安卓开发：ListView（详细）

做一个"Hello World!"入门：

<RelativeLayout 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"
    tools:context=".MainActivity" >
    
    <ListView 
        android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        ></ListView>
</RelativeLayout>

package org.dreamtech.listview;

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends Activity {

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

        ListView lv = (ListView) findViewById(R.id.lv);
        lv.setAdapter(new MyListAdapter());
    }

    // listview的数据适配器
    private class MyListAdapter extends BaseAdapter {

        @Override
        public int getCount() {
            // 一共有多少条数据需要显示
            return 6;
        }

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

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

        // 显示
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            TextView tv = new TextView(MainActivity.this);
            tv.setText("haha" + position);
            return tv;
        }

    }

}

 

即可显示一个最基本的listview

 

不过存在一个问题：如果总条目过多的时候，快速滑动滚动条，那么会内存溢出，奔溃

优化写法（实际开发中采用）：

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            TextView tv;
            if (convertView == null) {
                tv = new TextView(MainActivity.this);
            } else {
                tv = (TextView) convertView;
            }
            tv.setText("HELLO"+position);
            return tv;
        }

 

ListView显示数据原理：MVC

 

布局方面注意一个细节：避免将高写成wrap

比如：

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

正确写法：

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

 

原因："高"如果是包裹内容(wrap)，无法计算出要显示多少条目，所以每次显示一个新的条目都需要尝试取校验，是否可以显示出来

 

接下来做复杂的页面：复杂页面通常需要"打气筒"

package org.dreamtech.listview;

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView lv = (ListView) findViewById(R.id.lv);
        lv.setAdapter(new MyAdapter());
    }

    private class MyAdapter extends BaseAdapter {

        @Override
        public int getCount() {
            return 7;
        }

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

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

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View view;
            if (convertView == null) {
                view = View.inflate(getApplicationContext(), R.layout.item,
                        null);
            } else {
                view = convertView;
            }
            return view;
        }

    }
}

 

新写一个布局（layout）item.xml：

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

    <ImageView
        android:id="@+id/iv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher" />

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/iv"
        android:singleLine="true"
        android:ellipsize="end"
        android:textColor="#000000"
        android:textSize="20sp"
        android:layout_marginTop="3dp"
        android:text="安卓开发示例(title)" />
    <TextView
        android:id="@+id/tv_message"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/iv"
        android:layout_below="@id/tv_title"
        android:singleLine="true"
        android:ellipsize="end"
        android:textColor="#999999"
        android:textSize="15sp"
        android:text="安卓开发示例(message)" />
</RelativeLayout>

 

好的看下效果：

 

获取打气筒的方式：上边是第一种（通常）

第二种：

            LayoutInflater.from(getApplicationContext()).inflate(resource, root)

第三种：

                LayoutInflater inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
                inflater.inflate(resource, root);

 

还有方法，常用的只有这三种

 

 

数组适配器：

一个简单的布局：item.xml:

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="TextView"
    android:textAppearance="?android:attr/textAppearanceLarge" />

package org.dreamtech.arrayadapter;

import android.os.Bundle;
import android.app.Activity;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends Activity {

    String objects[] = { "a", "b", "c", "d", "e", "f" };

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

        ListView lv = (ListView) findViewById(R.id.lv);

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                R.layout.item, objects);

        lv.setAdapter(adapter);
    }

}

 

效果：

 

 

simpleadapter:

 

package org.dreamtech.simpleadapter;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.os.Bundle;
import android.app.Activity;
import android.widget.ListView;
import android.widget.SimpleAdapter;

public class MainActivity extends Activity {

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

        ListView lv = (ListView) findViewById(R.id.lv);
        // [1.1]准备listview 要显示的数据
        List<Map<String, String>> data = new ArrayList<Map<String, String>>();
        Map<String, String> map1 = new HashMap<String, String>();
        map1.put("name", "张飞");
        map1.put("tel", "1388888");

        Map<String, String> map2 = new HashMap<String, String>();
        map2.put("name", "赵云");
        map2.put("tel", "110");

        Map<String, String> map3 = new HashMap<String, String>();
        map3.put("name", "貂蝉");
        map3.put("tel", "13882223");

        Map<String, String> map4 = new HashMap<String, String>();
        map4.put("name", "关羽");
        map4.put("tel", "119");

        // [1.1]把map加入到集合中
        data.add(map1);
        data.add(map2);
        data.add(map3);
        data.add(map4);

