Question

我是初学者，我只是想学习android方法的生命周期。这是我用过的简单代码。但这不起作用并给出致命的例外。此外，在我的手机上删除此应用程序后，它会出现错误Unfortunately Stopped activity。请帮忙！

MainActivity.java

package com.example.activity101;

import android.os.Bundle;
import android.app.Activity;
import android.util.Log;

public class MainActivity extends Activity {

String tag = "Lifecycle";

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d(tag, "In the onCreate() event");
}

public void onStart()
{
super.onStart();
Log.d(tag, "In the onStart() event");
}

public void onRestart() 
{
super.onRestart();
Log.d(tag,"In the OnResart() Event");
}

public void onResume()
{
super.onResume();
Log.d(tag, "In the onResume() event");
}
public void onPause()
{
super.onPause();
Log.d(tag, "In the onPause() event");
}

    public void onStop() {

    }
    {
    super.onStop();
    Log.d(tag, "In the onStop() event");
    }
    public void onDestroy()
    {
    super.onDestroy();
    Log.d(tag, "In the onDestroy() event");
    }

}

我的控制台错误：

07-09 11:48:17.512: I/Process(10035): Sending signal. PID: 10035 SIG: 9
07-09 11:49:07.257: D/AndroidRuntime(10595): Shutting down VM
07-09 11:49:07.257: W/dalvikvm(10595): threadid=1: thread exiting with uncaught exception (group=0x40d8e2a0)
07-09 11:49:07.262: E/AndroidRuntime(10595): FATAL EXCEPTION: main
07-09 11:49:07.262: E/AndroidRuntime(10595): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.activity101/com.example.activity101.MainActivity}: java.lang.NullPointerException
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2024)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.app.ActivityThread.access$600(ActivityThread.java:140)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.os.Looper.loop(Looper.java:137)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.app.ActivityThread.main(ActivityThread.java:4898)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at java.lang.reflect.Method.invokeNative(Native Method)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at java.lang.reflect.Method.invoke(Method.java:511)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1008)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:775)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at dalvik.system.NativeStart.main(Native Method)
07-09 11:49:07.262: E/AndroidRuntime(10595): Caused by: java.lang.NullPointerException
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.app.Activity.onStop(Activity.java:1403)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at com.example.activity101.MainActivity.<init>(MainActivity.java:45)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at java.lang.Class.newInstanceImpl(Native Method)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at java.lang.Class.newInstance(Class.java:1319)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.app.Instrumentation.newActivity(Instrumentation.java:1068)
07-09 11:49:07.262: E/AndroidRuntime(10595):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2015)
07-09 11:49:07.262: E/AndroidRuntime(10595):    ... 11 more
07-09 11:49:44.497: I/Process(10595): Sending signal. PID: 10595 SIG: 9

Answer 1

使用super.onStop();方法拨打onStop()，而不是外线：

public void onStop() {
 super.onStop();
 Log.d(tag, "In the onStop() event");
}

Answer 2

请执行以下操作 -

1） 在所有方法之前添加@Override。

2） 在每种方法中调用super。

<强> MainActivity.java

  package com.example.activity101;

  import android.os.Bundle;
  import android.app.Activity;
  import android.util.Log;

  public class MainActivity extends Activity {

  String tag = "Lifecycle";

  @Override
  public void onCreate(Bundle savedInstanceState) 
  {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      Log.d(tag, "In the onCreate() event");
  }

  @Override
  public void onStart()
  {
    super.onStart();
    Log.d(tag, "In the onStart() event");
  }

  @Override
  public void onRestart() 
  {
    super.onRestart();
    Log.d(tag,"In the OnResart() Event");
  }

  @Override
  public void onResume()
  {
    super.onResume();
    Log.d(tag, "In the onResume() event");
 }

  @Override
  public void onPause()
  {
    super.onPause();
    Log.d(tag, "In the onPause() event");
  }

  @Override
  public void onStop() 
  {
    super.onStop();
    Log.d(tag, "In the onStop() event");
  }

  @Override
  public void onDestroy()
  {
   super.onDestroy();
   Log.d(tag, "In the onDestroy() event");
  }
}

致命异常主要在android中

2 个答案: