ArrayAdapter

Android Adapter:ArrayAdapter篇

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源码：AndroidDemo/Notification
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这是Android Adapter系列文章的第一篇，该系列主要会讲到如下几种Adapter。

ArrayAdapter是BaseAdapter的一个具体实现，可直接使用泛型进行构造，能像List一样直接对Adapter进行增删操作。

ArrayAdapter的构造函数

ArrayAdapter共有6个构造函数，前5种都是调用最后一个构造函数：

public ArrayAdapter(@NonNull Context context, @LayoutRes int resource)

public ArrayAdapter(@NonNull Context context, @LayoutRes int resource,
            @IdRes int textViewResourceId)
            
public ArrayAdapter(@NonNull Context context, @LayoutRes int resource, @NonNull T[] objects)

public ArrayAdapter(@NonNull Context context, @LayoutRes int resource,
            @IdRes int textViewResourceId, @NonNull T[] objects)
            
public ArrayAdapter(@NonNull Context context, @LayoutRes int resource,
            @NonNull List<T> objects)
            
public ArrayAdapter(@NonNull Context context, @LayoutRes int resource,
            @IdRes int textViewResourceId, @NonNull List<T> objects)

ArrayAdapter特性

默认情况下，ArrayAdapter期望布局文件里只有一个TextView，连Layout都不能包含（构造方法1、3、5）。如果你想使用复杂的布局，则你必须向构造函数传递一个field id，即布局中对应TextView的id。如果想实现更复杂的布局，那么你就得重写BaseAdapter的getView(int, View, ViewGroup)方法返回你需要的View。这就是实现泛型操作带有List功能的Adapter了。

ArrayAdapter会调用List中对象的toString()方法，所以可以通过重写Object的toString()方法来控制TextView的显示。

其实，以上特性查看ArrayAdapter的源码就可以看出来了。ArrayAdapter的getView(int, View, ViewGroup)方法最终调用了createViewFromResource(inflater, position, convertView, parent, resource)方法，源码如下：

private @NonNull View createViewFromResource(@NonNull LayoutInflater inflater, int position, @Nullable View convertView, @NonNull ViewGroup parent, int resource) {
   final View view;
   final TextView text;

   if (convertView == null) {
       view = inflater.inflate(resource, parent, false);
   } else {
       view = convertView;
   }

   try {
       //mFieldId即为构造函数中的textViewResourceId
       if (mFieldId == 0) {
           //  If no custom field is assigned, assume the whole resource is a TextView
           text = (TextView) view;
       } else {
           //  Otherwise, find the TextView field within the layout
           text = (TextView) view.findViewById(mFieldId);

           if (text == null) {
               throw new RuntimeException("Failed to find view with ID "
                       + mContext.getResources().getResourceName(mFieldId)
                       + " in item layout");
           }
       }
   } catch (ClassCastException e) {
       Log.e("ArrayAdapter", "You must supply a resource ID for a TextView");
       throw new IllegalStateException(
               "ArrayAdapter requires the resource ID to be a TextView", e);
   }

   final T item = getItem(position);
   if (item instanceof CharSequence) {
       text.setText((CharSequence) item);
   } else {
       //如果想控制ArrayAdapter显示，复写toString()即可
       text.setText(item.toString());
   }

   return view;
}

ArrayAdapter的List特性

ArrayAdapter中的数组操作方法可以总结如下，其都是通过对构造函数或者后期添加的List数据进行增删操作来实现的，具体可以参看源码。

//添加一个对象到ArrayAdapter
void add(T object);

//将数组全部添加到ArrayAdapter
void addAll(@NonNull Collection<? extends T> collection);

//将数组全部添加到ArrayAdapter
void addAll(T ... items);

//插入新条目到指定位置
void insert(@Nullable T object, int index);

//清除所有元素
void clear()；

//移出一条从数组，这里并没有指定位置
void remove(T object)；

//控制当执行add(T), insert(T, int), remove(T), clear()等的操作时，是否自动执行`notifyDataSetChanged()`自动刷新UI。当其为false时，需要手动调用`notifyDataSetChanged()`方法
void setNotifyOnChange(boolean notifyOnChange);