        // [2]设置数据适配器 resource 我们定义的布局文件
        // from map集合的键
        SimpleAdapter adapter = new SimpleAdapter(getApplicationContext(),
                data, R.layout.item, new String[] { "name", "tel" },
                new int[] { R.id.tv_name, R.id.tv_tel });

        // [3]设置数据适配器
        lv.setAdapter(adapter);
    }
}

 

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="match_parent"
    android:orientation="horizontal" >

    <TextView
        android:id="@+id/tv_name"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="20sp" />

    <TextView
        android:id="@+id/tv_tel"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textColor="#ff0000"
        android:textSize="20sp" />

</LinearLayout>

 

 

 

 

 

最后：把数据库里面的数据展示在ListView上：

这里创建了数据库：http://www.cnblogs.com/xuyiqing/p/8868681.html

代码：

package org.dreamtech.sqlite;

import java.util.ArrayList;
import java.util.List;

import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class MainActivity extends Activity {

    private MyOpenHelper myOpenHelper;
    private List<Person> lists;
    private ListView lv;

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

        lv = (ListView) findViewById(R.id.lv);

        lists = new ArrayList<Person>();

        myOpenHelper = new MyOpenHelper(getApplicationContext());
    }

    // 增
    public void click1(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", "zhangsan");
        values.put("tel", "110");
        // 返回新行的id
        long insert = db.insert("info", null, values);
        db.close();
        if (insert > 0) {
            Toast.makeText(getApplicationContext(), "add 成功", Toast.LENGTH_LONG)
                    .show();
        } else {
            Toast.makeText(getApplicationContext(), "add 失败", Toast.LENGTH_LONG)
                    .show();
        }
    }

    // 删
    public void click2(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        // 返回值：影响的行数
        int delete = db.delete("info", "name=?", new String[] { "zhangsan" });
        db.close();
        Toast.makeText(getApplicationContext(), "删除了" + delete + "行",
                Toast.LENGTH_LONG).show();
    }

    // 改
    public void click3(View v) {
        SQLiteDatabase db = myOpenHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("tel", "666");
        // 返回值：更新了多少行
        int update = db.update("info", values, "name=?",
                new String[] { "zhangsan" });
        db.close();
        Toast.makeText(getApplicationContext(), "更新了" + update + "行",
                Toast.LENGTH_LONG).show();
    }

    // 查
    public void click4(View v) {

        SQLiteDatabase db = myOpenHelper.getWritableDatabase();

        Cursor cursor = db.query("info", null, null, null, null, null, null);

        if (cursor != null && cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                String name = cursor.getString(1);
                String phone = cursor.getString(2);

                // 封装到javabean
                Person person = new Person();
                person.setName(name);
                person.setPhone(phone);
                lists.add(person);
            }
            lv.setAdapter(new MyAdapter());
        }
    }

    private class MyAdapter extends BaseAdapter {

        @Override
        public int getCount() {
            return 10;
        }

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

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

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View view;
            if (convertView == null) {
                view = View.inflate(getApplicationContext(), R.layout.item,
                        null);
            } else {
                view = convertView;
            }

            TextView tv_name = (TextView) view.findViewById(R.id.tv_name);
            TextView tv_phone = (TextView) view.findViewById(R.id.tv_name);

            Person person = lists.get(position);
            tv_name.setText(person.getName());
            tv_phone.setText(person.getPhone());
            return view;
        }

    }
}

<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"
    tools:context=".MainActivity" >

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click1"
        android:text="add" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click2"
        android:text="delete" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click3"
        android:text="update" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click4"
        android:text="find" />
    
    
    <ListView 
        android:id="@+id/lv"
         android:layout_width="match_parent"
        android:layout_height="match_parent"
        ></ListView>
    

</LinearLayout>

package org.dreamtech.sqlite;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class MyOpenHelper extends SQLiteOpenHelper {

    public MyOpenHelper(Context context) {
        super(context, "dreamtech.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table info(_id integer primary key autoincrement,name varchar(20),tel varchar(20))");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {    
    }

}

<?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"
    android:orientation="horizontal" >

    <TextView
        android:id="@+id/tv_name"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="agagag"
        android:textSize="20sp"
        android:layout_weight="1" />

    <TextView
        android:id="@+id/tv_phone"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="agagag"
         android:textSize="20sp"
         android:textColor="#ff0000"
        android:layout_weight="1" />

</LinearLayout>