android - 如何在 Android Studio 的登录 Activity 模板中实现 AsyncTask

Question

我想在我的 Android 应用程序中实现一个登录 Activity ，我使用 Android Studio 模板进行登录 Activity 。根据这里的谷歌文档:https://developer.android.com/studio/projects/templates#LoginActivity它应该包含一个 AsyncTask，我可以将其用于我的目的，但似乎当前版本的 Android Studio 不再提供此功能。

我当前使用的 android studio 版本是 3.4(2019 年 4 月 10 日)，我的 sdk 是:

        minSdkVersion 23
        targetSdkVersion 26

我有一个 LoginDataSource.java 类，其中包含我假设将用于身份验证工作的以下代码。但是，当我在 TODO 行下方调用我的 HTTP 方法时，它给了我一个关于无法在主线程中执行异步的异常:

/**
 * Class that handles authentication w/ login credentials and retrieves user information.
 */
public class LoginDataSource {

    public Result<LoggedInUser> login(String username, String password) {

        try {
            // TODO: handle loggedInUser authentication
            LoggedInUser fakeUser =
                    new LoggedInUser(
                            java.util.UUID.randomUUID().toString(),
                            "Jane Doe");
            return new Result.Success<>(fakeUser);
        } catch (Exception e) {
            return new Result.Error(new IOException("Error logging in", e));
        }
    }

    public void logout() {
        // TODO: revoke authentication
    }
}

我在之前的项目中使用 asynctask 实现了一个 HTTP 调用，但它是在使用它的同一个 Activity 中，而不是使用这个模板。放置异步任务并调用它的最佳位置应该在哪里？

谢谢!

模板中的其他类:

LoginRepository.java

/**
 * Class that requests authentication and user information from the remote data source and
 * maintains an in-memory cache of login status and user credentials information.
 */
public class LoginRepository {

    private static volatile LoginRepository instance;

    private LoginDataSource dataSource;

    // If user credentials will be cached in local storage, it is recommended it be encrypted
    // @see https://developer.android.com/training/articles/keystore
    private LoggedInUser user = null;

    // private constructor : singleton access
    private LoginRepository(LoginDataSource dataSource) {
        this.dataSource = dataSource;
    }

    public static LoginRepository getInstance(LoginDataSource dataSource) {
        if (instance == null) {
            instance = new LoginRepository(dataSource);
        }
        return instance;
    }

    public boolean isLoggedIn() {
        return user != null;
    }

    public void logout() {
        user = null;
        dataSource.logout();
    }

    private void setLoggedInUser(LoggedInUser user) {
        this.user = user;
        // If user credentials will be cached in local storage, it is recommended it be encrypted
        // @see https://developer.android.com/training/articles/keystore
    }

    public Result<LoggedInUser> login(String username, String password) {
        // handle login
        Result<LoggedInUser> result = dataSource.login(username, password);
        if (result instanceof Result.Success) {
            setLoggedInUser(((Result.Success<LoggedInUser>) result).getData());
        }
        return result;
    }
}

LoggedInUserView.java

/**
 * Class exposing authenticated user details to the UI.
 */
class LoggedInUserView implements Serializable {
    private String displayName;
    //... other data fields that may be accessible to the UI

    LoggedInUserView(String displayName) {
        this.displayName = displayName;
    }

    String getDisplayName() {
        return displayName;
    }
}

LoginViewModel.java

public class LoginViewModel extends ViewModel {

    private MutableLiveData<LoginFormState> loginFormState = new MutableLiveData<>();
    private MutableLiveData<LoginResult> loginResult = new MutableLiveData<>();
    private LoginRepository loginRepository;

    LoginViewModel(LoginRepository loginRepository) {
        this.loginRepository = loginRepository;
    }

    LiveData<LoginFormState> getLoginFormState() {
        return loginFormState;
    }

    LiveData<LoginResult> getLoginResult() {
        return loginResult;
    }

    public void login(String username, String password) {
        // can be launched in a separate asynchronous job
        Result<LoggedInUser> result = loginRepository.login(username, password);

        if (result instanceof Result.Success) {
            LoggedInUser data = ((Result.Success<LoggedInUser>) result).getData();
            loginResult.setValue(new LoginResult(new LoggedInUserView(data.getDisplayName())));
        } else {
            loginResult.setValue(new LoginResult(R.string.login_failed));
        }
    }

    public void loginDataChanged(String username, String password) {
        if (!isUserNameValid(username)) {
            loginFormState.setValue(new LoginFormState(R.string.invalid_username, null));
        } else if (!isPasswordValid(password)) {
            loginFormState.setValue(new LoginFormState(null, R.string.invalid_password));
        } else {
            loginFormState.setValue(new LoginFormState(true));
        }
    }

