尝试将数据加载到listview后Android应用程序崩溃

时间：2017-05-31 19:57:32

标签： java android

经过大量的尝试和一些关于android编程的知识我想从我的数据库中获取数据，但是我的应用程序崩溃了我称之为我的功能的所有内容＆＃34; populateDrinkerslijst＆＃34;

这是我的主要活动：

public class MainActivity extends AppCompatActivity {

private static final String TAG = "MainActivity";
private SectionsPageAdapter mSectionsPageAdapter;
private ViewPager mViewPager;
DatabaseHelper mDatabaseHelper;
private ListView mListView;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d(TAG, "onCreate: Starting.");
    mListView = (ListView) findViewById(R.id.drinkers_lijst);

    mSectionsPageAdapter = new SectionsPageAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.container);
    setupViewPager(mViewPager);

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(mViewPager);

    mDatabaseHelper = new DatabaseHelper(this);
    populateDrinkersLijst()


}

public void populateDrinkersLijst() {
    Cursor data = mDatabaseHelper.getDrinkers();

    ArrayList<String> listData = new ArrayList<>();
    listData.add("test");

    while (data.moveToNext()) {
        listData.add(data.getString(1));
    }

    ListAdapter adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, listData);
    mListView.setAdapter(adapter);


}

private void setupViewPager(ViewPager viewPager) {
    SectionsPageAdapter adapter = new SectionsPageAdapter(getSupportFragmentManager());
    adapter.addFragment(new home_fragment(), "Home");
    adapter.addFragment(new scan_pintje(), "scan pintje");
    adapter.addFragment(new controleer_pintje(), "controle pintje");
    adapter.addFragment(new beste_zuiper(), "beste drinkers");
    viewPager.setAdapter(adapter);
}
}

这是我的数据库类：

public class DatabaseHelper extends SQLiteOpenHelper {

private static final String TABLE_NAME = "pintjes_table";
private static final String COL1 = "ID";
private static final String COL2 = "name";
private static final String COL3 = "barcode";



public DatabaseHelper(Context context) {
    super(context, TABLE_NAME, null, 1);
}

@Override
public void onCreate(SQLiteDatabase db) {
    String createTable = "CREATE TABLE IF NOT EXIST " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT, " +
            COL2 + " TEXT, " + COL3 + " TEXT)";
    db.execSQL(createTable);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP IF TABLE EXISTS " + TABLE_NAME );
    onCreate(db);
}

public boolean addData(String naam,String barcode) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues contentValues = new ContentValues();
    contentValues.put(COL2,naam);
    contentValues.put(COL3,barcode);

    long result = db.insert(TABLE_NAME, null, contentValues);

    if(result == -1){
        return false;
    }else{
        return true;
    }
}

public Cursor getDrinkers(){
    SQLiteDatabase db = this.getWritableDatabase();
    String query = "SELECT * FROM " + TABLE_NAME;
    //String query = "SELECT " + COL2 + ",count(" + COL2 + ") AS aantal FROM " + TABLE_NAME + " GROUP BY " + COL2 + " ORDER BY aantal DESC";
    Cursor data = db.rawQuery(query, null);
    return data;

}

并且它一直在崩溃：

ArrayList<String> listData = new ArrayList<>();
    listData.add(1, "test");

    while (data.moveToNext()) {
        listData.add(data.getString(1));
    }

编辑：

调试后出现此错误：

  

java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.widget.ListView.setAdapter（android.widget.ListAdapter）＆＃39;在空对象引用上

3 个答案:

答案 0 :(得分：1)

你声明了listData by
ArrayList<String> listData = new ArrayList<>();

listData是一个arraylist而不是HashMap。  您无法将键值添加到ArrayList。

listData.add(1, "test");   //this is not correct

您只能添加字符串

listData.add("test");      //this is correct

答案 1 :(得分：0)

1。在从null获取data之前添加value检查。

2。使用listData.add("test")而不是listData.add(1, "test")将字符串添加到列表中。

3。确保您的layout包含ListView drinkers_lijst并使用ArrayAdapter<String>代替ListAdapter<String>。

更新方法populateDrinkersLijst()，如下所示： 

public void populateDrinkersLijst() {

    Cursor data = mDatabaseHelper.getDrinkers();

    ArrayList<String> listData = new ArrayList<>();
    listData.add("test");

    // Check weather cursor is empty
    if(data.moveToFirst())
    {
        do
        {
            listData.add(data.getString(1));

        }while(data.moveToNext());
    }

    // Close cursor  
    data.close();

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, listData);
    mListView.setAdapter(adapter);
}

<强>更新

当您使用ViewPager多个Fragments时。您应该为views类的片段初始化Fragment。

将ListView相关代码移至您的片段beste_zuiper。更新MainActivity和beste_zuiper课程如下：

<强> MainActivity.java： 

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    private SectionsPageAdapter mSectionsPageAdapter;
    private ViewPager mViewPager;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "onCreate: Starting.");

        mSectionsPageAdapter = new SectionsPageAdapter(getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.container);
        setupViewPager(mViewPager);

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(mViewPager);
    }

    private void setupViewPager(ViewPager viewPager) {

        mSectionsPageAdapter.addFragment(new home_fragment(), "Home");
        mSectionsPageAdapter.addFragment(new scan_pintje(), "scan pintje");
        mSectionsPageAdapter.addFragment(new controleer_pintje(), "controle pintje");
        mSectionsPageAdapter.addFragment(new beste_zuiper(), "beste drinkers");
        viewPager.setAdapter(mSectionsPageAdapter);
    }
}

<强> beste_zuiper.java： 

public class beste_zuiper extends android.support.v4.app.Fragment {
    private static final String TAG = "bestezuiperfragment";


    DatabaseHelper mDatabaseHelper;
    private ListView mListView;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.beste_zuiper_fragment, container, false);

        mListView = (ListView) view.findViewById(R.id.drinkers_lijst);

        mDatabaseHelper = new DatabaseHelper(getActivity());

        populateDrinkersLijst();

        return view;
    }

    public void populateDrinkersLijst() {

        Cursor data = mDatabaseHelper.getDrinkers();

        ArrayList<String> listData = new ArrayList<>();
        listData.add("test");

        // Check weather cursor is empty
        if(data.moveToFirst())
        {
            do
            {
                listData.add(data.getString(1));

            }while(data.moveToNext());
        }

        // Close cursor
        data.close();

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, listData);
        mListView.setAdapter(adapter);
    }
}

希望这会起作用〜

答案 2 :(得分：0)

问题是您使用过ArrayList.add(int index, E element)。当您尝试将位置IndexOutOfBoundsException的值插入空列表时，您的代码会抛出1异常。最简单的修复方法是从0开始。但通常你不关心元素位置，你只想将值附加到列表中。因此，只需使用ArrayList.add(E element)方法即可。

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