java - 在 Android Fragment 中实现 Back Pressed

Question

我陷入了困境，需要一些帮助。这里有很多关于这个主题的文章，但没有一篇回答我的问题。我想在 fragments 中实现 onBackPressed()并显示dialog显示是否退出应用程序的框。任何帮助将不胜感激。

LoginFragment.java

    public class LoginFragment extends Fragment {
    public static final String TAG = LoginFragment.class.getSimpleName();

    private EditText mEtEmail;
    private EditText mEtPassword;
    private Button mBtLogin;
    private TextView mTvRegister;
    private TextView mTvForgotPassword;
    private TextInputLayout mTiEmail;
    private TextInputLayout mTiPassword;
    private ProgressBar mProgressBar;

    private CompositeSubscription mSubscriptions;
    private SharedPreferences mSharedPreferences;

    @NonNull
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_login,container,false);
        mSubscriptions = new CompositeSubscription();
        initViews(view);
        initSharedPreferences();
        return view;
    }
    private void initViews(View v) {

        mEtEmail = v.findViewById(R.id.et_email);
        mEtPassword = v.findViewById(R.id.et_password);
        mBtLogin = v.findViewById(R.id.btn_login);
        mTiEmail = v.findViewById(R.id.ti_email);
        mTiPassword = v.findViewById(R.id.ti_password);
        mProgressBar = v.findViewById(R.id.progress);
        mTvRegister = v.findViewById(R.id.tv_register);
        mTvForgotPassword = v.findViewById(R.id.tv_forgot_password);

        mBtLogin.setOnClickListener(view -> login());
        mTvRegister.setOnClickListener(view -> goToRegister());
        mTvForgotPassword.setOnClickListener(view -> showDialog());
    }

    private void initSharedPreferences() {

        mSharedPreferences = PreferenceManager.getDefaultSharedPreferences(getActivity());
    }

    private void login() {

        setError();

        String email = mEtEmail.getText().toString();
        String password = mEtPassword.getText().toString();

        int err = 0;

        if (!validateEmail(email)) {

            err++;
            mTiEmail.setError("Email should be valid !");
        }

        if (!validateFields(password)) {

            err++;
            mTiPassword.setError("Password should not be empty !");
        }

        if (err == 0) {

            loginProcess(email,password);
            mProgressBar.setVisibility(View.VISIBLE);

        } else {

            showSnackBarMessage("Enter Valid Details !");
        }
    }

    private void setError() {

        mTiEmail.setError(null);
        mTiPassword.setError(null);
    }

    private void loginProcess(String email, String password) {

        mSubscriptions.add(NetworkUtil.getRetrofit(email, password).login()
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io())
                .subscribe(this::handleResponse,this::handleError));
    }

    private void handleResponse(Response response) {

        mProgressBar.setVisibility(View.GONE);

        SharedPreferences.Editor editor = mSharedPreferences.edit();
        editor.putString(Constants.TOKEN,response.getToken());
        editor.putString(Constants.EMAIL,response.getMessage());
        editor.apply();

        mEtEmail.setText(null);
        mEtPassword.setText(null);

        Intent intent = new Intent(getActivity(),  HomeActivity.class);
        startActivity(intent);

    }

    private void handleError(Throwable error) {

        mProgressBar.setVisibility(View.GONE);

        if (error instanceof HttpException) {

            Gson gson = new GsonBuilder().create();

            try {

                String errorBody = ((HttpException) error).response().errorBody().string();
                Response response = gson.fromJson(errorBody,Response.class);
                showSnackBarMessage(response.getMessage());

            } catch (IOException e) {
                e.printStackTrace();
            }
        } else {

            showSnackBarMessage("No Internet Connection!");
        }
    }

    private void showSnackBarMessage(String message) {

        if (getView() != null) {

            Snackbar.make(getView(),message,Snackbar.LENGTH_SHORT).show();
        }
    }

    private void goToRegister(){

        FragmentTransaction ft = getFragmentManager().beginTransaction();
        RegisterFragment fragment = new RegisterFragment();
        ft.replace(R.id.fragmentFrame,fragment,RegisterFragment.TAG);
        ft.addToBackStack(null).commit();
    }

    private void showDialog(){

        ResetPasswordDialog fragment = new ResetPasswordDialog();

        fragment.show(getFragmentManager(), ResetPasswordDialog.TAG);
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        mSubscriptions.unsubscribe();
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity implements ResetPasswordDialog.Listener {

    public static final String TAG = MainActivity.class.getSimpleName();
    private LoginFragment mLoginFragment;
    private ResetPasswordDialog mResetPasswordDialog;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (savedInstanceState == null) {
            loadFragment();
        }
    }
    private void loadFragment() {

        if (mLoginFragment == null) {

            mLoginFragment = new LoginFragment();
        }
        getFragmentManager().beginTransaction().replace(R.id.fragmentFrame, mLoginFragment, LoginFragment.TAG).commit();
    }
    @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);

        String data = intent.getData().getLastPathSegment();
        Log.d(TAG, "onNewIntent: " + data);

        mResetPasswordDialog = (ResetPasswordDialog) getFragmentManager().findFragmentByTag(ResetPasswordDialog.TAG);

        if (mResetPasswordDialog != null)
            mResetPasswordDialog.setToken(data);
    }

    @Override
    public void onPasswordReset(String message) {

        showSnackBarMessage(message);
    }

    private void showSnackBarMessage(String message) {

        Snackbar.make(findViewById(R.id.activity_main), message, Snackbar.LENGTH_SHORT).show();

    }
}

在我的Login Fragment ，我想显示一个对话框“是否要退出应用程序”。上Yes它会消除当前 fragment 并结束 Activity ，否则它将保持 Activity 状态。请帮忙!

Answer 1

你甚至可以尝试这种方式

MainActivity.java

  @Override
public void onBackPressed() {

    if (getFragmentManager() != null && getFragmentManager().getBackStackEntryCount() >= 1) {

   String fragmentTag = getFragmentManager().findFragmentById(R.id.frame_container).getTag();

   if(fragmentTag.equals(LoginFragment.getTag())){
    // show Dialog code
      }else{
            super.onBackPressed();
      }

    } else {
         super.onBackPressed();
    }
}

在您的主 Activity 中添加此代码，以便当添加登录 fragment 并单击 backpress 时，首先如果该 fragment 被添加到 fragment 事务中，那么首先它会找到该 fragment 并检查其标签是否等于登录 fragment 标签。然后，如果两个标记都匹配，则您可以显示退出警报对话框。