进程与线程的区别?
在Android中,线程是跑在进程之中的,当手机打开一个APP就相当于打开了一个进程,比如:UI界面的更新,就是在主线程中完成的,我也可以自定义一些子线程来完成所需要的任务.
如何创建线程?创建线程的几种方式?
1.创建一个类继承Thread类
2.创建一个类实现Runnable接口
什么是多线程?
线程是程序中一个单一的顺序控制流程,在程序中同是运行多个线程完成不同的工作,称为多线程
ANR的基础知识及产生?
ANR:application not responding :应用程序无响应
产生的情况:1.主要类型按键或触摸事件在特定的时间(5秒)内无响应
2.BroadcastReceiver在特定事件(10秒)内无法处理完成
3.小概率类型Service在特定事件内无法完成
线程的状态:
创建(new) ---->就绪(runnable)---->运行(running)---->阻塞(bloocked)----->消亡(dead)
当线程满足所需要运行的条件时,才能进入就绪状态
当线程就如就绪状态后,不能马上获得cpu的执行时间,需要CPU进行资源分配
当线程被中断后执行完毕才会被消亡
线程的生命周期
注意:多线程会导致CPU资源分配的增加导致系统繁忙
多线程示例:售票
package com.hejun.ticket;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
final static String TAG = "MainActivity";
private Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = findViewById(R.id.strat_sale);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
SaleTickets saleTickets1 = new SaleTickets(4);
SaleTickets saleTickets2 = new SaleTickets(3);
SaleTickets saleTickets3 = new SaleTickets(2);
SaleTickets saleTickets4 = new SaleTickets(2);
saleTickets1.setName("售票窗口1");
saleTickets2.setName("售票窗口2");
saleTickets3.setName("售票窗口3");
saleTickets4.setName("售票窗口4");
saleTickets1.start();
saleTickets2.start();
saleTickets3.start();
saleTickets4.start();
}
});
}
private class SaleTickets extends Thread{
private int tickets;
private SaleTickets(int tickets){
this.tickets = tickets;
}
@Override
public void run() {
super.run();
while(tickets>0){
Sale();
}
Log.d(TAG, Thread.currentThread().getName()+ "的票售卖完了");
}
private void Sale(){
tickets--;
Log.d(TAG, Thread.currentThread().getName()+ "正在卖票,还剩下"+ tickets +"张票");
}
}
}
演示结果
线程间通信的相关组件
1.Message :消息.其中包含了消息ID,消息处理对象以及处理数据,Message有MessagesQueue统一列队,最终有Handle处理
2.Handle:处理者,负责Message的发送及处理,实现handleMessage(Message msg)方法,对特定的MEssage进行处理
3.MessagesQueue:消息队列,用来存放Handle发送过来的消息,并按照先进先出规则执行
4.Looper:消息泵,不断的从MessagesQueue中抽取Message执行,一个MessagesQueue需要一个Looper
5.Thread:线程,辅助调度整个消息循环,即消息循环执行的场所
关系:Handle looper MessagesQueue是简单的三角关系Looper和MessagesQueue是一一对应的
消息循环
一个Message经由Handle发送到MessagesQueue队列中,再由Looper不断的从MessagesQueue抽取,又再一次回到Handle的环抱,实现线程间的通信
线程与更新
在ui线程中,如果创建Handle是不传入Looper对象,那么将直接使用UI\线程的Looer对象(系统已经帮我们自动创建了),在其他线程创建Handle如果不传入Looper对象,那么Handle将不能接收处理消息,在这种情况下,通常的做法是:
在创建Handle之前,为该线程准备好一个Looper(Looper.prepare),然后让这个Looper跑起来(Looper.loop),这样Handle 才能正常工作;.
注意:Handle处理消息总是在创建Handler的线程中执行,而我们的消息处理,不乏UI的更新操作,不正确的线程直接更新UI将引发异常,因此,我们需要时刻关心Handler是在哪个线程中创建的.
SDk提供四中方式可以从其他线程中访问UI线程
1.Activity.runOnUiThread(Runnable)
2.View.post(Runnable)
3.View.postDelayed(Runnable,long)
4.Handler
案例,从网上下载图片并更新进度
package com.hejun.ticket;
import android.annotation.SuppressLint;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;
import android.os.Trace;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class DownPicture extends AppCompatActivity {
final static String address = "http://img4.imgtn.bdimg.com/it/u=1952016862,1880307894&fm=26&gp=0.jpg";
private static final String TAG = "DownPicture";
private Handler mMainHandler = null;
private int progress;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_down_picture);
Button button = findViewById(R.id.button);
final ImageView imageView = findViewById(R.id.img);
button.setOnClickListener(new View.OnClickListener() {
@SuppressLint("HandlerLeak")
@Override
public void onClick(View view) {
final ProgressDialog progressDialog = new ProgressDialog(DownPicture.this);
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.setMessage("下载中");
progressDialog.setMax(100);
progressDialog.show();
new Thread(new Down(),"下载图片").start();
mMainHandler = new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch (msg.what){
case 10010:
progressDialog.setProgress(msg.arg1);
break;
case 10011:
progressDialog.dismiss();
Bitmap bitmap = (Bitmap) msg.obj;
imageView.setImageBitmap(bitmap);
break;
}
}
};
}
});
}
class Down implements Runnable {
String fileName = "dowmPicture";
@Override
public void run() {
try {
URL url = new URL(address);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setConnectTimeout(5000);
httpURLConnection.setRequestMethod("GET");
if (httpURLConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
InputStream inputStream = httpURLConnection.getInputStream();
OutputStream outputStream = openFileOutput(fileName, MODE_PRIVATE);
byte[] bytes = new byte[1024*1024];
int s = httpURLConnection.getContentLength();
int d = 0;
int curent = 0;
while ((d = inputStream.read(bytes)) != -1){
outputStream.write(bytes,0,s);
curent += d;
progress = (int) ((float)curent/s*100);
Log.d(TAG, "当前现在进度为" + progress);
SystemClock.sleep(40);
Message message = new Message();
message.arg1 = progress;
message.what = 10010;
mMainHandler.sendMessage(message);
}
if (progress == 100){
Bitmap bitmap = BitmapFactory.decodeFile(getFileStreamPath(fileName).getAbsolutePath());
Message message = new Message();
message.obj = bitmap;
message.what = 10011;
mMainHandler.sendMessage(message);
}
inputStream.close();
outputStream.close();
httpURLConnection.disconnect();
}
}
catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}