我要用 Realm 我创建了一个 provider class 保存值，但在主类中使用此类构造函数时( activity )显示此错误，请查看此图像中的错误：错误图像链接
任务提供程序类：

public class Task_Provider extends RealmObject {

    public Task_Provider() {
    }

    public String getAddTask() {
        return addTask;
    }

    public void setAddTask(String addTask) {
        this.addTask = addTask;
    }

    public long getAdded_date() {
        return added_date;
    }

    public void setAdded_date(long added_date) {
        this.added_date = added_date;
    }

    public long getWhen_date() {
        return when_date;
    }

    public void setWhen_date(long when_date) {
        this.when_date = when_date;
    }

    public boolean isComplete() {
        return complete;
    }

    public void setComplete(boolean complete) {
        this.complete = complete;
    }

    public Task_Provider(String addTask, long added_date, long when_date, boolean complete) {
        this.addTask = addTask;
        this.added_date = added_date;
        this.when_date = when_date;
        this.complete = complete;
    }

    private String addTask;
    @PrimaryKey
    private long added_date;
    private long when_date;
    private boolean complete;

}

主要活动（按钮setonclicklistener）：

String addTask = dialog_edit_task.getText().toString();
long now = System.currentTimeMillis();
RealmConfiguration realmConfiguration = new RealmConfiguration.Builder(getActivity()).build();
Realm.setDefaultConfiguration(realmConfiguration);
Realm realm = Realm.getDefaultInstance();
Task_Provider task_provider = new Task_Provider(addTask, now, 0, false);

realm.beginTransaction();
realm.copyToRealm(task_provider);
realm.commitTransaction();
realm.close();

我怎样才能解决这个问题？tnx全部<3