Android ListView的簡單使用

前言

ListView 是Android的重要控件之一，可以提供多行數據的瀏覽；ListView可以實現複雜的佈局；這邊先從ListView簡單的使用入手；

添加ListView控件

• 在activity_main.xml中添加控件ListView;

<ListView
        android:id="@+id/lv_data_shower"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/rl_title"
        android:layout_marginTop="@dimen/space_10"
        />

• 在MainActivity.java中獲取ListView的實例；

mLVDataShower = (ListView)findViewById(R.id.lv_data_shower);

• 爲ListView添加Adapter；

mAdapter = new DataShowerAdapter(getApplicationContext());
mLVDataShower.setAdapter(mAdapter);

• 爲ListView設置點擊事件監聽；getItem可以從Adapter中獲取一條裏綁定的數據對象，前提是Adapter中覆寫了getItem並返回對象；

mLVDataShower.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                ItemBean itemBean = (ItemBean) mAdapter.getItem(position);
                itemAlert(itemBean);
            }
        });

Adapter的實現

Adapter可以用來給ListView提供數據和佈局；

• 在res->layout 中創建 data_shower_item.xml文件，用來爲ListView每個item提供佈局；這裏只提供兩個TextView；

<?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="match_parent">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="@dimen/list_item_height">

        <TextView
            android:id="@+id/tv_sms"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="@color/colorPrimaryDark"
            android:layout_alignParentRight="true"
            android:layout_centerVertical="true"
            android:textSize="@dimen/text_size_15"
            />

        <TextView
            android:id="@+id/tv_number"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="@color/colorPrimaryDark"
            android:layout_alignParentLeft="true"
            android:layout_centerVertical="true"
            android:textSize="@dimen/text_size_15"
            />
    </RelativeLayout>

</LinearLayout>

• 繼承BaseAdapter,覆寫必須要實現的抽象方法；

public class DataShowerAdapter extends BaseAdapter {

    @Override
    public int getCount() {
        return 0;
    }

    @Override
    public Object getItem(int position) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        return null;
    }
}

• 創建構造方法；將上下文傳入；新建數據庫helper對象，從數據庫中獲取要顯示的數據；獲取LayoutInflater對象，以便稍後獲取佈局對象；

    public DataShowerAdapter(Context context) {
        this.mContext = context;
        this.mItemsDBHelper = new ItemsDBHelper(this.mContext);
        this.mItems = mItemsDBHelper.loadItems();
        this.mInflater = LayoutInflater.from(context);
    }

• 設置ListVeiw要顯示的條數；

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

• 設置每一條在ListView中的位置；

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

• 設置每一條返回的數據對象；

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

• 設置每一條的佈局；DataShowerHolder用來緩存每一條中控件，防止不斷的new造成的卡頓或OOM；

@Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        DataShowerHolder holder;
        if(convertView == null){
            convertView = mInflater.inflate(R.layout.data_shower_item, null);

            holder = new DataShowerHolder();
            holder.tvSms = (TextView)convertView.findViewById(R.id.tv_sms);
            holder.tvNumber = (TextView)convertView.findViewById(R.id.tv_number);

            convertView.setTag(holder);//綁定ViewHolder對象

        } else {
            holder = (DataShowerHolder)convertView.getTag();//取出ViewHolder對象
        }

        holder.tvSms.setText(mItems.get(position).getSms());
        holder.tvNumber.setText(mItems.get(position).getNumber());

        return convertView;
    }

• 創建內部類 DataShowerHolder，用來做ListView 的控件緩存；

    private class DataShowerHolder {
        public TextView tvSms;
        public TextView tvNumber;
    }

• 現在Adapter看起來是這樣子的；

package com.youli.feiyu.fynotification.adapter;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import com.youli.feiyu.fynotification.R;
import com.youli.feiyu.fynotification.bean.ItemBean;
import com.youli.feiyu.fynotification.utility.ItemsDBHelper;

import java.util.ArrayList;

/**
 * Created by Sean on 16/2/23.
 */
public class DataShowerAdapter extends BaseAdapter {

    private Context mContext;
    private LayoutInflater mInflater;
    private ArrayList<ItemBean> mItems;
    private ItemsDBHelper mItemsDBHelper;

    public DataShowerAdapter(Context context) {
        this.mContext = context;
        this.mItemsDBHelper = new ItemsDBHelper(this.mContext);
        this.mItems = mItemsDBHelper.loadItems();
        this.mInflater = LayoutInflater.from(context);
    }

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

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

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

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        DataShowerHolder holder;
        if(convertView == null){
            convertView = mInflater.inflate(R.layout.data_shower_item, null);

            holder = new DataShowerHolder();
            holder.tvSms = (TextView)convertView.findViewById(R.id.tv_sms);
            holder.tvNumber = (TextView)convertView.findViewById(R.id.tv_number);

            convertView.setTag(holder);//綁定ViewHolder對象

        } else {
            holder = (DataShowerHolder)convertView.getTag();//取出ViewHolder對象
        }

        holder.tvSms.setText(mItems.get(position).getSms());
        holder.tvNumber.setText(mItems.get(position).getNumber());

        return convertView;
    }

    private class DataShowerHolder {
        public TextView tvSms;
        public TextView tvNumber;
    }
}

ListView刷新數據

如果後來添加/刪除/修改了一條數據ListView該如何刷新？

• 添加/刪除/修改數據源，然後調用下notifyDataSetChanged；

    public void deleteItem(ItemBean itemBean) {
        mItems.remove(itemBean);
        mItemsDBHelper.deleteItem(itemBean);
        notifyDataSetChanged();
    }

總結

• ListView的顯示 ，需要設置好Adapter；
• Adapter是ListView的數據和佈局來源；
• 在Adapter中要做好控件的緩存，避免卡頓和OOM；
• 調用Adapter的notifyDataSetChanged可以刷新ListView；