java - 获取 JSON 并在 ListView 上显示，并使用数组适配器强制关闭

Question

java运行并能够获取JSON，但无法在布局上显示并强制关闭。我不知道出了什么问题。我猜这是布局上的问题，但我不确定......

我已经在java中添加了日志，它显示java运行到最后并在logcat上显示我需要的所有内容。但它只是没有显示在布局上，之后应用程序被迫关闭。

public class MainActivity extends AppCompatActivity {

private ListView bookList;
private LinearLayout linearLayout;
private String file = "books.json";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    bookList = findViewById(R.id.bookList);

    String jsonStr_books = readAssetsFile(file);
    ArrayList books = jsonToArrayList_books(jsonStr_books);
    Log.v("myLog", "arrayList: " + books);

    ArrayAdapter<Book> arrayAdapter = new ArrayAdapter<Book>(
            this, R.layout.content_main, books);

    bookList.setAdapter(arrayAdapter);
    displayBookList(books);
    Log.v("myLog", "done");

}

public class Book {
    public String title;
    public String author;

    public String toString(){
        return title + " by " + author;
    }
}

public String readAssetsFile(String file) {
    String json = null;
    try {
        InputStream is = getAssets().open(file);
        int size = is.available();
        byte[] buffer = new byte[size];
        is.read(buffer);
        is.close();
        json = new String(buffer, "UTF-8");
    } catch (IOException ex) {
        ex.printStackTrace();
        return null;
    }
    return json;
}

public ArrayList<Book> jsonToArrayList_books(String jsonStr){
    JSONObject jsonObjTable;

    ArrayList<Book> arrayList = new ArrayList<>();
    try{
        jsonObjTable = new JSONObject(jsonStr);
        JSONArray jsonArrayTable = jsonObjTable.getJSONArray("books");

        for (int i=0; i<jsonArrayTable.length();i++){
            JSONObject jsonObjRow = jsonArrayTable.getJSONObject(i);
            Book book = new Book();

            book.title = jsonObjRow.getString("title");
            book.author = jsonObjRow.getString("author");

            arrayList.add(book);

        }

    }catch(JSONException e){
        Log.v("myLog", e.toString());
    }
    return arrayList;
}

private void displayBookList(ArrayList<Book> arrayList){
    String bookRow;

    for (int i = 0; i<arrayList.size();i++){
        bookRow = arrayList.get(i).toString();
        TextView tv = new TextView(getApplicationContext());
        tv.setText(bookRow);
        linearLayout = findViewById(R.id.bookListLayout);
        linearLayout.addView(tv);
        Log.v("myLog", i + "> " + bookRow);
    }
}


}

这是布局:

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout 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"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        tools:context=".MainActivity"
        tools:showIn="@layout/activity_main"
        android:id="@+id/bookListLayout"
        android:orientation="vertical"
        >

        <ListView
            android:id="@+id/bookList"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </LinearLayout>

这是 JSON:

"books":[
        {
        "id": "1",
        "title": "test",
        "author": "123"
        },
        {
        "id": "2",
        "title": "A Tale of Two Cities",
        "author": "Charles Dickens"
        },
        {
        "id": "3",
        "title": "Alice in Wonderland",
        "author": "Lewis Carroll"
        }
    ]
}

它应该在 ListView 上显示标题 + "by "+ 作者。

Answer 1

从java代码中删除LinearLayout，并且您不需要displayBookList方法也删除它。您已经将适配器传递给 ListView 。