//对ArrayAdapter显示的数据进行排序
void sort(Comparator<? super T> comparator);

Demo时间

ArrayAdapter的实现原理讲的差不多了，那么接下来就是demo时间了。

ArrayAdapter的最简单使用

ArrayAdapter的最简单使用应该就属构造函数1、3、5，一赤裸裸的Textview布局，一数组足矣。
代码真心简单的不要不要的，如果想尝试自定义简单ArrayAdapter的布局可以参考custom_simplest_list_item.xml

SimplestArrayAdapterActivity.java:

public class SimplestArrayAdapterActivity extends Activity {

    private ListView mLv;

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

        mLv = (ListView) findViewById(R.id.lv);
        mLv.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, Util.generateString(10)));
        //此处为自定义的simple_list_item
        //mLv.setAdapter(new ArrayAdapter<String>(this, R.layout.custom_simplest_list_item, Util.generateString(10)));
    }
}

activity_simplest_array_adapter.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"
    tools:context=".SimplestArrayAdapterActivity">

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

</LinearLayout>

custom_simplest_list_item.xml:

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

</TextView>

ArrayAdapter的进阶使用

ArrayAdapter的进阶使用其实不比上面的demo难多少，只是这里调用的构造函数2、4、6中的一种，只需要自定义一个包含TextView的布局，将布局id和TextView的id传递给ArrayAdapter即可。

//替换此处
mLv.setAdapter(new ArrayAdapter<String>(this,R.layout.custom_list_item,R.id.tv_i_am_textview, Util.generateString(10)));

custom_list_item.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="horizontal"
    tools:context="com.littlejie.adapter.MiddleArrayAdapterActivity">

    <ImageView
        android:layout_width="30dp"
        android:layout_height="30dp"
        android:src="@mipmap/ic_launcher" />

    <TextView
        android:id="@+id/tv_i_am_textview"
        android:layout_width="match_parent"
        android:layout_height="30dp"
        android:gravity="center" />
</LinearLayout>

运行结果如下：

ArrayAdapter的超阶使用

ArrayAdapter实现复杂布局其实也很简单，只需要重写getView(int, View, ViewGroup)方法即可，其余和前两个例子没啥区别。getView(int, View, ViewGroup)后面讲BaseAdapter的时候会详细讲。

HardestArrayAdapterActivity.java:

public class HardestArrayAdapterActivity extends Activity {

    private ListView mLv;

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

        mLv = (ListView) findViewById(R.id.lv);
        mLv.setAdapter(new MyArrayAdapter(this, generateData(10)));
    }

    private List<Student> generateData(int num) {
        List<Student> students = new ArrayList<>();
        for (int i = 0; i < num; i++) {
            Student student = new Student();
            student.setName("学生 " + i);
            student.setGender(i % 2 == 0 ? "男" : "女");
            student.setScore(String.valueOf(100 - i));
            students.add(student);
        }
        return students;
    }

    /**
     * 自定义ArrayAdapter,重写getView(int, View, ViewGroup)方法
     */
    private class MyArrayAdapter extends ArrayAdapter<Student> {

        private List<Student> mStudents;

        public MyArrayAdapter(Context context, List<Student> objects) {
            super(context, 0, objects);
            mStudents = objects;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.custom_hardest_list_item, null);
            TextView tvName = (TextView) convertView.findViewById(R.id.tv_name);
            TextView tvGender = (TextView) convertView.findViewById(R.id.tv_gender);
            TextView tvScore = (TextView) convertView.findViewById(R.id.tv_score);

            Student student = mStudents.get(position);
            tvName.setText("姓名:" + student.getName());
            tvGender.setText("性别:" + student.getGender());
            tvScore.setText("成绩:" + student.getScore());
            return convertView;
        }
    }

    /**
     * 定义学生对象,存放姓名、性别、成绩
     */
    private class Student {
        private String name;
        private String gender;
        private String score;

        public String getName() {
            return name;
        }

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

        public String getGender() {
            return gender;
        }

        public void setGender(String gender) {
            this.gender = gender;
        }

        public String getScore() {
            return score;
        }

        public void setScore(String score) {
            this.score = score;
        }

        @Override
        public String toString() {
            return "姓名:" + name + "\n性别:" + gender + "\n成绩:" + score;
        }
    }
}

custom_hardest_list_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="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/tv_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/tv_gender"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/tv_score"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

