Android Thread 介绍与实例
android中很重要的一个机制就是线程+消息，当然线程并不是android独有的，下面，简单的说说使用线程的时候应该注意的地方
我们采用最简单的方法来建立一个android的线程+消息的例子
1.thread + handler
[java]
package com.example.test_thread;
import android.app.activity;
import android.os.bundle;
import android.os.handler;
import android.os.message;
import android.widget.textview;
public class mainactivity extends activity {
textview mtextview = null;
// static textview mtextview = null;
@override
public void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
mtextview = (textview)findviewbyid(r.id.textview);
thread th = new thread(new runnable() {
@override
public void run() {
// todo auto-generated method stub
for(int i = 0;i<1000;i++)
{
try {
thread.sleep(500);
system.out.println("thread running :"+i+"!");
message msg = new message();
msg.what = i;
mhandler.sendmessage(msg);
} catch (interruptedexception e) {
// todo auto-generated catch block
e.printstacktrace();
}
}
}
});
th.start();
}
public handler mhandler = new handler(){
// public static handler mhandler = new handler(){
@override
public void handlemessage(message msg) {
// todo auto-generated method stub
super.handlemessage(msg);
mtextview.settext(string.valueof(msg.what));
}
};
}
package com.example.test_thread;
import android.app.activity;
import android.os.bundle;
import android.os.handler;
import android.os.message;
import android.widget.textview;
public class mainactivity extends activity {
textview mtextview = null;
// static textview mtextview = null;
@override
public void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
mtextview = (textview)findviewbyid(r.id.textview);
thread th = new thread(new runnable() {
@override
public void run() {
// todo auto-generated method stub
for(int i = 0;i<1000;i++)
{
try {
thread.sleep(500);
system.out.println("thread running :"+i+"!");
message msg = new message();
msg.what = i;
mhandler.sendmessage(msg);
} catch (interruptedexception e) {
// todo auto-generated catch block
e.printstacktrace();
}
}
}
});
th.start();
}
public handler mhandler = new handler(){
// public static handler mhandler = new handler(){
@override
public void handlemessage(message msg) {
// todo auto-generated method stub
super.handlemessage(msg);
mtextview.settext(string.valueof(msg.what));
}
};
}
当我们用以上方式建立线程时，进入应用之后，线程开始运行，handler接收消息改变ui中的textview，此时一切正常
当按下退出时，程序退出，但是程序进程还在stack中，因此主线程之子线程，也就是我们定义的th（th_1）不会退出，此时，在log信息中可以看到，system.out还在print数字
当再次进入程序的时候，可以看到，log中打印的信息double，但是ui会按照新线程（th_2）的次序改变
此时th_1仍在运行，th_1使用的 handler_1也在运行，只不过上一个activity的状态已经是finish，因此不会改变ui this ->mfinished= true
其实只要th_1中有关于上一个activity的引用，那么activity就不会销毁，java的机制就是这样，这是我们推荐的线程机制，下面着重说一下可能遇到的问题
2.同样是刚刚的例子，我们将handler定义成static
[java]
public static handler mhandler = new handler(){
public static handler mhandler = new handler(){此时，在退出应用再重新进入时，由于handler并不会有新的实例，因此，th_1与th_2同时发消息给一个static handler 或者说是指向了同一块内存区域，这时就会出现textview上的数字来回跳的现象
3.这样也可以
使用static定义handler也不是不可以，只要在activity的oncreate()中重新实例一个handler，这样，jvm分配另一块内存给新的handler，这样运行就正常了
[java]
package com.example.test_thread;
import android.app.activity;
import android.os.bundle;
import android.os.handler;
import android.os.message;
import android.widget.textview;
public class mainactivity extends activity {
public handler mhandler = null;
textview mtextview = null;
// static textview mtextview = null;
@override
public void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
mtextview = (textview)findviewbyid(r.id.textview);
mhandler = new testhandler();
thread th = new thread(new runnable() {
@override
public void run() {
// todo auto-generated method stub
for(int i = 0;i<1000;i++)
{
try {
thread.sleep(500);
system.out.println("thread running :"+i+"!");
message msg = new message();
msg.what = i;
mhandler.sendmessage(msg);
} catch (interruptedexception e) {
// todo auto-generated catch block
e.printstacktrace();
}
}
}
});
th.start();
}
class testhandler extends handler
{
@override
public void handlemessage(message msg) {
// todo auto-generated method stub
super.handlemessage(msg);
system.out.println("handler running :"+msg.what+"!");
mtextview.settext(string.valueof(msg.what));
}
}
}
package com.example.test_thread;
import android.app.activity;
import android.os.bundle;
import android.os.handler;
import android.os.message;
import android.widget.textview;
public class mainactivity extends activity {
public handler mhandler = null;
textview mtextview = null;
// static textview mtextview = null;
@override
public void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
mtextview = (textview)findviewbyid(r.id.textview);
mhandler = new testhandler();
thread th = new thread(new runnable() {
@override
public void run() {
// todo auto-generated method stub
for(int i = 0;i<1000;i++)
{
try {
thread.sleep(500);
system.out.println("thread running :"+i+"!");
message msg = new message();
msg.what = i;
mhandler.sendmessage(msg);
} catch (interruptedexception e) {
// todo auto-generated catch block
e.printstacktrace();
}
}
}
});
th.start();
}
class testhandler extends handler
{
@override
public void handlemessage(message msg) {
// todo auto-generated method stub
super.handlemessage(msg);
system.out.println("handler running :"+msg.what+"!");
mtextview.settext(string.valueof(msg.what));
}
}
}
当然，总的来说java还是不推荐使用static变量的，这本身也不符合面向对象的变成思想，所以，建议除了一些final值，尽量还是多使用消息机制来解决问题，维护也轻松些