描述