Controlar el “botón” de nuevo en Android

StackOverflow https://stackoverflow.com/questions/1265095

  •  13-09-2019
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Pregunta

Quiero conseguir el valor de datos de texto desde la Sub-Actividad espalda. Y todo está bien. Pero cuando se abrió la Sub-actividad, entonces simplemente haga clic en Atrás "botón" en el teléfono, se lanza un error de excepción. He encontrado en la toturial el control del ciclo de vida Bloc de notas androide, pero es difícil de entender. ¿Alguien me puede ayudar? Este es mi código: 

public class SBooks extends ListActivity {
private String title_raw;
private SBooksDbAdapter mDbHelper;  
private static final int ACTIVITY_SEARCH = 0;   

private static final int SEARCH_ID = Menu.FIRST;     

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.sbooks_list);       
    mDbHelper = new SBooksDbAdapter(this);
    mDbHelper.open();                    

}

// Create Menu Option
@Override
public boolean onCreateOptionsMenu(Menu menu) {        
    boolean result = super.onCreateOptionsMenu(menu);
    menu.add(0, SEARCH_ID, 0, R.string.menu_search);            
    return result;      
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch(item.getItemId()){
    case SEARCH_ID:
        Intent intent = new Intent(this, SBooksSearch.class);
        startActivityForResult(intent, ACTIVITY_SEARCH);            

    return super.onOptionsItemSelected(item);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent){
    super.onActivityResult(requestCode, resultCode, intent);
        switch(requestCode){
        case ACTIVITY_SEARCH:
            Bundle bundle = intent.getExtras();
            title_raw = bundle.getString(SBooksDbAdapter.KEY_TITLE_RAW);
            if(title_raw!=null){
                Cursor cursor = mDbHelper.searchData(title_raw);
                String[] from = new String[]{ SBooksDbAdapter.KEY_ROWID,
                        SBooksDbAdapter.KEY_TITLE, SBooksDbAdapter.KEY_LYRICS };
                int[] to = new int[]{ R.id.id, R.id.title, R.id.lyrics };
                SimpleCursorAdapter adapter = 
                    new SimpleCursorAdapter(this, R.layout.sbooks_row, cursor, from, to );
                setListAdapter(adapter);

        }

    }   
}

}

Esta es mi Sub-Actividad: 

public class SBooksSearch extends Activity {
private EditText mTextSearch;
private Button searchButton;
private SBooksDbAdapter mDbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);     
    setContentView(R.layout.sbooks_search); 

    mTextSearch = (EditText)findViewById(R.id.text_search);     
    searchButton = (Button)findViewById(R.id.btn_search);       

    searchButton.setOnClickListener(new View.OnClickListener(){
        public void onClick(View v){                
            Intent intent = new Intent();
            intent.putExtra(SBooksDbAdapter.KEY_TITLE_RAW, mTextSearch.getText().toString());               
            setResult(RESULT_OK, intent);
            finish();

        }
    });
}   

@Override
protected void onSaveInstanceState(Bundle outState){
    super.onSaveInstanceState(outState);

}
@Override
protected void onPause(){
    super.onPause();
    checkState();

}
@Override
protected void onResume(){
    super.onResume();       
}


private void checkState() {     

} }

Este es Logcat: 

