Android 不保存 TextInputEditText 的状态

Question

So I previously asked a question titled " Switching from Fragment A to Fragment B with navigation drawer, stops Fragment A from working " After doing a lot of research I realised I wasn't even attempting to save the state of the fragment. After troubleshooting all day I still don't have it so came back for wisdom on how to solve this. Like I said in my previous question, I'm new so don't quite get it all so hopefully not embarrassing myself too much.

For context, the app is a language translation app, you enter the text, hit the button translate , and read the result. When switching fragments, ie Home to Gallery then back to Home , the translation and text input is gone.

Simply, why is my text not being saved when switching?

The onCreate code I have is:

  @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if(savedInstanceState != null)
        {
            sourceEdit.setText(savedInstanceState.getString("textKey"));

        }

The onSaveInstanceState:

 @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("textKey", sourceEdit.getText().toString());
    }

The full code just incase:

public class MainDrawerActivity extends AppCompatActivity {

    private AppBarConfiguration mAppBarConfiguration;
    private ActivityMainDrawerBinding binding;
    private Spinner fromSpinner, toSpinner;
    private TextInputEditText sourceEdit;
    private ImageView micIV;
    private MaterialButton translateBtn;
    private TextView translatedTV;
    String[] fromLanguages = {"From","English","Korean"};
    String[] toLanguages = {"From","English","Korean"};


    private static final int REQUEST_PERMISSION_CODE = 1;
    int languageCode, fromLanguageCode, toLanguageCode = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if(savedInstanceState != null)
        {
            sourceEdit.setText(savedInstanceState.getString("textKey"));

        }

        binding = ActivityMainDrawerBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());

        setSupportActionBar(binding.appBarMainDrawer.toolbar);

        DrawerLayout drawer = binding.drawerLayout;
        NavigationView navigationView = binding.navView;
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        mAppBarConfiguration = new AppBarConfiguration.Builder(
                R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow)
                .setOpenableLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_content_main_drawer);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);

        //start of language code

        fromSpinner = findViewById(R.id.idFromSpinner);
        toSpinner = findViewById(R.id.idToSpinner);
        sourceEdit = findViewById(R.id.idEditSource);
        micIV = findViewById(R.id.idIVMic);
        translateBtn = findViewById(R.id.idButtonTranslate);
        translatedTV = findViewById(R.id.idTVTranslatedTV);

        fromSpinner.setOnItemSelectedListener(new OnItemSelectedListener(){
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                fromLanguageCode = getLanguageCode(fromLanguages[position]);
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });

        ArrayAdapter fromAdapter = new ArrayAdapter(this, R.layout.spinner_item, fromLanguages);
        fromAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        fromSpinner.setAdapter(fromAdapter);

        toSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                toLanguageCode = getLanguageCode(toLanguages[position]);
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });

        ArrayAdapter toAdapter = new ArrayAdapter(this,R.layout.spinner_item, toLanguages);
        toAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        toSpinner.setAdapter(toAdapter);

        translateBtn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                translatedTV.setText("");
                if(sourceEdit.getText().toString().isEmpty()){
                    makeText(MainDrawerActivity.this, "Please enter text", Toast.LENGTH_SHORT).show();
                }
                else if(fromLanguageCode==0){
                    makeText(MainDrawerActivity.this, "Please select source language", Toast.LENGTH_SHORT).show();
                }
                else if(toLanguageCode==0){
                    makeText(MainDrawerActivity.this, "Please select language to translate too", Toast.LENGTH_SHORT).show();
                } else {
                    translateText(fromLanguageCode, toLanguageCode, sourceEdit.getText().toString());

                }
                InputMethodManager inputManager = (InputMethodManager)
                        getSystemService(Context.INPUT_METHOD_SERVICE);

                inputManager.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(),
                        InputMethodManager.HIDE_NOT_ALWAYS);
            }
        });

        micIV.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent i = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
                i.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL,RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
                i.putExtra(RecognizerIntent.EXTRA_LANGUAGE, Locale.getDefault());
                i.putExtra(RecognizerIntent.EXTRA_PROMPT,"Speak to translate text");
                try {
                    startActivityForResult(i, REQUEST_PERMISSION_CODE);
                } catch (Exception e){
                    e.printStackTrace();
                    Toast.makeText(MainDrawerActivity.this, " "+e.getMessage(), Toast.LENGTH_SHORT).show();
                }

            }
        });
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("textKey", sourceEdit.getText().toString());
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(requestCode==REQUEST_PERMISSION_CODE){
            if(resultCode==RESULT_OK && data!=null){
                ArrayList<String> result = data.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS);
                sourceEdit.setText(result.get(0));
            }
        }
    }
    private void translateText(int fromLanguageCode, int toLanguageCode, String source) {
        translatedTV.setText("Downloading Model...");
        FirebaseTranslatorOptions options = new FirebaseTranslatorOptions.Builder()
                .setSourceLanguage(fromLanguageCode)
                .setTargetLanguage(toLanguageCode)
                .build();
        FirebaseTranslator translator = FirebaseNaturalLanguage.getInstance().getTranslator(options);

        FirebaseModelDownloadConditions conditions = new FirebaseModelDownloadConditions.Builder().build();

        translator.downloadModelIfNeeded(conditions).addOnSuccessListener(new OnSuccessListener<Void>() {
            @Override
            public void onSuccess(Void unused) {
                translatedTV.setText("Translating...");
                translator.translate(source).addOnSuccessListener(new OnSuccessListener<String>() {
                    @Override
                    public void onSuccess(String s) {
                        translatedTV.setText(s);
                    }
                }).addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        Toast.makeText(MainDrawerActivity.this, "Failed to translate: " + e.getMessage(), Toast.LENGTH_SHORT).show();
                    }
                });
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Toast.makeText(MainDrawerActivity.this, "Failed to download model... " + e.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
    }

    //Method that gets the languages from Firebase
    public int getLanguageCode(String language) {
        int languageCode = 0;
        switch (language) {
            case "English":
                languageCode = FirebaseTranslateLanguage.EN;
                break;
            case "Korean":
                languageCode = FirebaseTranslateLanguage.KO;
                break;
            default:
                languageCode = 0;
        }
        return languageCode;
    }


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

    @Override
    public boolean onSupportNavigateUp() {
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_content_main_drawer);
        return NavigationUI.navigateUp(navController, mAppBarConfiguration)
                || super.onSupportNavigateUp();
    }
}

Answer 1

  @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if(savedInstanceState != null)
        {
            sourceEdit.setText(savedInstanceState.getString("textKey"));

        }

If this happening in fragment. UI isn't created yet. So you have to save in some variable.

String myEditString;
  @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if(savedInstanceState != null)
        {
            myEditString = savedInstanceState.getString("textKey");

        }

And than in onViewCrated() do your insertion and you have to do that in you fragments. Or just use ViewModel class from jetpack
ok i see you code from activity. you isnt initialized your sourceEdit when trying to access it. And if uou using bindings you dont have to save all your UI in variavles. It will hold them all just use binding.yourIdInXml