ListView基本用法

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这篇文章是针对Android的ListView的学习笔记。

1 准备布局

一个list_item.xml布局，一个包含list_item.xml的list_view.xml。例：

girl_item.xml
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="horizontal"
              android:layout_width="match_parent"
              android:layout_height="wrap_content">
    <ImageView
        android:id="@+id/girl_image"
        android:src="@drawable/icon1"
        android:layout_width="72dp"
        android:layout_height="72dp"/>

    <TextView
        android:id="@+id/girl_name"
        android:text="chiaki"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginLeft="10dp"/>

</LinearLayout>
list_view.xml
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.luowenqing.a3_6_recycleviewtest.MainActivity">

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

</LinearLayout>

2 自定义适配器

确定数据源类型。例如少女类Girl：

Girl.java
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public class Girl {
    private String name;
    private int imageId;

    public Girl(String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getImageId() {
        return imageId;
    }

    public void setImageId(int imageId) {
        this.imageId = imageId;
    }
}

使用系统提供适配器或自定义适配器类Adapter，类ViewHolder根据需要定义为内部类或外部类，ConvertView,ViewHolder缓存优化。例GirlAdapter：

GirlAdapter.java
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public class GirlAdapter extends ArrayAdapter {

    private int resourceId;

    public GirlAdapter(@NonNull Context context, @LayoutRes int resource, @NonNull List objects) {
        super(context, resource, objects);
        resourceId = resource;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        Girl girl = (Girl) getItem(position);
        View view;
        ViewHolder viewHolder;
        if (convertView == null) {
            view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);

            viewHolder = new ViewHolder();
            viewHolder.girlImage = (ImageView) view.findViewById(R.id.girl_image);
            viewHolder.girlName = (TextView) view.findViewById(R.id.girl_name);
            view.setTag(viewHolder);
        } else {
            view = convertView;
            viewHolder = (ViewHolder) view.getTag();
        }
        viewHolder.girlImage.setImageResource(girl.getImageId());
        viewHolder.girlName.setText(girl.getName());
        return view;
    }

    class ViewHolder {
        ImageView girlImage;
        TextView girlName;
    }
}

3 加载布局

调用类，对应布局list_view.xml；获取数据源传入Adapter中，Adapter类对应list_item.xml。

MainActivity.java
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public class MainActivity extends AppCompatActivity {
    private List<Girl> girlsList = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list_view);

        initGirls();
        
        GirlAdapter girlAdapter = new GirlAdapter(MainActivity.this, R.layout.girl_item, girlsList);

        ListView listView = (ListView) findViewById(R.id.list_view);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Toast.makeText(MainActivity.this, "I love "+girlsList.get(position).getName(),
                        Toast.LENGTH_SHORT).show();
            }
        });
        
        listView.setAdapter(girlAdapter);
    }
    // 准备数据源
    public void initGirls() {
        for (int i = 0 ; i < 3; i++) {
            Girl gir11 = new Girl("chiaki", R.drawable.icon1);
            girlsList.add(gir11);
            Girl gir12 = new Girl("setsuna", R.drawable.icon2);
            girlsList.add(gir12);
            Girl gir13 = new Girl("touma", R.drawable.icon3);
            girlsList.add(gir13);
            Girl gir14 = new Girl("koharu", R.drawable.icon4);
            girlsList.add(gir14);
            Girl gir15 = new Girl("mari", R.drawable.icon5);
            girlsList.add(gir15);
            Girl gir16 = new Girl("nayuki", R.drawable.icon6);
            girlsList.add(gir16);
            Girl gir17 = new Girl("aiko", R.drawable.icon7);
            girlsList.add(gir17);
            Girl gir18 = new Girl("nagisa", R.drawable.icon8);
            girlsList.add(gir18);
        }
    }
}

4 插入 & 删除 & 局部刷新Item

局部更新找到对应更新的item项，如果整个item的子控件都需要更新，调用getView；只需更新某个子控件，可通过findViewById()找出对应控件，进行更新。
先重写list_view.xml布局，重写MainActivity.java模仿数据更新。

list_view.xml
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<?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:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.luowenqing.a3_6_recycleviewtest.MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <EditText
            android:id="@+id/edit_fun"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="3"/>

        <Button
            android:id="@+id/button_fun"
            android:text="function"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"/>
    </LinearLayout>

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

</LinearLayout>
MainActivity
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public class MainActivity extends AppCompatActivity {
    
    private List<Girl> girlsList = new ArrayList<>();
    private ListView listView;
    private Button funButton;
    private EditText funEditText;
    private GirlAdapter girlAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list_view);
        initGirls();
        girlAdapter = new GirlAdapter(MainActivity.this, R.layout.girl_item, girlsList);
        listView = (ListView) findViewById(R.id.list_view);

        funButton = (Button) findViewById(R.id.button_fun);
        funEditText = (EditText) findViewById(R.id.edit_fun);

        funButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String str = funEditText.getText().toString();
                String[] arr = str.split(" ");
                int position = Integer.parseInt(arr[1]);
                switch (arr[0]) {
                    case "delete":
                        girlsList.remove(position);
                        girlAdapter.notifyDataSetChanged();
                        break;
                    case "insert":
                        girlsList.add(position, new Girl("にゃんぱすー"+arr[1], R.drawable.avt));
                        girlAdapter.notifyDataSetChanged();
                        break;
                    case "update":
                        girlsList.set(position, new Girl("にゃんぱすー"+arr[1], R.drawable.avt));
                        updateItem(position);
                        break;
                }
            }
        });

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Toast.makeText(MainActivity.this, "I love "+girlsList.get(position).getName(),
                        Toast.LENGTH_SHORT).show();
            }
        });

        listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {

                return false;
            }
        });
        listView.setAdapter(girlAdapter);
    }

    public void initGirls() {
        for (int i = 0 ; i < 3; i++) {
            Girl gir11 = new Girl("chiaki", R.drawable.icon1);
            girlsList.add(gir11);
            Girl gir12 = new Girl("setsuna", R.drawable.icon2);
            girlsList.add(gir12);
            Girl gir13 = new Girl("touma", R.drawable.icon3);
            girlsList.add(gir13);
            Girl gir14 = new Girl("koharu", R.drawable.icon4);
            girlsList.add(gir14);
            Girl gir15 = new Girl("mari", R.drawable.icon5);
            girlsList.add(gir15);
            Girl gir16 = new Girl("nayuki", R.drawable.icon6);
            girlsList.add(gir16);
            Girl gir17 = new Girl("aiko", R.drawable.icon7);
            girlsList.add(gir17);
            Girl gir18 = new Girl("nagisa", R.drawable.icon8);
            girlsList.add(gir18);
        }
    }

    public void updateItem(int position) {
        int firstVisiblePos = listView.getFirstVisiblePosition();
        int lastVisiblePos = listView.getLastVisiblePosition();
        if (position >= firstVisiblePos && position <= lastVisiblePos) {
            View view = listView.getChildAt(position - firstVisiblePos);
            girlAdapter.getView(position, view, listView);
        }
    }
}

布局的优化，将item的高度设为定值可以减少getView()调用次数。