SimpleAdapter和RecyclerView纪录

好长时间没有记录了，平时都记在Notion里面了。这个Adapter还是自己记下吧。

SimpleAdapter,MainActivity里面的代码，SimpleAdapter需要对应好参数。

其中第四个参数是对应Map里的String对象，然后第五个参数是对应的单个的布局文件的id。

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        ArrayList<Map<String,Object>> listItem = new ArrayList<>();
        for (int i = 0; i < name.length; i++) {
            HashMap<String, Object> objectObjectHashMap = new HashMap<>();

            objectObjectHashMap.put("person",name[i]);
            objectObjectHashMap.put("desc",descs[i]);
            listItem.add(objectObjectHashMap);
        }

        SimpleAdapter simpleAdapter = new SimpleAdapter(this,listItem, R.layout.simple_item, new String[]{"person", "desc"},new  int[]{R.id.name,R.id.desc}) ;
        ListView listView = findViewById(R.id.list);
        listView.setAdapter(simpleAdapter);
    }
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单个的组件应该怎么放的布局文件

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


    <ImageView
        android:id="@+id/header"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <TextView
            android:id="@+id/name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            />
        <TextView
            android:id="@+id/desc"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            />

    </LinearLayout>
</LinearLayout>
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主布局文件很简单只有一个ListView

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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=".MainActivity">

    <ListView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:divider="#f00"
        android:headerDividersEnabled="false"/>

</androidx.constraintlayout.widget.ConstraintLayout>
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---

RecyclerView

RecyclerView很容易出错，我一开始的时候显示不出来发现好多人都有这个问题。集中在3点。

1. layoutManger

 LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);
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2. oncreateViewholder

    public PersonHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                View inflate = LayoutInflater.from(MainActivity.this).inflate(R.layout.item, null);
                return new PersonHolder(inflate,this);
            }
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3. getItemCount（自己的错）

      @Override
            public int getItemCount() {
                return personList.size();
            }
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Adapter像是连接viewholder和recycler的桥梁。
需要构建的xml文件是在Adapter里的onCreat时加载的。然后返回自己创建的Viewholder

  RecyclerView.Adapter<PersonHolder> personHolderAdapter = new RecyclerView.Adapter<PersonHolder>() {
            @NonNull
            @Override
            public PersonHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                View inflate = LayoutInflater.from(MainActivity.this).inflate(R.layout.item, null);
                return new PersonHolder(inflate,this);
            }

            @Override
            public void onBindViewHolder(@NonNull PersonHolder holder, int position) {
                holder.nameTv.setText(personList.get(position).name);
                holder.descTv.setText(personList.get(position).desc);
                holder.headerIv.setImageResource(personList.get(position).header);
            }

            @Override
            public int getItemCount() {
                return personList.size();
            }
        };
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viewHolder集中在对应关系上

 class PersonHolder extends RecyclerView.ViewHolder{

        TextView nameTv;
        TextView descTv;
        ImageView headerIv;
        private RecyclerView.Adapter adapter;

        public PersonHolder(@NonNull View itemView,  RecyclerView.Adapter adapter) {
            super(itemView);
            this.headerIv = itemView.findViewById(R.id.header);
            this.nameTv = itemView.findViewById(R.id.name);
            this.descTv = itemView.findViewById(R.id.desc);
            this.adapter = adapter;
        }
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接下来就可以在MainActivity里构造了

      super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
         recyclerView = findViewById(R.id.recycler);
        recyclerView.setHasFixedSize(true);


        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);
//省略Adapter
        recyclerView.setAdapter(personHolderAdapter);

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