java如何将主线程与创建的工作线程连接？

Question

嘿，我在安卓 studio java上使用房间数据库时遇到了麻烦。 当我点击save按钮时，我正试图保存一个类的组件。 但问题是，在主线程上使用save或download调用是一件坏事，因此我正在创建自己的线程，但是在该线程之外如何使用数据呢？我正在做这个的班级看起来像这样

更新：那么这应该有效吗

package com.example.jenso.paperseller;

import 安卓.arch.persistence.room.Room;
import 安卓.content.Intent;
import 安卓.os.Bundle;
import 安卓.os.PersistableBundle;
import 安卓.support.annotation.Nullable;
import 安卓.support.v7.app.AppCompatActivity;
import 安卓.view.View;
import 安卓.widget.Button;
import 安卓.widget.EditText;

public class CreateCustomer extends AppCompatActivity {
    EditText name;
    EditText address;
    EditText phonenumber;
    EditText email;
    Button saveCustomer;
    PapperSellerDatabase pd;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.create_customer);
        name = findViewById(R.id.nameInput);
        address = findViewById(R.id.addressInput);
        phonenumber = findViewById(R.id.phonenumberInput);
        email = findViewById(R.id.emailInput);
        saveCustomer = findViewById(R.id.saveInput);
        setTheDataBase();


        saveCustomer.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(CreateCustomer.this, MainActivity.class));
                pd.customerDao().insertAll(new Customer(name.getText().toString(),address.getText().toString(),phonenumber.getText().toString(),email.getText().toString()));
            }
        });




    }
    public void setTheDataBase(){
        new Thread(new Runnable() {
            @Override
            public void run() {
                //here you obtain data from async source
                PapperSellerDatabase pd = Room.databaseBuilder(getApplicationContext(),PapperSellerDatabase.class,"production")
                        .fallbackToDestructiveMigration()
                        .build();


            }
        }).start();



    }
}

在负载方面，我是这样做的

package com.example.jenso.paperseller;

import 安卓.arch.persistence.room.Room;
import 安卓.content.Intent;
import 安卓.os.Bundle;
import 安卓.support.design.widget.FloatingActionButton;
import 安卓.support.design.widget.Snackbar;
import 安卓.support.v7.app.AppCompatActivity;
import 安卓.support.v7.widget.LinearLayoutManager;
import 安卓.support.v7.widget.RecyclerView;
import 安卓.support.v7.widget.ThemedSpinnerAdapter;
import 安卓.support.v7.widget.Toolbar;
import 安卓.util.Log;
import 安卓.view.View;
import 安卓.view.Menu;
import 安卓.view.MenuItem;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    RecyclerView recyclerView;
    RecyclerView.Adapter adapter;
    List<Customer> customers;
    PapperSellerDatabase database;


    FloatingActionButton fab;
    private static final  String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        recyclerView = findViewById(R.id.recycler);
        customers = new ArrayList<>();


        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        adapter = new PapperRecyclerAdapter(customers,this);
        recyclerView.setAdapter(adapter);

        downloadTheData();

        fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d(TAG, "onClick: Do this when you click");
                startActivity(new Intent(MainActivity.this, CreateCustomer.class));
            }

        });



    }
    private void downloadTheData(){
        new Thread(new Runnable() {
            @Override
            public void run() {
                //here you obtain data from async source
                PapperSellerDatabase pd = Room.databaseBuilder(getApplicationContext(),PapperSellerDatabase.class,"production")
                        .fallbackToDestructiveMigration()
                        .build();


                customers = pd.customerDao().getAllCustomers();

            }
        }).start();




    }




}

那么，如果我点击按钮，我想将数据保存到房间数据库，然后离开视图，我该怎么做呢

Answer 1

无论何时使用前提，例如在JavaScript中，您都不确定何时满足前提，或者换句话说，日期何时可用。所以通常要做的是在更高的范围内声明变量，这将使应该设置它的线程（worker）和应该使用它的线程（main）都可以使用它

更新

public class Example {
  //here you initialize your variable that will contain data
  List <RemoteData> remoteData = null;

  ....

  public void hereRemoteDataIsUsed(){
     if(remoteData != null){ 
        //use remoteData here
        ...
     }
  }

  ....
  public void hereRemoteDataIsSet(){
      new Thread(new Runnable() {
          @Override
          public void run() {
            //here you obtain data from async source     
            remoteData = getDataFromSomeAsyncSource();
          }
    }).start();
  }
}

您可以注意到，在获取数据的方法中，没有返回任何内容。因为它是一个异步操作，所以您不知道何时会完成。你只知道，终究会的。所以您只需等待它可用（remoteData != null）