最近看了一下Android，只看书不总结一下，总感觉东西并没有放在脑子里，人过留名，雁过留声，遂写下这篇总结。
书本看的是《Android编程兵书》，但这篇总结的大纲是按照《第一行代码》的章节目录撰写的。两本书的内容结构大致相同，Android入门的话只看其中一本就够了。
Service：适合执行那些不需要和用户交互而且还要求长期运行的任务，不依赖于任何界面，依赖于创建服务所在的应用程序。
java创建线程的两种方法
// 方法一
class MyThread extends Thread{
public void run(){
}
}
new MyThread().start();
//方法二
class Mythread implements Runnable{
public void run(){
}
}
MyThread myThread = new MyThrea();
new Thread(myThread).start(); // Thread构造函数接收一个Runnable参数
//方法三 匿名类
new Thread(new Runnable(){
public void run(){
}
}).start();
Android 不允许在子线程中操作UI
解决方法：
Android异步处理机制示例代码
public class MainActivity extends Activity implements OnClickListener{
public static final int UPDATE_TEXT = 1;
private TextView text;
private Button changeText;
private Handler handler = new Handler(){
public void handleMessage(Message msg){
switch(msg.what){
case UPDATE_ETXT:
text.setText("Nice to meet you");
break;
default:
break;
}
}
}
public void onClick(View v){
switch(v.getId()){
case R.id.change_text:
new Thread(new Runnable(){
public void run(){
Message message = new Message();
message.what = UPDATE_ETXT;
handler.sendMessage(message);
}
}).start();
break;
default:
break;
}
}
}
使用AsyncTask 示例代码
class DownloadTask extends AsyncTask<Void, Integer, Boolean>{
protected void onPreExecute(){
progressDialog.show();
}
protected Boolean doInBackground(Void... params){
try{
while(true){
int downloadPercent = doDownload();
publishProgress(downloadPercent);
if(downloadPercent >= 100){
break;
}
}
}catch(Exception e){
e.printStackTrace();
}
return true;
}
protected void onProgressUpdate(Integer... values){
progressDialog.setMessage("Downloaded " + values[0] + "%");
}
protected void onPostExecute(Boolean result){
progressDialog.dismiss(); // 关闭进度对话框
if(result){
Toast.makeText(context, "Download successed ", Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(context, "Download failed", Toast.LENGTH_SHORT).show();
}
}
}
使用服务
onCreate()方法在服务第一次创建的时候调用，onStartCommand()方法则在每次启动服务的时候都会调用，只要在Service中的任何一个地方调用stopSelf()方法就能停止服务。还可用stopService()停止服务
activity绑定服务
public class MyService extends Service{
private DownloadBinder mBinder = new DownloadBinder();
class DownloadBinder extends Binder{
public void startDownload(){
Log.d("MyService", "startDownload executed");
}
public int getProgress(){
Log.d("MyService", "getProgress executed");
return 0;
}
}
public Ibinder onBind(Intent intent){
return mBinder;
}
public void onCreate(){
super.onCreate();
}
public onStartCommand(Intent intent, int flags, int startId){
return super.onStartCommand(intent, flags, startId);
}
public void onDestroy(){
super.onDestroy();
}
}
Myservice.DownloadBinder downloadBinder;
ServiceConnection connection - new ServiceConnection(){
public void onServiceDisconnected(ComponentName name){}
public void onServiceConnected(ComponentName name, Ibinder service){
downloadBinder = (Myservice.DownloadBinder) service;
downloadBinder.startDownload();
downloadBinder.getProgress();
}
}
Intent bindIntent = new Intent(this, MyService.class);
bindService(bindIntent, connection, BIND_AUTO_CREATE);// BIND_AUTO_CREATE参数表示绑定后自动创建服务，onCreate执行，onStartCommand不执行
//启动服务
Intent startIntent = new Intent(this, Myservice.class);
startService(startIntent);
//停止服务
Intent stopIntent = new Intent(this, MyService.class);
stopService(stopIntent);
前台服务：防止内存不足是系统收回后台服务。前台服务在状态栏有显示。
示例代码
// MyService 中
Notification notification = new Notification(R.drawable.ic_launcher, "Notification comes", System.currentTimeMillis());
Intent notificationIntent = new Intent(this, MainActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
notification.setLatestEventInfo(this, "this is title", "this is content", pendingIntent);
startForeground(1, notification);
使用IntentService:服务运行在子线程中且运行结束后自动停止，其余和普通Service相似
Android后台执行定时任务：方法有两种Java API的Timer类和Android的Alarm机制。Timer不适用于需要长期在后台执行的任务。Android会在长时间无操作的情况下让CPU进入睡眠状态，这可能导致Timer中的定时任务无法正常执行。Alarm机制则不存在此问题，因为Alarm具有唤醒CPU的功能
Android Alarm 示例代码
public void LongRunningService extends Service{
pubic Ibinder onBind(Intent intent){
return null;
}
public int onStartCommand(Intent intent, int flags, int startId){
new Thread(new Runnable(){
public void run(){
Log.d("LongRunningService", "executed at " + new Date().toString());
}
}).start();
AlarmManager manager = getSystemService(ALARM_SERVICE);
int anHour = 60 * 60 * 1000; // 一个小时的毫秒数
long triggerAtTime = SystemClock.elapsedRealtime() + anHour;
Intent i = new Intent(this, AlarmReceiver.class);
PendingIntent pi = PendingIntent.getBroadcast(this, 0, i, 0);
manager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, triggerAtTime, pi);
return super.onStartCommand(intent, flags, startId);
}
}
//在onReceive方法中再次启动LongRunningService，形成一个永久的循环
public class AlarmReceiver extends BroadcastReceiver{
pubic void onReceive(Context context, Intent intent){
Intent i = new Intent(context, LongRunningService.class);
context.startService(i);
}
}
Tips
1、iOS不支持后台，当应用程序不在前台运行时就会进入到挂起状态。
而Android沿用了Symbian的习惯加入了后台功能，使得应用程序即使在关闭的情况下仍然可以在后台继续运行。
2、若既调用了startService又调用了BindService，需要同时调用stopService和unbindService方法，onDestroy方法才会执行
3、什么是ANR？
Application Not Responding
网友评论