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这里是活动课和第二活动课。按钮显示空指针异常，第二个类不起作用。这里是活动类和第二个活动类。按钮不工作的第二个类显示空指针异常

FirstActivity.java 中的 showevent()

public void ShowEvent(View view){
        Intent intent = new Intent(this, Getclicker.class);
         date = (TextView)findViewById(R.id.textView2);
        String datevalue = date.getText().toString();
        userSelection=(TextView)findViewById(R.id.textView1);
        String Userselectvalue = userSelection.getText().toString();

        intent.putExtra(EXTRA_MESSAGE, datevalue);
        intent.putExtra(EXTRA_MESSAGE1, Userselectvalue);

        startActivity(intent);
    }

Getclicker.java

package example.events1;

import android.app.ListActivity;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;
import android.widget.ListView;

public class Getclicker  extends ListActivity {

    classdbOpenHelper eventsData1;
    Cursor cursor1;
     ListView listView ; 

    @Override
    public void onCreate(Bundle savedInstanceState) {
        Intent intent = getIntent();
        String datevalue = intent.getStringExtra(FirstActivity.EXTRA_MESSAGE);
        String Userselectvalue = intent.getStringExtra(FirstActivity.EXTRA_MESSAGE1);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);                       /*String datevalue = date.getText().toString();
        String Userselectvalue = userSelection.getText().toString();

        String showevent = eventsData.getContact(datevalue,Userselectvalue);
        show.setText(showevent);*/

         cursor1 = eventsData1.getContact(datevalue,Userselectvalue);
         String[] fromColumns = {classdbOpenHelper.KEY_EVENT};
         int[] toViews = {R.id.event};
         SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,R.layout.events, cursor1, fromColumns, toViews,0 );
          listView = (ListView) findViewById(R.id.list); 
         listView.setAdapter(adapter);
        }

    public void onDestroy() {
        eventsData1.close();
      }

}

日志猫

 08-07 11:40:40.795: E/AndroidRuntime(2544): FATAL EXCEPTION: main
08-07 11:40:40.795: E/AndroidRuntime(2544): java.lang.RuntimeException: Unable to start activity ComponentInfo{example.events1/example.events1.Getclicker}: java.lang.NullPointerException
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.os.Looper.loop(Looper.java:137)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.app.ActivityThread.main(ActivityThread.java:5041)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at java.lang.reflect.Method.invokeNative(Native Method)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at java.lang.reflect.Method.invoke(Method.java:511)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at dalvik.system.NativeStart.main(Native Method)
08-07 11:40:40.795: E/AndroidRuntime(2544): Caused by: java.lang.NullPointerException
08-07 11:40:40.795: E/AndroidRuntime(2544):     at example.events1.Getclicker.onCreate(Getclicker.java:28)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.app.Activity.performCreate(Activity.java:5104)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
08-07 11:40:40.795: E/AndroidRuntime(2544):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
08-07 11:40:40.795: E/AndroidRuntime(2544):     ... 11 more
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1 回答 1

1

您的代码中的问题在这里

    cursor1 = eventsData1.getContact(datevalue,Userselectvalue);

eventData1 未初始化为任何内容。

于 2013-08-07T12:05:26.297 回答