08-12 18:44:39.211: WARN/InputManagerService(581): Starting input on non-focused client com.android.internal.view.IInputMethodClient$Stub$Proxy@43719140 (uid=10004 pid=623)
08-12 18:44:39.510: INFO/ActivityManager(581): Displayed activity com.original.sbooks/.SBooks: 4934 ms
08-12 18:44:40.821: WARN/KeyCharacterMap(730): No keyboard for id 0
08-12 18:44:40.821: WARN/KeyCharacterMap(730): Using default keymap: /system/usr/keychars/qwerty.kcm.bin
08-12 18:44:41.412: INFO/ARMAssembler(581): generated scanline__00000177:03515104_00001A01_00000000 [ 64 ipp] (89 ins) at [0x297608:0x29776c] in 952924 ns
08-12 18:44:41.520: INFO/ARMAssembler(581): generated scanline__00000177:03515104_00000A01_00000000 [ 46 ipp] (70 ins) at [0x297798:0x2978b0] in 517061 ns
08-12 18:44:42.171: INFO/ActivityManager(581): Starting activity: Intent { comp={com.original.sbooks/com.original.sbooks.SBooksSearch} }
08-12 18:44:52.196: WARN/ActivityManager(581): Launch timeout has expired, giving up wake lock!
08-12 18:44:52.279: WARN/ActivityManager(581): Activity idle timeout for HistoryRecord{436bfc80 {com.original.sbooks/com.original.sbooks.SBooksSearch}}
08-12 18:44:57.350: DEBUG/dalvikvm(620): GC freed 4103 objects / 231808 bytes in 75ms
08-12 18:45:05.130: DEBUG/dalvikvm(649): GC freed 2604 objects / 150112 bytes in 88ms
08-12 18:45:10.120: DEBUG/dalvikvm(623): GC freed 2750 objects / 149592 bytes in 71ms
08-12 18:45:11.920: INFO/ActivityManager(581): Displayed activity com.original.sbooks/.SBooksSearch: 29748 ms
08-12 18:45:17.263: WARN/ActivityManager(581): Activity pause timeout for HistoryRecord{436bfc80 {com.original.sbooks/com.original.sbooks.SBooksSearch}}
08-12 18:45:26.762: WARN/ActivityManager(581): Launch timeout has expired, giving up wake lock!
08-12 18:45:27.272: WARN/ActivityManager(581): Activity idle timeout for HistoryRecord{435a7760 {com.original.sbooks/com.original.sbooks.SBooks}}
08-12 18:46:04.905: DEBUG/AndroidRuntime(730): Shutting down VM
08-12 18:46:04.905: WARN/dalvikvm(730): threadid=3: thread exiting with uncaught exception (group=0x4000fe70)
08-12 18:46:04.905: ERROR/AndroidRuntime(730): Uncaught handler: thread main exiting due to uncaught exception
08-12 18:46:04.991: ERROR/AndroidRuntime(730): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=0, result=0, data=null} to activity {com.original.sbooks/com.original.sbooks.SBooks}: java.lang.NullPointerException
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.app.ActivityThread.deliverResults(ActivityThread.java:3005)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.app.ActivityThread.handleSendResult(ActivityThread.java:3047)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.app.ActivityThread.access$2300(ActivityThread.java:112)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1721)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.os.Looper.loop(Looper.java:123)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.app.ActivityThread.main(ActivityThread.java:3948)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at java.lang.reflect.Method.invokeNative(Native Method)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at java.lang.reflect.Method.invoke(Method.java:521)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:782)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:540)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at dalvik.system.NativeStart.main(Native Method)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): Caused by: java.lang.NullPointerException
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at com.original.sbooks.SBooks.onActivityResult(SBooks.java:111)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.app.Activity.dispatchActivityResult(Activity.java:3595)
08-12 18:46:04.991: ERROR/AndroidRuntime(730):     at android.app.ActivityThread.deliverResults(ActivityThread.java:3001)
¿Fue útil?

Solución

Creo que Nate es correcta acerca de la NPE en intent.getExtras ().

Se debe comprobar el valor de su código de resultado antes de hacer nada. También puede ser que desee comprobar para asegurarse de intent.hasExtra (SBooksDbAdapter.KEY_TITLE_RAW) antes de llegar a ese valor. Por lo tanto, algo como esto: 

switch(requestCode){
case ACTIVITY_SEARCH:
    if (resultCode == RESULT_OK && intent.hasExtra(SBooksDbAdapter.KEY_TITLE_RAW)) {
        title_raw = intent.getStringExtra(SBooksDbAdapter.KEY_TITLE_RAW);
        ... do all that other stuff ...
    }
}

Otros consejos

Trate de poner en algún registro en el método de su actividad onActivityResult (...). El botón "atrás" de la subactividad puede estar dando un código de resultado de RESULT_CANCELED, y la intención puede ser nulo en ese caso. Así se logra un NPE a

Bundle haz = intent.getExtras ();

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