后台任务

Service

• 组件必须注册
• 服务并不是运行在一个独立的进程中，而是依赖于创建服务时所在的应用程序进程中。应用程序被杀死时，所有依赖它的服务都会停止
• 要在服务的内部创建子线程执行具体任务，否则默认运行在主线程，有可能出现主线程被阻塞的情况
• activity_my2.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="startService"
            android:onClick="startService"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="stopService"
            android:onClick="stopService"/>

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="bindService"
            android:onClick="bindService"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="unbindService"
            android:onClick="unbindService"/>

    </LinearLayout>

</LinearLayout>

• MyService.java

package com.example.myactivity1;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;

import androidx.annotation.Nullable;

public class MyService extends Service {

    private static final String TAG = "xxx";

    @Override
    public void onCreate() {
        super.onCreate();
        Log.d(TAG, "onCreate: ");
    }

    @Override
    public void onStart(Intent intent, int startId) {
        super.onStart(intent, startId);
        Log.d(TAG, "onStart: ");
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d(TAG, "onStartCommand: ");
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy: ");
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Log.d(TAG, "onBind: ");
        return null;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        Log.d(TAG, "onUnbind: ");
        return super.onUnbind(intent);
    }
}

• MyActivity2.java

package com.example.myactivity1;

import androidx.appcompat.app.AppCompatActivity;

import android.app.Service;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.view.View;

public class MyActivity2 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my2);
    }

    // 关闭activity后会在后台运行
    public void startService(View view) {
        /**
         * onCreate() -> onStartCommand() -> onStart()
         */
        startService(new Intent(this, MyService.class));
    }

    public void stopService(View view) {
        /**
         * onDestroy()
         */
        stopService(new Intent(this, MyService.class));
    }

    // 与activity共存亡
    public void bindService(View view) {
        /**
         *onCreate() -> onBind()
         */
        bindService(new Intent(this, MyService.class), connection, BIND_AUTO_CREATE);
    }

    public void unbindService(View view) {
        /**
         *onUnbind() -> onDestroy
         */
        unbindService(connection);
    }

    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {

        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {

        }
    };

    // 一般写法，当activity销毁时，自动解绑服务

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unbindService(connection);
    }
}

Handler

• MainActivity.java

package com.example.mythread;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    public static final int UPDATE_TEXT = 1;
    private TextView textView;
    private Button button;

    @SuppressLint("HandlerLeak")
    private Handler handler = new Handler(){
        public void handleMessage(Message msg){
            switch (msg.what){
                case UPDATE_TEXT:
                    Toast.makeText(MainActivity.this, "handleMessage", Toast.LENGTH_SHORT).show();
                    textView.setText("xixi");
                    break;
                default:
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = findViewById(R.id.tv);
        button = findViewById(R.id.btn);
        button.setOnClickListener(this);

    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btn:
                Toast.makeText(MainActivity.this, "onClick", Toast.LENGTH_SHORT).show();
                new Thread(()->{
                    Message message = new Message();
                    message.what = UPDATE_TEXT;
                    handler.sendMessage(message);
                }).start();
                break;
            default:
        }
    }
}

AsyncTask