Question

我在从Activity 1启动intent后尝试从Activity 2中的DB显示一些数据，如：

{       case R.id.buttonRead:

            intent = new Intent(this, ListDataActivity.class);

            startActivity(intent);

            break;
}

ListDataActivity具有以下编码：

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

        ListView lv = (ListView) findViewById(R.id.view_all_data);

        String[] from = new String[] { DBHelper.COLUMN_NAME,
                DBHelper.COLUMN_LAST_NAME };

        int[] to = new int[] { R.id.textView_name_reflect,
                R.id.textView_last_name_reflect };

        // create Adapter

        SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,
                R.layout.item, datasource.getAllEmployees(), from, to,
                FLAG_REGISTER_CONTENT_OBSERVER);

        // make adapter available for list

        lv.setAdapter(adapter);

}

Manifest中的ListDataActivity保持不使用Intent Filter。当我单击按钮并启动ListDataActivity应用程序时。崩溃与NullPointerException。最有趣的是，当我从onCreate ListDataActivity删除ListView时，以正常方式运行显示空白屏幕。你能告诉我有什么问题吗？ enter image description here

<?xml version="1.0" encoding="utf-8"?>
<ListView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/view_all_data"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

</ListView>

来自DataSource的

方法

public Cursor getAllEmployees（）{

Log.d(LOG_TAG, "--- Rows in mytable: ---");

// make query of all data from the table and receive instance of Cursor

Cursor c = db.query(DBHelper.TABLE_STAFF, null, null, null, null, null,
        null);

return c;

}

尝试了以下

case R.id.buttonRead:


    ArrayList<String> value = datasource.getAllEmployees();

    intent.putStringArrayListExtra("123", (ArrayList<String>)value);

    startActivity(intent);

    break;

}

改变

public ArrayList<String> getAllEmployees() {

ArrayList<String> empList = new ArrayList<String>();

    empList.add("Start");

    return empList;

}

以及ListDataActivity

Intent intent = getIntent();

ArrayList<String> value = intent.getStringArrayListExtra("123");




ListView lv = (ListView) findViewById(R.id.view_all_data);



// create Adapter

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_1, value);

// make adapter available for list

lv.setAdapter(adapter);

它工作正常

更改了我的getAllEmployees以查看是否所有内容都正确使用DB

public void getAllEmployees（）{

open();

Log.d(LOG_TAG, "--- Rows in mytable: ---");

// make query of all data from the table and receive instance of Cursor

Cursor c = db.query(DBHelper.TABLE_STAFF, null, null, null, null, null,
        null);

// put cursor into position of the first row of required data, if no
// rows false will return

if (c.moveToFirst()) {

    // get columns numbers

    int idColIndex = c.getColumnIndex(DBHelper.COLUMN_ID);
    int nameColIndex = c.getColumnIndex(DBHelper.COLUMN_NAME);
    int lastnameColIndex = c.getColumnIndex(DBHelper.COLUMN_LAST_NAME);
    int positionColIndex = c.getColumnIndex(DBHelper.COLUMN_POSITION);
    int departmentColIndex = c
            .getColumnIndex(DBHelper.COLUMN_DEPARTMENT);
    int inttelColIndex = c.getColumnIndex(DBHelper.COLUMN_INT_TEL);
    int mobileColIndex = c.getColumnIndex(DBHelper.COLUMN_MOB_TEL);
    int homeColIndex = c.getColumnIndex(DBHelper.COLUMN_HOME_TEL);
    int officemailColIndex = c
            .getColumnIndex(DBHelper.COLUMN_OFFICE_E_MAIL);
    int personalmailColIndex = c
            .getColumnIndex(DBHelper.COLUMN_PERSONAL_E_MAIL);

    do {

        // getting values by column numbers and put them into log

        Log.d(LOG_TAG,
                DBHelper.COLUMN_ID + c.getInt(idColIndex) + "\n"
                        + DBHelper.COLUMN_NAME
                        + c.getString(nameColIndex)
                        + DBHelper.COLUMN_LAST_NAME
                        + c.getString(lastnameColIndex)
                        + DBHelper.COLUMN_POSITION
                        + c.getString(positionColIndex)
                        + DBHelper.COLUMN_DEPARTMENT
                        + c.getString(departmentColIndex)
                        + DBHelper.COLUMN_INT_TEL
                        + c.getString(inttelColIndex)
                        + DBHelper.COLUMN_MOB_TEL
                        + c.getString(mobileColIndex)
                        + DBHelper.COLUMN_HOME_TEL
                        + c.getString(homeColIndex)
                        + DBHelper.COLUMN_OFFICE_E_MAIL
                        + c.getString(officemailColIndex)
                        + DBHelper.COLUMN_PERSONAL_E_MAIL
                        + c.getString(personalmailColIndex));

        // move to next row, if no next then end loop

    } while (c.moveToNext());

} else

    Log.d(LOG_TAG, "0 rows");

c.close();

}

当我调用datasource.getAllEmployees（）时，我的日志工作正常。来自MainActivity，但当我尝试从ListDataActivity应用程序崩溃时调用它。 有人可以解释一下发生了什么吗？ 检查过DB一切正常。将ListView放入MainActivity时，一切正常。 为何不与其他活动合作？

Answer 1

您忘记在Oncreate（）方法中使用datasource.open()或datasource = new YOURCLASS(this)

Answer 2

很抱歉对stackoverflow社区感到烦恼，但似乎练习Android的长时间延迟对我起了作用。简单地忘了声明DataSource类的变量。人们对你所做的事情，对自己和对周围的事情都有所了解！

无法在另一个活动中显示ListView列表

2 个答案: