ListView和RecycleView使用

ListView

1. 定义list中基本项的布局方式

2. 定义list中基本项对应的类

   public class Fruit {
       private String name;
   
       public Fruit(String name) {
           this.name = name;
       }
   
       public String getName() {
           return name;
       }
   
       public void setName(String name) {
           this.name = name;
       }
   }
   

3. 在需要添加list的活动布局内添加ListView

4. 编写一个适配器类，该适配器类继承自ArrayAdapter类，适配器类内重写需要的构造方法，并且需要重写ArrayAdapter类的getView方法

   public class FruitAdapter extends ArrayAdapter {
       private int resourceId;
   
       public FruitAdapter(@NonNull Context context, int resource, @NonNull List objects) {
           super(context, resource, objects);
           resourceId = resource;
       }
       
        @Override
       public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        Fruit fruit = getItem(position);
           ViewHolder viewHolder;
           //减少实例化view次数
           if (convertView == null) { 
               view = LayoutInflater.from(getContext()).inflate(resourceId, null);
               //减少
               viewHolder = new ViewHolder();
               viewHolder.imageView = (ImageView) view.findViewById(R.id.fruit_item_iv_1);
               viewHolder.textView = (TextView) view.findViewById(R.id.fruit_item_tv_1);
               view.setTag(viewHolder)
           } else {
               view = convertView;
               viewHolder = (ViewHolder) view.getTag();
           }
           viewHolder.imageView.setImageResource(R.drawable.ic_launcher);
           viewHolder.textView.setText(fruit.getName());
           //TextView textView = (TextView) findViewById(R.id.fruit_item_tv_1);
           //textView.setText(fruit.getName());
           return view;
       }
       
       class ViewHolder {
           ImageView imageView;
           TextView textView;
       }
   }
   
   
   

   实例化该适配器类时需要传入需要传入基本项布局资源id，将该布局资源id保存起来；重写getVIew方法内，首先获取了传入的 objects对应 position位置的基本项类；判断基本布局项之前是否已经加载过，如果没有，通过LayoutInflater找到基本项布局并将其实例化，如果有的化，直接获取该基本布局项即可；通过基本项布局找到textview控件，将控件中的内容设置为拿到实体类内对应的内容;最后将实例化的布局返回；

5. 再活动内使用

   public class FruitActivity extends AppCompatActivity {
       private String[] data = {"Apple", "Banana", "Orange", "Pear", "Grape"};
       private List fruits = new ArrayList<>();
   
   
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_fruit);
           init();
           FruitAdapter fruitAdapter = new FruitAdapter(this, R.layout.fruit_item, fruits);
           ListView listView = (ListView) findViewById(R.id.activity_fruit_lv_1);
           listView.setAdapter(fruitAdapter);
           //添加监听事件
           listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
               @Override
               public void onItemClick(AdapterView parent, View view, int position, long id) {
                   Fruit fruit = fruits.get(position);
                   Toast.makeText(FruitActivity.this, "111111111111", Toast.LENGTH_SHORT).show();
               }
           });
       }
    
    //往fruits内填充数据
       public void init() {
           for (int i = 0; i< 4; i++) {
               for (int j=0; j< data.length; j++) {
                   fruits.add(new Fruit(data[j]));
               }
           }
       }
   }
   

RecycleView

1. 添加recycleView依赖

   `implementation 'androidx.recyclerview:recyclerview:1.1.0'

2. 定义list中基本项的布局方式，同上

3. 在需要添加list的活动布局中添加recycleView

4. 创建一个适配器类，该类继承自RecyclerView.Adapter，并重写其onCreateViewHolder， onBindViewHolder， getItemCount方法

   public class RvFruitAdapter extends RecyclerView.Adapter {
       private List mFruitList;
   
       static class ViewHolder extends RecyclerView.ViewHolder {
           ImageView imageView;
           TextView textView;
   
           public ViewHolder(@NonNull View itemView) {
               super(itemView);
               imageView = (ImageView) itemView.findViewById(R.id.fruit_item_iv_1);
               textView = (TextView) itemView.findViewById(R.id.fruit_item_tv_1);
           }
       }
   
       public RvFruitAdapter(List fruits) {
           mFruitList = fruits;
       }
   
    //若需要添加监听事件，在该函数内添加即可（通过view拿到组件添加监听事件)
       @NonNull
       @Override
       public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
           View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false);
           return new ViewHolder(view);
       }
   
       @Override
       public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
           Fruit fruit = mFruitList.get(position);
           holder.imageView.setImageResource(R.mipmap.ic_launcher);
           holder.textView.setText(fruit.getName());
       }
   
       @Override
       public int getItemCount() {
           return mFruitList.size();
       }
   
   
   }
   

   getItemCount方法需要返回列表长度，该方法将影响界面最终返回的基本项数量

5. 在活动内引用

   public class RecycleViewActivity extends AppCompatActivity {
       private String[] data = {"Apple", "Banana", "Orange", "Pear", "Grape"};
       private List fruits = new ArrayList<>();
   
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_recycle_view);
           init();
           RecyclerView recyclerView = (RecyclerView) findViewById(R.id.activity_recycle_view_rv_1);
           LinearLayoutManager layoutManager = new LinearLayoutManager(this);
           //网格布局
           //GridLayoutManager gridLayoutManager = new GridLayoutManager(this, 3);
           //瀑布布局
           //StaggeredGridLayoutManager staggeredGridLayoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL)
           recyclerView.setLayoutManager(layoutManager);
           recyclerView.setAdapter(new RvFruitAdapter(fruits));
       }
   
       public void init() {
           for (int i = 0; i< 4; i++) {
               for (int j=0; j< data.length; j++) {
                   fruits.add(new Fruit(data[j]));
               }
           }
       }
   }