    // A placeholder username validation check
    private boolean isUserNameValid(String username) {
        if (username == null) {
            return false;
        }
        if (username.contains("@")) {
            return Patterns.EMAIL_ADDRESS.matcher(username).matches();
        } else {
            return !username.trim().isEmpty();
        }
    }

    // A placeholder password validation check
    private boolean isPasswordValid(String password) {
        return password != null && password.trim().length() > 5;
    }
}

LoginActivity.java

public class LoginActivity extends AppCompatActivity {

    private LoginViewModel loginViewModel;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        loginViewModel = ViewModelProviders.of(this, new LoginViewModelFactory())
                .get(LoginViewModel.class);

        final EditText usernameEditText = findViewById(R.id.username);
        final EditText passwordEditText = findViewById(R.id.password);
        final Button loginButton = findViewById(R.id.login);
        final ProgressBar loadingProgressBar = findViewById(R.id.loading);

        loginViewModel.getLoginFormState().observe(this, new Observer<LoginFormState>() {
            @Override
            public void onChanged(@Nullable LoginFormState loginFormState) {
                if (loginFormState == null) {
                    return;
                }
                loginButton.setEnabled(loginFormState.isDataValid());
                if (loginFormState.getUsernameError() != null) {
                    usernameEditText.setError(getString(loginFormState.getUsernameError()));
                }
                if (loginFormState.getPasswordError() != null) {
                    passwordEditText.setError(getString(loginFormState.getPasswordError()));
                }
            }
        });

        loginViewModel.getLoginResult().observe(this, new Observer<LoginResult>() {
            @Override
            public void onChanged(@Nullable LoginResult loginResult) {
                if (loginResult == null) {
                    return;
                }
                loadingProgressBar.setVisibility(View.GONE);
                if (loginResult.getError() != null) {
                    showLoginFailed(loginResult.getError());
                }
                if (loginResult.getSuccess() != null) {
                    updateUiWithUser(loginResult.getSuccess());
                }
                setResult(Activity.RESULT_OK);

                //Complete and destroy login activity once successful
                finish();
            }
        });

        TextWatcher afterTextChangedListener = new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                // ignore
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                // ignore
            }

            @Override
            public void afterTextChanged(Editable s) {
                loginViewModel.loginDataChanged(usernameEditText.getText().toString(),
                        passwordEditText.getText().toString());
            }
        };
        usernameEditText.addTextChangedListener(afterTextChangedListener);
        passwordEditText.addTextChangedListener(afterTextChangedListener);
        passwordEditText.setOnEditorActionListener(new TextView.OnEditorActionListener() {

            @Override
            public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
                if (actionId == EditorInfo.IME_ACTION_DONE) {
                    loginViewModel.login(usernameEditText.getText().toString(),
                            passwordEditText.getText().toString());
                }
                return false;
            }
        });

        loginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                loadingProgressBar.setVisibility(View.VISIBLE);
                loginViewModel.login(usernameEditText.getText().toString(),
                        passwordEditText.getText().toString());
            }
        });
    }

    private void updateUiWithUser(LoggedInUserView model) {
        String welcome = getString(R.string.welcome) + model.getDisplayName();
        // TODO : initiate successful logged in experience
        Toast.makeText(getApplicationContext(), welcome, Toast.LENGTH_LONG).show();
    }

    private void showLoginFailed(@StringRes Integer errorString) {
        Toast.makeText(getApplicationContext(), errorString, Toast.LENGTH_SHORT).show();
    }
}

Answer 1

我也在寻找一个好的解决方案。目前我最终实现了 2 个 Listeners 接口(interface)。

public interface OnLoginListener {
    void onLoginResult(Result result);
}
public interface OnRegistrationListener {
    void onRegistrationResult(Result result);
}

我让我的 ViewModel 实现了这些接口(interface)并相应地更改了 UI，我不确定这是否遵循了 MVVM 模式的最佳实践。LoginDataSource 被传递给监听器的引用

private OnLoginListener onLoginListener;
private OnRegistrationListener onRegistrationListener;

并从 onPostExecute 调用 onRegistrationResult 方法，或者像我的情况一样从 Firebase 身份验证的 onComplete 方法调用。

@Override
        public void onComplete(@NonNull Task<AuthResult> task) {
            if (task.isSuccessful()) {
                // Sign in success, update UI with the signed-in user's information
                Log.d(TAG, "createUserWithEmail:success");
                FirebaseUser user = mAuth.getCurrentUser();
                onRegistrationListener.onRegistrationResult(new Result.Success<>(user));
            } else {
                // If sign in fails, display a message to the user.
                Log.w(TAG, "createUserWithEmail:failure", task.getException());
                onRegistrationListener.onRegistrationResult(new Result.Error(task.getException()));
            }
        }

我希望这对某人有帮助；)。