java – Android – 活动构造函数

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我注意到使用快捷键Alt Insert并选择构建器,它尝试使用每个私有属性(例如cManager和mTextView)创建构造函数.我记得我已经创建了没有它的项目并且工作正常.

在完整的logcat和Activity构造函数之后运行应用程序时发生错误：

具有私有财产的构造函数：

private ConnectivityManager cManager;
private TextView mTextView;

public SplashScreenActivity() {
    this.cManager = (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
    this.mTextView = (TextView)this.findViewById(R.id.mProgressText);
}

logcat的：

02-20 18:20:56.155    1591-1591/com.universo91.towersrock I/art﹕ Not late-enabling -Xcheck:jni (already on)
02-20 18:20:58.355    1591-1591/com.universo91.towersrock D/AndroidRuntime﹕ Shutting down VM
    --------- beginning of crash
02-20 18:20:58.361    1591-1591/com.universo91.towersrock E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.universo91.towersrock, PID: 1591
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.universo91.towersrock/com.universo91.towersrock.Pages.SplashScreenActivity}: java.lang.InstantiationException: class com.universo91.towersrock.Pages.SplashScreenActivity has no zero argument constructor
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.InstantiationException: class com.universo91.towersrock.Pages.SplashScreenActivity has no zero argument constructor
            at java.lang.Class.newInstance(Class.java:1563)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NoSuchMethodException: <init> []
            at java.lang.Class.getConstructor(Class.java:531)
            at java.lang.Class.getDeclaredConstructor(Class.java:510)
            at java.lang.Class.newInstance(Class.java:1561)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
02-20 18:20:58.772    1591-1603/com.universo91.towersrock I/art﹕ Background sticky concurrent mark sweep GC freed 1747(114KB) AllocSpace objects, 0(0B) LOS objects, 37% free, 391KB/623KB, paused 825us total 382.655ms
02-20 18:21:29.824    1690-1690/com.universo91.towersrock D/AndroidRuntime﹕ Shutting down VM
02-20 18:21:29.829    1690-1690/com.universo91.towersrock E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.universo91.towersrock, PID: 1690
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.universo91.towersrock/com.universo91.towersrock.Pages.SplashScreenActivity}: java.lang.InstantiationException: class com.universo91.towersrock.Pages.SplashScreenActivity has no zero argument constructor
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.InstantiationException: class com.universo91.towersrock.Pages.SplashScreenActivity has no zero argument constructor
            at java.lang.Class.newInstance(Class.java:1563)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NoSuchMethodException: <init> []
            at java.lang.Class.getConstructor(Class.java:531)
            at java.lang.Class.getDeclaredConstructor(Class.java:510)
            at java.lang.Class.newInstance(Class.java:1561)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
02-20 18:21:30.168    1690-1702/com.universo91.towersrock I/art﹕ Background sticky concurrent mark sweep GC freed 1749(114KB) AllocSpace objects, 0(0B) LOS objects, 37% free, 391KB/623KB, paused 856us total 166.355ms
02-20 18:21:53.341    1690-1690/com.universo91.towersrock I/Process﹕ Sending signal. PID: 1690 SIG: 9
02-20 18:26:00.878    1754-1754/com.universo91.towersrock D/AndroidRuntime﹕ Shutting down VM
02-20 18:26:00.903    1754-1754/com.universo91.towersrock E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.universo91.towersrock, PID: 1754
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.universo91.towersrock/com.universo91.towersrock.Pages.SplashScreenActivity}: java.lang.IllegalStateException: System services not available to Activities before onCreate()
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
            at android.app.Activity.getSystemService(Activity.java:4989)
            at com.universo91.towersrock.Pages.SplashScreenActivity.<init>(SplashScreenActivity.java:24)
            at java.lang.reflect.Constructor.newInstance(Native Method)
            at java.lang.Class.newInstance(Class.java:1572)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
02-20 18:26:01.144    1754-1766/com.universo91.towersrock I/art﹕ Background sticky concurrent mark sweep GC freed 1745(118KB) AllocSpace objects, 0(0B) LOS objects, 38% free, 382KB/623KB, paused 950us total 131.218ms
02-20 18:26:04.429    1754-1754/com.universo91.towersrock I/Process﹕ Sending signal. PID: 1754 SIG: 9

解决方法:

所有初始化都应该在Activity的onCreate()方法中执行：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.cManager = (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
    this.mTextView = (TextView)this.findViewById(R.id.mProgressText);
}

覆盖Activity的构造函数需要相当多的繁重工作,并且真的不是在公园散步.虽然你[当然]可以为Activity创建一个空的构造函数,但在Android框架的上下文中它确实是多余的.

相关答案：

1. Why I cannot pass parameters to Android Activity Constructor.

2. Start an Activity with a parameter.

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