Android Adapter:ArrayAdapter篇
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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textViewResourceIdif (mFieldId == 0) {// If no custom field is assigned, assume the whole resource is a TextViewtext = (TextView) view;} else {// Otherwise, find the TextView field within the layouttext = (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;@Overrideprotected 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"><ListViewandroid: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"><ImageViewandroid:layout_width="30dp"android:layout_height="30dp"android:src="@mipmap/ic_launcher" /><TextViewandroid: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;@Overrideprotected 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;}@Overridepublic 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;}@Overridepublic 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"><TextViewandroid:id="@+id/tv_name"android:layout_width="match_parent"android:layout_height="wrap_content" /><TextViewandroid:id="@+id/tv_gender"android:layout_width="match_parent"android:layout_height="wrap_content" /><TextViewandroid: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;@Overrideprotected 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);}@Overridepublic 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"><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="horizontal"><Buttonandroid:id="@+id/btn_add"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:text="add" /><Buttonandroid:id="@+id/btn_addAll"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:text="addAll" /></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="horizontal"><Buttonandroid:id="@+id/btn_insert"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:text="insert" /><Buttonandroid:id="@+id/btn_clear"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:text="clear" /></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="horizontal"><Buttonandroid:id="@+id/btn_remove"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:text="remove" /><Buttonandroid:id="@+id/btn_sort"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:text="sort" /></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="horizontal"><Buttonandroid:id="@+id/btn_setNotifyOnChangeOpen"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:text="setNotifyOnChangeOpen" /><Buttonandroid:id="@+id/btn_setNotifyOnChangeClose"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:text="setNotifyOnChangeClose" /></LinearLayout><ListViewandroid: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~
觉得文章不错的话,就赏我一罐可乐吧~