adapter(适配器)

    关键字  ListView ArrayAdapter , SimpleAdapter,自定义适配器

    当我们做界面的时候，想要界面跑起来，同时但我们点击的时候，机器做出回应，这时候我们

    首先就要用到

    ListView 实现界面一条一条的排列，当界面满格时可以向下滑动，但是每条界面没有信息，当

    我们想要有信息时就要用到adapter(适配器)，他是数据源与ListView之间建立桥梁,是实现可编辑的信息自由显示，类似于View控件，

    但是可以对每一条编辑页面的快速生成，避免了每一条信息的都需要重复编辑

    首先是ArrayAdapter

    ArrayAdapter的实现需要1.上下文(context) 2.一条TextView.xml文档，里面不能放任何其他控件 3.一维数组

    public class List_Array_Activity extends AppCompatActivity {

    public ListView mListView;

    

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_list__array_layout);//本类的activity_list__array_layout.xml 里面需要定义一个ListView控件

        mListView= (ListView) findViewById(R.id.ListView_first_view);//定义id好找

        

        String[] array = new String[]{"java","j2se","android","ui","css","structs","javascript","html","xml"};//一维数组的每一个对象都是依次显示的对象

        ArrayAdapter arrayadapter = new ArrayAdapter(this,R.layout.activity_demo__text_view_layout,array);

        //this指代context上下文，activity_demo__text_view_layout是TextView.xml文档，array是数组

        mListView.setAdapter(arrayadapter);//注册启动

    }

}

  SimpleAdapter是实现可编辑页面的适配器

  关键字 1.context应用上下文 2.编辑页面的xml文档 3.HashMap的键值对的键 4.自定义的界面xml文档里相应的编码

  public class Simple_Adapter_Activity extends AppCompatActivity implements AdapterView.OnItemClickListener{//点击是实现事件回应

    public ListView mListView;

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_simple__adapter_layout);

        mListView= (ListView) findViewById(R.id.ListView_Simple);

       ArrayList arrayList =listData();

       String[] from = {"icon","title","content"};//HashMap的键值对的键，用来标记不同的事件

       

       int[] to  = {R.id.simple_demo_imageview,R.id.simple_demo_textviewtitle,R.id.simple_demo_textviewcontent};

       //to 里面的每一id值都是自定义的界面xml文档里相应的编码

       SimpleAdapter simpleAdapter = new SimpleAdapter(this,arrayList,R.layout.activity_demo__simple_layout,from,to);

        

       mListView.setAdapter(simpleAdapter);

      

        mListView.setOnItemClickListener(this);//注册注册注册

    }

    public ArrayList listData(){

        ArrayList arrayList = new ArrayList();

        HashMap<String,Object> item = new HashMap<>();

        item.put("icon",R.drawable.liying6);//"icon"HashMap的键值对的键 R.drawable.liying6是具体的值

        item.put("title","赵丽颖");

        item.put("content","资料");

        arrayList.add(item);

        item = new HashMap<>();

        item.put("icon",R.drawable.liying6);

        item.put("title","赵丽颖");

        item.put("content","资料");

        arrayList.add(item);

  return arrayList;

    }

    @Override

    public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {//接口 AdapterView.OnItemClickListener的方法

        switch(i){//HashMap的值从零开始

            case 0:

                Intent intent = new Intent(this, Android_log_Activity.class);

                startActivity(intent);

                break;

            case 1:

               intent = new Intent(this, Button_activity.class);

                startActivity(intent);

                break;

            case 2:

              intent = new Intent(this, Code_Activity.class);

                startActivity(intent);

                break;

            case 3:

                intent = new Intent(this, Linear_Activity.class);

                startActivity(intent);

                break;

        }

        MySimpleAdapter mySimpleAdapter = (MySimpleAdapter) adapterView.getAdapter();//得到mySimpleAdapter不能用new

        HashMap<String ,Object> item = (HashMap<String, Object>) mySimpleAdapter.getItem(i);//得到HashMap的具体对象

        String title = (String) item.get("title");

        String content = (String) item.get("content");

        

        Snackbar.make(view,title,Snackbar.LENGTH_SHORT).show();

    }

    自定义适配器

    客户的想法总是千奇百怪，为了满足需要，我们可以自己定义一个适配器

    public class MySimpleAdapter extends BaseAdapter {//自定义适配器必须继承BaseAdapter

    

    public List<HashMap<String,Object>> list = new ArrayList<>();//本适配器打算的用途

    public LayoutInflater layoutInflater;//解析器，布局文件的解析全靠它

    

    public MySimpleAdapter(Context context,List<HashMap<String,Object>> list){

        this.list=list;

        layoutInflater = LayoutInflater.from(context);

    }

    public int getCount() {

        return list.size();//List<HashMap<String,Object>>所装的对象多少

    }

    @Override

    public Object getItem(int i) {

        return list.get(i);//得到HashMap的具体对象

    }

    @Override

    public long getItemId(int i) {//得到HashMap的具体对象的id

        return i;

    }

    @Override

    public View getView(int i, View view, ViewGroup viewGroup) {

        View v = layoutInflater.inflate(R.layout.activity_demo__simple_layout,null);//这是我们想要界面的视图activity_demo__simple_layout是xml基本布局，v 的布局就是它

        ImageView iconimag = (ImageView) v.findViewById(R.id.simple_demo_imageview);//activity_demo__simple_layout布局里每个控件的id

        TextView titletxt = (TextView) v.findViewById(R.id.simple_demo_textviewtitle);

        TextView contenttxt = (TextView) v.findViewById(R.id.simple_demo_textviewcontent);

        HashMap<String,Object> item = (HashMap<String, Object>) getItem(i);//获取存放的每一条项

        int icon = (int) item.get("icon");//通过键获得值

        String title = (String) item.get("title");

        String content  = (String) item.get("content");

        iconimag.setImageResource(icon);//从新赋值

        titletxt.setText(title);

        contenttxt.setText(content);

        return v;

    }

}