Question

我想连接数据库中的数据并在列表视图中显示

但我在对象Realm中有错误并停止了我的应用程序

如何解决问题??

    protected void onResume() {
        super.onResume();
        Realm realm = Realm.getInstance(getApplicationContext());
        realm.beginTransaction();
        List<Car> cars = realm.allObjects(Car.class);
        String[] names = new String[cars.size()];
        for (int i = 0; i < names.length; i++) {
            names[i] = cars.get(i).getName();
        }


        ListView listView = (ListView) findViewById(R.id.listView);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1);

        listView.setAdapter(adapter);
    }

}

Answer 1

除了你没有指定logcat之外，Realm可能会告诉你，你已经打开了一个事务并且崩溃了。

您只需要将事务写入附加到领域的RealmObject。您还需要关闭打开的每个领域实例。您还必须注意，您无法从封闭的领域中读取。

例如，这有效：

Realm realm = null;
try {
    Cat cat = new Cat(); //public class Cat extends RealmObject {
    cat.setName("Meowmeow"); //cat is not yet attached to a realm, therefore you can modify it
    realm = Realm.getInstance(context); //open instance of default realm
    realm.beginTransaction();
    realm.copyToRealmOrUpdate(cat); //cat is now attached to the realm, 
                                    //and cannot be written outside the transaction.
    realm.commitTransaction();
} catch(Exception e) {
    if(realm != null) {
        try { //newer versions of Realm like 0.84.0+ have `realm.isInTransaction()`
            realm.cancelTransaction();
        } catch(IllegalStateException e) {
            //realm not in transaction
        }
    }
    throw e;
} finally {
    if(realm != null) {
        realm.close(); //every open realm must be closed
    }
}

如果您使用较新版本的Realm，也可以在后台线程上执行此操作，而无需手动打开和关闭所有内容。

realm.executeTransaction(new Realm.Transaction() {
    @Override
    public void execute(Realm realm) {
        // begin and end transaction calls are done for you
        Dog dog = realm.where(Dog.class).equals("age", 1).findFirst();
        d.setAge(3);
    }
}, new Realm.Transaction.Callback() {
    @Override
    public void onSuccess() {
        // Original RealmResults<T> objects and Realm objects 
        //     are automatically updated 
        // ON THREADS THAT HAVE A LOOPER ASSOCIATED WITH THEM (main thread)

        //the realm is written and data is updated, do whatever you want
    }
});

为了显示您的数据，这可行（0.83.0 +）：

public class HelloWorldActivity extends AppCompatActivity {
    protected Realm realm;

    ListView listView;

    @Override
    public void onCreate(Bundle bundle) {
        super.onCreate(bundle);
        realm = Realm.getInstance(this);
        setContentView(R.layout.activity_hello_world);
        this.listView = (ListView)findViewById(R.id.list_view);
        listView.setAdapter(new CarAdapter(this, realm.where(Car.class).findAll(), true);
    }

    @Override
    public void onDestroy() {
        realm.close();
    }
}

你需要一个适配器... listView ...

public class CarAdapter extends RealmBaseAdapter<Car> {
    public RealmModelAdapter(Context context, RealmResults<Car> realmResults, boolean automaticUpdate) {
        super(context, realmResults, automaticUpdate);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO 
        //implement viewholder pattern here: 
        //http://developer.android.com/training/improving-layouts/smooth-scrolling.html#ViewHolder
        //Listview is obsolete so I won't bother, 
        //use RecyclerView when you get the chance.
    }
}

android中Realm数据库出错

1 个答案: