Android(安卓)Service 之四 问题总结
16lz
2021-01-25
http://rainbow702.iteye.com/blog/1142600
我写了一个 Service 的Demo,但是将启动Service的Intent声明为主Activity的成员变量时,
- publicclassMyServiceActivityextendsActivity{
- privateButtonstartSer1;
- privateButtonstopSer1;
- privateButtonstartSer2;
- privateButtonstopSer2;
- publicstaticTextViewlog;
- privateIntentintent=newIntent(MyServiceActivity.this,MyService.class);
- @Override
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- startSer1=(Button)findViewById(R.id.startSer1);
- stopSer1=(Button)findViewById(R.id.stopSer1);
- startSer2=(Button)findViewById(R.id.startSer2);
- stopSer2=(Button)findViewById(R.id.stopSer2);
- log=(TextView)findViewById(R.id.log);
- startSer1.setOnClickListener(btnListener);
- stopSer1.setOnClickListener(btnListener);
- startSer2.setOnClickListener(btnListener);
- stopSer2.setOnClickListener(btnListener);
- }
- privateOnClickListenerbtnListener=newOnClickListener(){
- @Override
- publicvoidonClick(Viewv){
- switch(v.getId()){
- caseR.id.startSer1:
- updateLog("StartService1pressed");
- startService(intent);
- break;
- caseR.id.startSer2:
- updateLog("StartService2pressed");
- startService(intent);
- break;
- caseR.id.stopSer1:
- updateLog("StopService1pressed");
- stopService(intent);
- break;
- caseR.id.stopSer2:
- updateLog("StopService2pressed");
- stopService(intent);
- break;
- default:
- break;
- }
- }
- };
- publicstaticvoidupdateLog(Stringtext){
- CharSequencech=log.getText();
- log.setText(((ch==null||ch.length()==0)?text:ch.toString()
- +"\r\n"+text));
- }
- }
系统总是在启动的报异常:
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):java.lang.RuntimeException:UnabletoinstantiateactivityComponentInfo{com.archer.rainbow/com.archer.rainbow.MyServiceActivity}:java.lang.NullPointerException
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.app.ActivityThread.performLaunchActivity(ActivityThread.java:1570)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1664)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.app.ActivityThread.access$1600(ActivityThread.java:118)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.app.ActivityThread$H.handleMessage(ActivityThread.java:949)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.os.Handler.dispatchMessage(Handler.java:99)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.os.Looper.loop(Looper.java:130)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.app.ActivityThread.main(ActivityThread.java:3711)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atjava.lang.reflect.Method.invokeNative(NativeMethod)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atjava.lang.reflect.Method.invoke(Method.java:507)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atcom.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atcom.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atdalvik.system.NativeStart.main(NativeMethod)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):Causedby:java.lang.NullPointerException
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.content.ContextWrapper.getPackageName(ContextWrapper.java:120)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.content.ComponentName.<init>(ComponentName.java:75)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.content.Intent.<init>(Intent.java:2936)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atcom.archer.rainbow.MyServiceActivity$1.<init>(MyServiceActivity.java:40)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atcom.archer.rainbow.MyServiceActivity.<init>(MyServiceActivity.java:38)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atjava.lang.Class.newInstanceImpl(NativeMethod)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atjava.lang.Class.newInstance(Class.java:1409)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.app.Instrumentation.newActivity(Instrumentation.java:1021)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):atandroid.app.ActivityThread.performLaunchActivity(ActivityThread.java:1562)
- 08-0812:03:22.894:ERROR/AndroidRuntime(2662):...11more
一开始,我还以为是我的哪个变量没有初始化呢,结果,看来看去,一共没几个变量啊,而且都应该正常赋值了,所以就很是纳闷了。但这个问题不解决不行啊,所以我就在一EOE论坛里发贴求高手解答。虽然有几个热心的网友帮忙给了些建议,但都不奏效啊。没办法,自己再想吧。后来,我换了一种写法:
- privatefinalIntentintent=newIntent();
- intent.setComponent(newComponentName(MyServiceActivity.this.getPackageName(),MyService.class.toString()));
并在第二句打了个断点进行了DEBUG,按F5进去之后发现:
- publicStringgetPackageName(){
- returnmBase.getPackageName();
- }
中的 mBase 竟然为 null ,无语了。这个方法可是ContextWrapper里的啊,Activity继承自它,怎么会没有传这个值给它呢?后来发现,Activity在OnCreate之前进行init的时候,调用了
- publicContextWrapper(Contextbase){
- mBase=base;
- }
此时,传进去的 base 即为 null,所以这样一来,便出现上面的问题。
为了避免这样的问题,需要在Activity在执行到onCreate()方法之后(包括在onCreate()方法),对该Intent进行赋值即可。
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- startSer1=(Button)findViewById(R.id.startSer1);
- stopSer1=(Button)findViewById(R.id.stopSer1);
- startSer2=(Button)findViewById(R.id.startSer2);
- stopSer2=(Button)findViewById(R.id.stopSer2);
- log=(TextView)findViewById(R.id.log);
- startSer1.setOnClickListener(btnListener);
- stopSer1.setOnClickListener(btnListener);
- startSer2.setOnClickListener(btnListener);
- stopSer2.setOnClickListener(btnListener);
- intent=newIntent(MyServiceActivity.this,MyService.class);
- }
通过这个Demo,吸取到了一个教训:需要使用Context方面的信息,最好在onCreate()方法之后(包括之)。
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