无法启动组件活动组件信息空指针异常

Question

我不确定如何在 Logcat 输出中找到行号。另外，使用这个最新的 Android Studio 版本，常规的 logcat 不起作用，所以我必须启动 Android 设备监视器来查看它。我只能抓到一个png，所以对此表示诚挚的歉意。

这是 MainActivity 类：

public class MainActivity extends Activity {

ListView listView;

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

    listView = (ListView) findViewById(R.id.listViewCategories);
    String[] categories = getResources().getStringArray(R.array.categories_array);

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

    listView.setAdapter(adapter);
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            // ListView Clicked item index
            int itemPosition = position;
            // ListView Clicked item value
            String itemValue = (String) listView.getItemAtPosition(position);
            // Show Alert
            /*Toast.makeText(getApplicationContext(),
                    "Position: " + itemPosition + "  List Item: " + itemValue,
                    Toast.LENGTH_LONG)
                    .show();*/
            Intent intent = new Intent(MainActivity.this, DisplayResult.class);
            intent.putExtra("ITEMVALUE", itemValue);
            startActivity(intent);
        }


    });
}

}

这是第二个活动，DisplayResult：

public class DisplayResult extends Activity {

String selectedCategory;

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

    Bundle b = getIntent().getExtras();
    String selectedCategory = b.getString("ITEMVALUE");

    //Toast.makeText(DisplayResult.this, "Category passed: " + selectedCategory,
    // Toast.LENGTH_LONG).show();

    final ListView lv = (ListView) findViewById(R.id.listViewItems);
    ArrayList<Promise> results = null;
    lv.setAdapter(new MyCustomArrayAdapter(this, results));
} // end onCreate

public ArrayList<Promise> GetPromises() {
    String table = "promises";
    ArrayList<Promise> promises = new ArrayList<Promise>();
    Promise prms = new Promise();
    SQLiteDatabase newDB;
    //SQLiteDatabase db = MyDBHandler.getReadableDatabase();

    //ArrayList<Promise> results = null;
    ArrayList<Promise> results = new ArrayList<Promise>();

    try {
        MyDBHandler dbHandler = new MyDBHandler(this.getApplicationContext());
        newDB = dbHandler.getReadableDatabase();
        Cursor c = newDB.rawQuery("SELECT * FROM " + MyDBHandler.TABLE_NAME +
                " WHERE KEY_CATEGORY = ?", new String[]{selectedCategory});

        if (c != null) {
            if (c.moveToFirst()) {
                do {
                    String category = c.getString(c.getColumnIndex("KEY_CATEGORY"));
                    String book = c.getString(c.getColumnIndex("KEY_BOOK"));
                    String chapter = c.getString(c.getColumnIndex("KEY_CHAPTER"));
                    String verse = c.getString(c.getColumnIndex("KEY_VERSE"));
                    String word = c.getString(c.getColumnIndex("KEY_WORD"));
                    Promise promise = new Promise();
                    /*promise.add(Strings)
                    results.add(promise)*/
                    results.add(new Promise(category, book, chapter, verse, word));
                } while (c.moveToNext());
            } // end inner if
        } // end outer if
    } catch (SQLiteException se) {
        Log.e(getClass().getSimpleName(), "Could not create or open the database");
    } finally {

    }
    return results;
}

}

这是 DBHandler 类：

public class MyDBHandler extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "promisesdatabase.sqlite";

public static final String TABLE_NAME = "promises";

public static final String KEY_ROWID = "id";
public static final String KEY_CATEGORY = "category";
public static final String KEY_BOOK = "book";
public static final String KEY_CHAPTER = "chapter";
public static final String KEY_VERSE = "verse";
public static final String KEY_WORD = "word";

public MyDBHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
     String DATABASE_CREATE =
            "CREATE TABLE if not exists " + TABLE_NAME + " (" +
                    KEY_ROWID + "integer PRIMARY KEY," +
                    KEY_CATEGORY + " TEXT," +
                    KEY_BOOK + " TEXT," +
                    KEY_CHAPTER + " TEXT," +
                    KEY_VERSE + " TEXT," +
                    KEY_WORD + " TEXT" + ")";

     db.execSQL(DATABASE_CREATE);
}

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

这是 CustomArrayAdapter 类：

public class MyCustomArrayAdapter extends ArrayAdapter {

private static ArrayList<Promise> promiseArrayList;

private LayoutInflater mInflater;

public MyCustomArrayAdapter(Context context, ArrayList<Promise> results) {
    super(context, 0, results);
    promiseArrayList = results;
    mInflater = LayoutInflater.from(context);
}
public int getCount() {
    return promiseArrayList.size();
}
public Object getItem(int position) {
    return promiseArrayList.get(position);
}
public long getItemId(int position) {
    return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // Get the data item for this position
    // Promise Promise = getItem(position); took out due to other blog geekswithblogs
    // Check if an existing view is being reused, otherwise inflate the view
    ViewHolder holder; // view lookup cache stored in tag
    if (convertView == null) {
        convertView = mInflater.inflate(R.layout.verses, null);
        holder = new ViewHolder();
        //LayoutInflater inflater = LayoutInflater.from(getContext());
        //convertView = inflater.inflate(R.layout.verses, parent, false);
        holder.txtcategory = (TextView) convertView.findViewById(R.id.txtViewCategory);
        holder.txtbook = (TextView) convertView.findViewById(R.id.txtViewBook);
        holder.txtchapter = (TextView) convertView.findViewById(R.id.txtViewChapter);
        holder.txtverse = (TextView) convertView.findViewById(R.id.txtViewVerse);
        holder.txtword = (TextView) convertView.findViewById(R.id.txtViewWord);
        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }
    // Populate the data into the template view using the data object
    holder.txtcategory.setText(promiseArrayList.get(position).getCategory());
    holder.txtbook.setText(promiseArrayList.get(position).getBook());
    holder.txtchapter.setText(promiseArrayList.get(position).getChapter());
    holder.txtverse.setText(promiseArrayList.get(position).getVerse());
    holder.txtword.setText(promiseArrayList.get(position).getWord());
    // Return the completed view to render on screen
    return convertView;
}
private static class ViewHolder {
    TextView id;
    TextView txtcategory;
    TextView txtbook;
    TextView txtchapter;
    TextView txtverse;
    TextView txtword;
}

还有一个 Promise 类（数据模型），但我认为没有必要发布。

这是 logcat png

Answer 1

我可能是错的，但应该行

ArrayList<Promise> results = null;

未读

ArrayList<Promise> results = GetPromises();

问题似乎是 DisplayResult 中的 ListView 正在尝试使用来自 MyCustomAdapter 的数据进行显示，该数据被赋予 null 而不是有效的 Promises ArrayList。