代码运行结果如下：

其实这个demo也可以用最简单的方式来实现，那就是重写Student类的toString()方法。

public String toString() {
    return "姓名:" + name + "\n性别:" + gender + "\n成绩:" + score;
}

ArrayAdapter的List操作

话不多说，直接上代码。

ListActionActivity.java:

public class ListActionActivity extends Activity implements View.OnClickListener {

    private Button mBtnAdd, mBtnAddAll;
    private Button mBtnInsert, mBtnClear;
    private Button mBtnRemove, mBtnSort;
    private Button mBtnSetNotifyOnChangeOpen, mBtnSetNotifyOnChangeClose;
    private ListView mLv;
    private ArrayAdapter<String> mAdapter;

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

        mBtnAdd = (Button) findViewById(R.id.btn_add);
        mBtnAddAll = (Button) findViewById(R.id.btn_addAll);
        mBtnInsert = (Button) findViewById(R.id.btn_insert);
        mBtnClear = (Button) findViewById(R.id.btn_clear);
        mBtnRemove = (Button) findViewById(R.id.btn_remove);
        mBtnSort = (Button) findViewById(R.id.btn_sort);
        mBtnSetNotifyOnChangeOpen = (Button) findViewById(R.id.btn_setNotifyOnChangeOpen);
        mBtnSetNotifyOnChangeClose = (Button) findViewById(R.id.btn_setNotifyOnChangeClose);

        mLv = (ListView) findViewById(R.id.lv);
        mAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, Util.generateString(10));
        mLv.setAdapter(mAdapter);

        mBtnAdd.setOnClickListener(this);
        mBtnAddAll.setOnClickListener(this);
        mBtnInsert.setOnClickListener(this);
        mBtnClear.setOnClickListener(this);
        mBtnRemove.setOnClickListener(this);
        mBtnSort.setOnClickListener(this);
        mBtnSetNotifyOnChangeOpen.setOnClickListener(this);
        mBtnSetNotifyOnChangeClose.setOnClickListener(this);
    }


    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn_add:
                add();
                break;
            case R.id.btn_addAll:
                addAll();
                break;
            case R.id.btn_insert:
                insert();
                break;
            case R.id.btn_clear:
                clear();
                break;
            case R.id.btn_remove:
                remove();
                break;
            case R.id.btn_sort:
                sort();
                break;
            case R.id.btn_setNotifyOnChangeOpen:
                setNotifyOnChangeOpen();
                break;
            case R.id.btn_setNotifyOnChangeClose:
                setNotifyOnCHangeClose();
                break;
        }
    }

    private void add() {
        String add = "我是通过add()添加进来的";
        mAdapter.add(add);
    }

    private void addAll() {
        List<String> addAll = new ArrayList<>();
        addAll.add("addAll-item1");
        addAll.add("addAll-item2");
        mAdapter.addAll(addAll);
    }

    private void insert() {
        String insert = "insert到第二个位置";
        mAdapter.insert(insert, 1);
    }

    private void clear() {
        mAdapter.clear();
    }

    private void remove() {
        mAdapter.remove("item 1");
    }

    private void sort() {
    }

    private void setNotifyOnChangeOpen() {
        mAdapter.setNotifyOnChange(true);
    }

    private void setNotifyOnCHangeClose() {
        mAdapter.setNotifyOnChange(false);
    }
}

activity_action_list.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"
    tools:context=".MiddleArrayAdapterActivity">

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

        <Button
            android:id="@+id/btn_add"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="add" />

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

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

        <Button
            android:id="@+id/btn_insert"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="insert" />

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

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

        <Button
            android:id="@+id/btn_remove"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="remove" />

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

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

        <Button
            android:id="@+id/btn_setNotifyOnChangeOpen"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="setNotifyOnChangeOpen" />

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

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

</LinearLayout>

好了，ArrayAdapter的用法应该都讲完了。找个时间把Demo的代码放到git上去~本系列文章会持续更新，欢迎关注~

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