这是什么错误，应用程序崩溃

这里是主要活动代码................................. .................................................. ...................这是什么错误，应用程序崩溃

package com.josephvarkey996gmail.test1; 
    import android.content.Intent; 
    import android.os.Bundle; 
    import android.support.v7.app.AppCompatActivity; 
    import android.util.Log; 
    import android.view.Menu; 
    import android.view.MenuItem; 
    import android.view.View; 
    import android.widget.ImageButton; 

    import com.parse.ParseAnalytics; 
    import com.parse.ParseUser; 

    public abstract class MainActivity extends AppCompatActivity { 

     public static final String TAG = MainActivity.class.getSimpleName(); 
    public ImageButton imgbutton; 
     protected void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.activity_main); 

      ParseAnalytics.trackAppOpenedInBackground(getIntent()); 


      ParseUser currentUser = ParseUser.getCurrentUser(); 
      if(currentUser==null) { 
       navigatetologin(); 
      } 
      if(currentUser!=null) 
      { 
       Log.i(TAG ,currentUser.getUsername()); 


      } 
      // Enable Local Datastore. 
    imgbutton= (ImageButton)findViewById(R.id.frnd); 
      imgbutton.setOnClickListener(new View.OnClickListener() { 
       @Override 
       public void onClick(View v) { 
        Intent intent = new Intent(MainActivity.this, Editfriends.class); 
        startActivity(intent); 
       } 
      }); 

     } 

     @Override 
     public boolean onCreateOptionsMenu(Menu menu) { 
      // Inflate the menu; this adds items to the action bar if it is present. 
      getMenuInflater().inflate(R.menu.menu_main, menu); 
      return true; 
     } 

     @Override 
     public boolean onOptionsItemSelected(MenuItem item) { 
      // Handle action bar item clicks here. The action bar will 
      // automatically handle clicks on the Home/Up button, so long 
      // as you specify a parent activity in AndroidManifest.xml. 
      int id = item.getItemId(); 

      //noinspection SimplifiableIfStatement 
      if (id == R.id.action_logout) { 
       ParseUser.logOut(); 
       navigatetologin(); 
      } 
      else if (id==R.id.action_edit_friends){ 
       Intent intent = new Intent(this, Editfriends.class); 
       intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
       intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK); 
       startActivity(intent); 
      } 

      return super.onOptionsItemSelected(item); 
     } 

     private void navigatetologin() { 
      Intent intent = new Intent(this, LoginActivity.class); 
      intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
      intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK); 
      startActivity(intent); 
     } 
    }

这里是Editfriend活动................... ......

package com.josephvarkey996gmail.test1; 

import android.app.ListActivity; 
import android.os.Bundle; 
import android.support.v7.app.AlertDialog; 
import android.util.Log; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.Window; 
import android.widget.ArrayAdapter; 

import com.parse.FindCallback; 
import com.parse.ParseException; 
import com.parse.ParseQuery; 
import com.parse.ParseUser; 

import java.util.List; 


public class Editfriends extends ListActivity { 
public static final String Tag=Editfriends.class.getSimpleName(); 
    protected List<ParseUser> mUser; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS); 
     setContentView(R.layout.activity_editfriends); 
    } 

    @Override 
    protected void onResume() { 
     super.onResume(); 
     setProgressBarIndeterminateVisibility(true); 
     ParseQuery<ParseUser> query= ParseUser.getQuery(); 
     query.orderByAscending(ParseConstants.key_Username); 
     query.setLimit(1000); 
     query.findInBackground(new FindCallback<ParseUser>() { 
      @Override 
      public void done(List<ParseUser> users, ParseException e) { 
       setProgressBarIndeterminateVisibility(true); 
       if (e== null){ 
         mUser=users; 
        String[] username = new String[mUser.size()]; 
        int i=0; 
        for(ParseUser user:mUser){ 
         username[i]=user.getUsername(); 
         i++; 
        } 
        ArrayAdapter<String> adapter = new ArrayAdapter<>(Editfriends.this,android.R.layout.simple_list_item_checked,username); 
        setListAdapter(adapter); 
       } 
       else 
       { 
        Log.e(Tag,e.getMessage()); 
        AlertDialog.Builder builder=new AlertDialog.Builder(Editfriends.this); 
        builder.setMessage(e.getMessage()).setTitle(R.string.error_title).setPositiveButton(android.R.string.ok, null); 
        AlertDialog dialog = builder.create(); 
        dialog.show(); 
       } 
      } 
     }); 

    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_editfriends, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 
}

这里是logcat的，即时通讯新手。所以不能理解笏它说，在logcat的 .................... ...

Process: com.josephvarkey996gmail.test1, PID: 2736 
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.josephvarkey996gmail.test1/com.josephvarkey996gmail.test1.MainActivity}: java.lang.InstantiationException: class com.josephvarkey996gmail.test1.MainActivity cannot be instantiated 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2236) 
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
      at android.app.ActivityThread.access$800(ActivityThread.java:151) 
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
      at android.os.Handler.dispatchMessage(Handler.java:102) 
      at android.os.Looper.loop(Looper.java:135) 
      at android.app.ActivityThread.main(ActivityThread.java:5257) 
      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:903) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
    Caused by: java.lang.InstantiationException: class com.josephvarkey996gmail.test1.MainActivity cannot be instantiated 
      at java.lang.Class.newInstance(Class.java:1587) 
      at android.app.Instrumentation.newActivity(Instrumentation.java:1066) 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2226) 
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390) 
            at android.app.ActivityThread.access$800(ActivityThread.java:151) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
            at android.os.Handler.dispatchMessage(Handler.java:102) 
            at android.os.Looper.loop(Looper.java:135) 
            at android.app.ActivityThread.main(ActivityThread.java:5257) 
            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:903) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
07-21 18:23:09.419 2736-2748/com.josephvarkey996gmail.test1 I/art﹕ Background sticky concurrent mark sweep GC freed 3678(165KB) AllocSpace objects, 0(0B) LOS objects, 0% free, 1170KB/1170KB, paused 7.592ms total 95.745ms

来源

2015-07-21 Joseph Varkey

您必须删除抽象的修改。 – krystian71115

抽象类不能被实例化。查看文档：https：//docs.oracle.com/javase/tutorial/java/IandI/abstract.html – krystian71115

public ** abstract ** class MainActivity extends AppCompatActivity'为什么在地球上你需要MainActivity是抽象的！！ – Kedarnath

变化

public abstract class MainActivity extends AppCompatActivity

到

public class MainActivity extends AppCompatActivity

来源

2015-07-21 13:16:38 Soham

MainActivity是abstract class。所以你需要扩展这个类或删除抽象声明。

抽象Java编程语言包括创建一个或多个接口或抽象类隐藏实现细节。

扩展抽象类：

public class MainActivity2 extends MainActivity { 

    protected void onCreate(Bundle savedInstanceState) { 
     //This calls the superclass method: MainActivity onCreate 
     super.onCreate(savedInstanceState); 
    } 
}

删除抽象类：

public class MainActivity extends AppCompatActivity { 

    public void onCreate(Bundle savedInstanceState) { 
     setContentView(R.layout.activity_main); 
     ... 
    } 
}

来源

2015-07-21 13:25:09 heloisasim

谢谢@heloisasim，它显示主要活动，但现在它显示另一个错误，当我去Editfriends activity.please可以看看logcat。 –

@JosephVarkey首先，请接受一个正确的答案，然后发布另一个问题。我建议你多读一点关于android（activity的生命周期）的内容。 – heloisasim

这是什么错误，应用程序崩溃

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