Question

我正在创建一个Android应用程序，它从用户获取任务详细信息并将其插入数据库。当用户想要查看当天的任务列表时（某些任务将显示不是所有任务），他将转到＆＃34; viewTasks.java＆＃34;扩展listActivity并使用服装适配器显示任务列表的活动。

列表视图从数据库中返回List<TodaysTask>的函数中获取其项。现在这个活动什么都没有！虽然我确信有任务插入数据库！定制列表不会出现在我身上！这有什么不对？

如果从数据库返回的列表不为空并且出现此消息，我还会添加Toast消息！你能帮我解决这个问题吗？ TodaysTask类具有字符串名称，类别和int time_H，time_M。

这里将向用户显示days任务的ViewTasks.java

public class ViewTask extends Activity implements 
    OnItemClickListener, DialogInterface.OnClickListener {

private ListView todays_task_list;
private List<TodayTasks> todaysTaskArrayList;
private CustomAdapter customAdapter;
private int clickedPosition;
SchedulerHelper schedulerHelper;

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

    schedulerHelper = new SchedulerHelper(this);
    schedulerHelper.open();

    todaysTaskArrayList = new ArrayList<TodayTasks>();
    todaysTaskArrayList = schedulerHelper.getTodayTasks();

    if (!todaysTaskArrayList.isEmpty())//has elements 
        Toast.makeText(getApplicationContext(), "not empty", Toast.LENGTH_SHORT)
        .show();

    todays_task_list = (ListView) findViewById(R.id.tasksList);
    customAdapter = new CustomAdapter(this, R.layout.list_row,
            todaysTaskArrayList);
    todays_task_list.setAdapter(customAdapter);
    todays_task_list.setOnItemClickListener(this);}

@Override
protected void onResume() {
    super.onResume();
    todaysTaskArrayList = new ArrayList<TodayTasks>();
    todaysTaskArrayList = schedulerHelper.getTodayTasks();
    customAdapter = new CustomAdapter(this, R.layout.list_row,
            todaysTaskArrayList);
    todays_task_list.setAdapter(customAdapter);
    todays_task_list.setOnItemClickListener(this); }

@Override
protected void onStart() {
    super.onStart();
    todaysTaskArrayList = new ArrayList<TodayTasks>();
    todaysTaskArrayList = schedulerHelper.getTodayTasks();
    customAdapter = new CustomAdapter(this, R.layout.list_row,
            todaysTaskArrayList);
    todays_task_list.setAdapter(customAdapter);
    todays_task_list.setOnItemClickListener(this);}

@Override
public void onItemClick(AdapterView<?> adapterView, View view,
        int position, long id) {//do somethings
}}

task_view.xml

<ListView
    android:id="@+id/tasksList"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_marginBottom="60dp"
    android:layout_marginTop="10dp"/>

这是定制的适配器代码段

public class CustomAdapter extends ArrayAdapter<TodayTasks> {
private Context context;

public CustomAdapter(Context context, int resource, List<TodayTasks> objects) {
    super(context, resource, objects);
    this.context = context;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View view = convertView;
    final int pos = position;
    if (convertView == null)
        view = LayoutInflater.from(getContext()).inflate(R.layout.list_row,
                null);

    // task name
    TextView name = (TextView) convertView.findViewById(R.id.task_name);

    // category name
    TextView category = (TextView) convertView
            .findViewById(R.id.task_category);

    // proposed_time
    TextView time = (TextView) convertView.findViewById(R.id.proposed_time);

    TodayTasks todaysTask = getItem(position);
    name.setText(todaysTask.name);
    category.setText(todaysTask.category);
    time.setText(String.format("%02d : %02d", todaysTask.time_H,
            todaysTask.time_M));

    view.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View view) {
            ((ViewTask) context).startOnClick(pos);
        }
    });
    return view;
}}

List_row.xml

 <TextView
    android:id="@+id/task_name"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/assignment"/>


<TextView
    android:id="@+id/task_category"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_below="@id/task_name"
    android:text="@string/university" />

<TextView
    android:id="@+id/proposed_time"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentRight="true"
    android:layout_alignTop="@id/title"
    android:gravity="right"
    android:layout_marginTop="10dp"
    android:text="@string/_16_30"/>

以及返回List片段的databaseHelper中的函数

public List<TodayTasks> getTodayTasks() {
    Cursor cursor = sqliteDatabase.query(TODAYTASKS_TABLE, null, null,
            null, null, null, null);
    ArrayList<TodayTasks> tasksInfo = new ArrayList<TodayTasks>();
    if (cursor != null && cursor.moveToFirst()) {
        do {
            tasksInfo
                    .add(new TodayTasks(
                            cursor.getString(cursor
                                    .getColumnIndex(COLUMN_NAME_TODAYTASKS_NAME)),
                            cursor.getString(cursor
                                    .getColumnIndex(COLUMN_NAME_TODAYTASKS_CATEGORY)),
                            cursor.getInt(cursor
                                    .getColumnIndex(COLUMN_NAME_TODAYTASKS_TIME_HOUR)),
                            cursor.getInt(cursor
                                    .getColumnIndex(COLUMN_NAME_TODAYTASKS_TIME_MINUTE))));

        } while (cursor.moveToNext());
    }
    if (!tasksInfo.isEmpty()) {
        cursor.close();
        return tasksInfo;
    } else {
        cursor.close();
        return null;
    }
}

Answer 1

如果您的活动扩展了列表活动，那么它应该有一个列表视图，其ID为android.R.id.list

<ListView android:id="@id/android:list"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/>

你可以用

查找

ListView lv = (ListView) findViewById(android.R.id.list);

Answer 2

使用此oncreate您的代码应该工作。如果没有发生其他错误，那么我们将看到。

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    //remove setcontentview()
        schedulerHelper = new SchedulerHelper(this);
        schedulerHelper.open();

        todaysTaskArrayList = new ArrayList<TodayTasks>();
        todaysTaskArrayList = schedulerHelper.getTodayTasks();

        if (!todaysTaskArrayList.isEmpty())//has elements 
            Toast.makeText(getApplicationContext(), "not empty", Toast.LENGTH_SHORT)
            .show();

        todays_task_list = getListView();//write this.
        customAdapter = new CustomAdapter(this, R.layout.list_row,
                todaysTaskArrayList);
        todays_task_list.setAdapter(customAdapter);
        todays_task_list.setOnItemClickListener(this);}




 @Override
    protected void onResume() {
        super.onResume();
        todaysTaskArrayList = new ArrayList<TodayTasks>();
        todaysTaskArrayList = schedulerHelper.getTodayTasks(); //this should be here
        customAdapter = new CustomAdapter(this, R.layout.list_row,
                todaysTaskArrayList);
        todays_task_list.setAdapter(customAdapter);
        todays_task_list.setOnItemClickListener(this);
       //instead of here.
       }

现在你的代码应该可以运行。

Answer 3

错误可能在这里

if (convertView == null)
    view = LayoutInflater.from(getContext()).inflate(R.layout.list_row,
            null);

更改为

if (convertView == null)
    view = LayoutInflater.from(getContext()).inflate(R.layout.list_row,
            parent);

也可以在onCreate Method

中使用

setListAdapter(customAdapter);

使用getView回调：

if(view == null){
  //inflate
}

而不是if（convertView == null）也低于使用视图而不是convertView并返回视图

自定义listView不起作用

3 个答案: