异步任务结束后开始意图 [英] Starting intent after Async task gets over

问题描述

我为我的 Android 应用创建了一个登录活动.用户输入正确的凭据后，登录活动将切换到主页，但我不知道为什么我的代码不会切换并且我的logcat中没有显示错误.清单也已正确定义.

I created a login activity for my Android app. After the user enters the correct credentials, the login activity will switch over to the homepage but I don't know why my code won't switch and there is no error shown in my logcat. The manifest was also properly defined.

这是我的登录活动:

public class LoginEmployerActivity extends Activity { 
Button btnLoginEmployer; 
Button btnLinkToEmployerRegisterScreen; 
EditText inputEmail; 
EditText inputPassword; 
TextView loginErrorMsg; 
TextView forgotPassword; 

// JSON Response node names 
private static String KEY_SUCCESS = "success"; 
private static String KEY_ERROR = "error"; 
private static String KEY_ERROR_MSG = "error_msg"; 
private static String KEY_UID = "uid"; 
private static String KEY_NAME = "name"; 
private static String KEY_CNAME = "cname"; 
private static String KEY_EMAIL = "email"; 
private static String KEY_CREATED_AT = "created_at"; 
private ProgressDialog pDialog; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.login_employer); 

// Importing all assets like buttons, text fields 
inputEmail = (EditText) findViewById(R.id.loginEmployerEmail); 
inputPassword = (EditText) findViewById(R.id.loginEmployerPassword); 
btnLoginEmployer = (Button) findViewById(R.id.btnLoginEmployer); 
btnLinkToEmployerRegisterScreen = (Button) findViewById(R.id.btnLinkToEmployerRegisterScreen); 
loginErrorMsg = (TextView) findViewById(R.id.login_error); 
forgotPassword = (TextView) findViewById(R.id.link_to_forgetPassword); 

// Login button Click Event 
btnLoginEmployer.setOnClickListener(new View.OnClickListener() { 

    public void onClick(View view) { 
        // Checking for server respond 
            new LoginEmployer().execute(); 
        } 
    } 
}); 

// Link to Register Screen 
btnLinkToEmployerRegisterScreen 
        .setOnClickListener(new View.OnClickListener() { 

            public void onClick(View view) { 
                Intent i = new Intent(getApplicationContext(), 
                        RegisterEmployerActivity.class); 
                startActivity(i); 
                finish(); 
            } 
        }); 

// Link to forgot password link 
forgotPassword.setOnClickListener(new View.OnClickListener() { 
    public void onClick(View view) { 
        // Switching to forgot password screen 
        Intent i = new Intent(getApplicationContext(), 
                ForgotPasswordEmployerActivity.class); 
        startActivity(i); 
    } 
}); 
} 

// Background ASYNC Task to login by making HTTP Request 
class LoginEmployer extends AsyncTask<String, String, String> { 

// Before starting background thread Show Progress Dialog 
@Override 
protected void onPreExecute() { 
    super.onPreExecute(); 
    pDialog = new ProgressDialog(LoginEmployerActivity.this); 
    pDialog.setMessage("Authenticating..."); 
    pDialog.setIndeterminate(false); 
    pDialog.setCancelable(false); 
    pDialog.show(); 
} 

// Checking login in background 
protected String doInBackground(String... params) { 
    runOnUiThread(new Runnable() { 
        public void run() { 

            String email = inputEmail.getText().toString(); 
            String password = inputPassword.getText().toString(); 
            EmployerFunctions employerFunctions = new EmployerFunctions(); 
            JSONObject json = employerFunctions.loginUser(email, 
                    password); 

            // check for login response 
            try { 
                if (json.getString(KEY_SUCCESS) != null) { 
                    loginErrorMsg.setText(""); 
                    String res = json.getString(KEY_SUCCESS); 
                    if (Integer.parseInt(res) == 1) { 
                        // user successfully logged in 
                        // Store user details in SQLite Database 
                        DatabaseHandlerEmployer dbe = new DatabaseHandlerEmployer( 
                                getApplicationContext()); 
                        JSONObject json_user = json 
                                .getJSONObject("user"); 

                        // Clear all previous data in database 
                        employerFunctions 
                                .logoutUser(getApplicationContext()); 
                        dbe.addUser( 
                                json_user.getString(KEY_NAME), 
                                //json_user.getString(KEY_CNAME), 
                                json_user.getString(KEY_EMAIL), 
                                json.getString(KEY_UID), 
                                json_user.getString(KEY_CREATED_AT)); 
                        // Launch Employer homePage Screen 
                        Intent homepage = new Intent( 
                                getApplicationContext(), 
                                HomepageEmployerActivity.class); 

                        // Close all views before launching Employer 
                        // homePage 
                        homepage.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
                        startActivity(homepage); 

                        // Close Login Screen 
                        finish(); 
                    } else { 
                        // Error in login 
                        loginErrorMsg 
                                .setText("Invalid username/password"); 
                    } 
                } 
            } catch (JSONException e) { 
                e.printStackTrace(); 
            } 
        } 
    }); 
    return null; 
} 

// After completing background task Dismiss the progress dialog 
protected void onPostExecute(String file_url) { 
    // dismiss the dialog once done 
    pDialog.dismiss(); 
} 
} 
}

将意图语句移动到 onPostExecute 方法后的编辑代码

EDITED CODE AFTER MOVING INTENT STATEMENT TO onPostExecute METHOD

public class LoginEmployerActivity extends Activity {
Button btnLoginEmployer;
Button btnLinkToEmployerRegisterScreen;
EditText inputEmail;
EditText inputPassword;
TextView loginErrorMsg;
TextView forgotPassword;

// JSON Response node names
private static String KEY_SUCCESS = "success";
private static String KEY_ERROR = "error";
private static String KEY_ERROR_MSG = "error_msg";
private static String KEY_UID = "uid";
private static String KEY_NAME = "name";
private static String KEY_CNAME = "cname";
private static String KEY_EMAIL = "email";
private static String KEY_CREATED_AT = "created_at";
private ProgressDialog pDialog;

boolean loginVerify= false;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.login_employer);

    // Importing all assets like buttons, text fields
    inputEmail = (EditText) findViewById(R.id.loginEmployerEmail);
    inputPassword = (EditText) findViewById(R.id.loginEmployerPassword);
    btnLoginEmployer = (Button) findViewById(R.id.btnLoginEmployer);
    btnLinkToEmployerRegisterScreen = (Button) findViewById(R.id.btnLinkToEmployerRegisterScreen);
    loginErrorMsg = (TextView) findViewById(R.id.login_error);
    forgotPassword = (TextView) findViewById(R.id.link_to_forgetPassword);

    // Login button Click Event
    btnLoginEmployer.setOnClickListener(new View.OnClickListener() {

        public void onClick(View view) {
            // Checking for server respond
                new LoginEmployer().execute();
            }
        }
    });

    // Link to Register Screen
    btnLinkToEmployerRegisterScreen
            .setOnClickListener(new View.OnClickListener() {

                public void onClick(View view) {
                    Intent i = new Intent(getApplicationContext(),
                            RegisterEmployerActivity.class);
                    startActivity(i);
                    finish();
                }
            });

    // Link to forgot password link
    forgotPassword.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            // Switching to forgot password screen
            Intent i = new Intent(getApplicationContext(),
                    ForgotPasswordEmployerActivity.class);
            startActivity(i);
        }
    });
}

// Background ASYNC Task to login by making HTTP Request
class LoginEmployer extends AsyncTask<String, String, String> {

    // Before starting background thread Show Progress Dialog
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(LoginEmployerActivity.this);
        pDialog.setMessage("Authenticating...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();
    }

    // Checking login in background
    protected String doInBackground(String... params) {
        runOnUiThread(new Runnable() {
            public void run() {

                String email = inputEmail.getText().toString();
                String password = inputPassword.getText().toString();
                EmployerFunctions employerFunctions = new EmployerFunctions();
                JSONObject json = employerFunctions.loginUser(email,
                        password);

                // check for login response
                try {
                    if (json.getString(KEY_SUCCESS) != null) {
                        loginErrorMsg.setText("");
                        String res = json.getString(KEY_SUCCESS);
                        if (Integer.parseInt(res) == 1) {
                            loginVerify = true;
                            // user successfully logged in
                            // Store user details in SQLite Database
                            DatabaseHandlerEmployer dbe = new DatabaseHandlerEmployer(
                                    getApplicationContext());
                            JSONObject json_user = json
                                    .getJSONObject("user");

                            // Clear all previous data in database
                            employerFunctions
                                    .logoutUser(getApplicationContext());
                            dbe.addUser(
                                    json_user.getString(KEY_NAME),
                                    json_user.getString(KEY_CNAME),
                                    json_user.getString(KEY_EMAIL),
                                    json.getString(KEY_UID),
                                    json_user.getString(KEY_CREATED_AT));

                        } else {
                            // Error in login
                            loginErrorMsg
                                    .setText("Invalid username/password");
                        }
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        });
        return null;
    }

    // After completing background task Dismiss the progress dialog
    protected void onPostExecute(String file_url) {
        // dismiss the dialog once done
        pDialog.dismiss();
        if ( loginVerify == true ) 
        {
        // Launch Employer homePage Screen
        Intent homepage = new Intent(getApplicationContext(),
                HomepageEmployerActivity.class);

        // Close all views before launching Employer
        // homePage
        homepage.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(homepage);

        // Close Login Screen
        finish();
        }
    }
}

}

推荐答案

您正在调用在 doInBackgorund() 中启动新活动的意图，该活动在非 UI 线程上运行，并且该活动需要在 UI 上运行线.这就是您的登录活动永不停止的原因.

You are calling the intent to start a new activity inside the doInBackgorund() which runs on a non-UI thread and the Activity needs to be run on a UI thread. That is why your Login activity is never stopped.

将代码放入 onPostExecute() 或 onProgressUpdate() 内的新活动.

Put the code to go to the new activity inside onPostExecute() or onProgressUpdate().

这是您可以做的事情.声明一个全局变量 loginVerfied = false;

Here is something you can do. Declare a global variable loginVerfied = false;

当你的 doInBackground 验证用户的真实性时，使 loginVerified = true ，否则保持它 false.

When your doInBackground verifies that the authenticity of the user, make loginVerified = true , otherwise keep it false.

然后在onPostExecute()

if(loginVerifed == true)
{
       Intent homepage = new Intent(getApplicationContext(),HomepageEmployerActivity.class                               
       homepage.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
       startActivity(homepage);
       finish();
}

另外，你已经声明了class LoginEmployer extends AsyncTask，所以要调用它你需要使用new LoginEmployer.execute("");(您缺少双引号并且没有将任何字符串传递给任务，因此它与它的参数不匹配).AsyncTask 定义中的第一个参数是调用 execute() 函数时传递给它的值的数据类型.第二个参数是与后台线程运行期间显示进度相关的数据类型.第三个参数指定结果的返回值.

Also, you have declared class LoginEmployer extends AsyncTask<String, String, String>, so to call it you need to use new LoginEmployer.execute(""); (you are missing the double quotes and not passing any String to the Task so it does not match it's parameters). The first parameter in the definition of the AsyncTask is the datatype of the value being passed to it when execute() function is called. The second parameter is the datatype related to displaying progress during the time when the background thread runs. And the third parameter specifies the return value of the result.

有关 AsyncTask 的更多信息此处.

More about AsyncTask here.

所以，这是您现在需要做的.

So, here is what you need to do now.

像这样声明异步任务.

class LoginEmployer 扩展 AsyncTask 并使用 new LoginEmployer.execute("") 调用它.确保从您的 doInBackground() 中return null.

class LoginEmployer extends AsyncTask<String, Void, String> and make a call to it by using new LoginEmployer.execute(""). Make sure to return null from your doInBackground().

希望现在可以解决您的问题！

Hope this solves your problem now!

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