Listview 添加第二项后只显示一项

Question

为什么我的自定义列表视图只显示通过单击 window 中的 "add" 按钮在 EditText 中键入的最新数据（列表视图中只有一行），右边应该附加在列表视图项的下一行中，将数据保存并读取到 .dat 文件中。任何人都可以帮助我使用下面的代码吗？

这是我的 MainActivity 代码：

public class MainActivity extends AppCompatActivity implements 
View.OnClickListener {

private EditText edText;
private Button btnAdd;
private DatePickerDialog.OnDateSetListener dpdDateTimePicker;
private TextView tvDate;
private TextView tvListItem;
private TextView tvListDate;

private ArrayList<Items> arrItem;
private ItemListAdapter adapter;

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

    edText = findViewById(R.id.edText);
    btnAdd = findViewById(R.id.btnAdd);
    tvDate = findViewById(R.id.tvDate);

    tvListItem = findViewById(R.id.tvItem);
    tvListDate = findViewById(R.id.tvDate);

    ListView lvItemList = (ListView) findViewById(R.id.lvItem);

    //Date start
    tvDate.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Calendar cal = Calendar.getInstance();
            int year = cal.get(Calendar.YEAR);
            int month = cal.get(Calendar.MONTH);
            int day = cal.get(Calendar.DAY_OF_MONTH);

            DatePickerDialog dialog = new DatePickerDialog(MainActivity.this,
                    android.R.style.Theme_Holo_Dialog_MinWidth,
                    dpdDateTimePicker,
                    year, month,day);
            dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
            dialog.show();
        }
    });

    dpdDateTimePicker = new DatePickerDialog.OnDateSetListener() {
        @Override
        public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
            month = month + 1;
            String date = dayOfMonth + "/" + month + "/" + year;
            tvDate.setText(date);
        }
    };
    //Date end

    //Read Data
    arrItem = FileHelper.readData(this);

    adapter = new ItemListAdapter(this, R.layout.adapter_view_layout, arrItem);
    lvItemList.setAdapter(adapter);

    btnAdd.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    switch (v.getId()){
        case R.id.btnAdd:
            ListView lvItemList = (ListView) findViewById(R.id.lvItem);

            String itementered = edText.getText().toString();
            String dateentered = tvDate.getText().toString();

            Items item1 = new Items(itementered, dateentered);

            ArrayList<Items> ItemList = new ArrayList<>();
            ItemList.add(item1);

            FileHelper.writeData(ItemList, this);

            adapter = new ItemListAdapter(this, R.layout.adapter_view_layout, ItemList);
            lvItemList.setAdapter(adapter);

            //Clear TextView and EditText
            edText.setText("");
            tvDate.setText("");
            Toast.makeText(this,"Task Added", Toast.LENGTH_SHORT).show();
            break;

    }
}
}

FileHelper class 将 read/write 项目转化为 .dat

public class FileHelper {

public static final String FILENAME = "ItemList.dat";

public static void writeData(ArrayList<Items> item, Context context){
    try {
        FileOutputStream fos = context.openFileOutput(FILENAME, Context.MODE_PRIVATE);
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        oos.writeObject(item);
        oos.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public static ArrayList<Items> readData(Context context){
    ArrayList<Items> arItemList = null;

    try {
        FileInputStream fis = context.openFileInput(FILENAME);
        ObjectInputStream ois = new ObjectInputStream(fis);
        arItemList = (ArrayList<Items>) ois.readObject();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

    return arItemList;
}
}

我的自定义 ItemListAdapter

public class ItemListAdapter extends ArrayAdapter<Items> {

private Context mContext;
int mResource;

public ItemListAdapter(Context context, int resource, ArrayList<Items> objects) {
    super(context, resource, objects);
    this.mContext = context;
    this.mResource = resource;
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    //get the Item info
    String task = getItem(position).getTask();
    String date = getItem(position).getDate();

    //Create the task object with the information
    Items item = new Items(task, date);

    LayoutInflater inflater = LayoutInflater.from(mContext);
    convertView = inflater.inflate(mResource, parent, false);

    TextView tvDate = (TextView) convertView.findViewById(R.id.tvDate);
    TextView tvTask = (TextView) convertView.findViewById(R.id.tvItem);

    tvDate.setText(date);
    tvTask.setText(task);

    return convertView;

}
}

项目class

public class Items implements Serializable {
private String task;
private String date;

public Items(String task, String date) {
    this.task = task;
    this.date = date;
}

public String getTask() {
    return task;
}

public void setTask(String task) {
    this.task = task;
}

public String getDate() {
    return date;
}

public void setDate(String date) {
    this.date = date;
}
}

Answer 1

在你的 onClick 函数中，你总是创建一个新的 ArrayList<Items> ItemList 并向它添加一个 Items，然后你创建一个新的 ItemListAdapter，显示这个lvItemList.

中的新（单项）列表

代码应该更像下面。

@Override
public void onClick(View v) {
    switch (v.getId()){
        case R.id.btnAdd:
            ListView lvItemList = (ListView) findViewById(R.id.lvItem);

            String itementered = edText.getText().toString();
            String dateentered = tvDate.getText().toString();

            Items item1 = new Items(itementered, dateentered);

            //do not create a new ArrayList
                //ArrayList<Items> ItemList = new ArrayList<>();
                //ItemList.add(item1);
            //append item1 to the existing one instead
            arrItem.add(item1);

            //you might have to change this line to handle addition of single item
                //FileHelper.writeData(ItemList, this);
            //however after a quick look at FileHelper it seems that
            FileHelper.writeData(arrItem, this);    //might work

            //now you also don't need to/shouldn't create a new adapter
                //adapter = new ItemListAdapter(this, R.layout.adapter_view_layout, ItemList);
                //lvItemList.setAdapter(adapter);
            //just notify that arrItem has changed and the adapter will update the ListView
            adapter.notifyDataSetChanged();

            //Clear TextView and EditText
            edText.setText("");
            tvDate.setText("");
            Toast.makeText(this,"Task Added", Toast.LENGTH_SHORT).show();
            break;

    }
}

注意我还包括了 adapter.notifyDataSetChanged()，因为这确实是适配器方便的原因。您首先在 onCreate:

中将 adapter 设置为 lvItemList

adapter = new ItemListAdapter(this, R.layout.adapter_view_layout, arrItem);
lvItemList.setAdapter(adapter);

这会在 lvItemList 中显示 arrItem 的内容。如果您稍后希望添加项目，请将其添加到 arrItem 并调用 adapter.notifyDataSetChanged() 以显示更改。

关于 FileHelper 的注释。看起来 FileHelper.writeData() 重写了整个文件，因此写入 arrItem 应该会产生所需的结果，其中 lvItemList 中显示的所有项目也存储在文件中。

Listview 添加第二项后只显示一项

Listview only display one item after add the second item

android

listview

arraylist

custom-adapter