我一直在使用php和MySQL开发网页多年，但我不熟悉Android项目的开发。我搜索并阅读了我之前发现的有关该主题的所有问题，但没有找到适用于我的项目的答案。目前，当我运行应用程序时，我得到的只是错误而且没有下载。我发布了我的主要活动的完整代码，并询问是否有人可以解释我做错了什么。 UserId的共享偏好中的数据是整数，日期/会话是数字字符串，电子邮件/地址是字符串
package com.example.logintest;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
public class MainActivity extends AppCompatActivity {
String IgidPreference = "IgidPreference";
String UserId = "userId";
String Date = "session";
//OR SHOULD THE DECLEARATION BE??
//public static final String UserId = "userId";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
new VerifyLogin().execute();
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(MainActivity.this, Login.class);
startActivity(intent);
}
});
}
public class VerifyLogin extends AsyncTask<String, Void, String> {
Context ctx;
SharedPreferences pref;
protected void onPreExecute() {
}
@Override
protected String doInBackground(String... arg0) {
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(ctx);
if ((pref.contains(UserId)) && (pref.contains(Date))) {
}
String eaddress = arg0[0];
String today = arg0[1];
String link;
String data;
BufferedReader bufferedReader;
String result;
try {
data = "?Email=" + URLEncoder.encode(eaddress, "UTF-8");
data += "&Date=" + URLEncoder.encode(today, "UTF-8");
link = "http://domain.com/verifylogin.php" + data;
URL url = new URL(link);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
result = bufferedReader.readLine();
return result;
} catch (Exception e) {
return new String("Exception: " + e.getMessage());
}
}
@Override
protected void onPostExecute(String result) {
String jsonStr = result;
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
String userId = jsonObj.getString("user_id");
String session = jsonObj.getString("session");
String error_type = jsonObj.getString("error");
String error_msg = jsonObj.getString("error_msg");
if (error_type.equals("FALSE")) {
pref = context.getSharedPreferences(IgidPreference, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = pref.edit();
editor.putString(UserId, userId);
editor.putString(Date, session);
editor.apply();
Intent intent = new Intent(MainActivity.this, Account.class);
startActivity(intent);
} else if (error_type.equals("TRUE")) {
Toast.makeText(context, error_msg, Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(context, error_msg, Toast.LENGTH_SHORT).show();
}
} catch (JSONException e) {
e.printStackTrace();
Toast.makeText(context, "Error parsing JSON data.", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(context, "Couldn't get any JSON data.", Toast.LENGTH_SHORT).show();
}
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
答案 0 :(得分：1)
我知道自从发布主题以来已经有一段时间但是我不得不更换电脑，以及Android Studio并制作所有新项目。
以下是我发现处理原始问题的方法。我在代码中添加了注释，以帮助其他想要为下一个项目使用代码的人。
public class LoginActivity extends Activity { //Standard Activity code
Button BtnLaunchSigninActivity; //Button to click
private EditText etLoginUserName, etLoginPassword; // data to submit
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
etLoginUserName = (EditText) findViewById(R.id.etLoginUserName);
etLoginPassword = (EditText) findViewById(R.id.etLoginPassword);
BtnLaunchSigninActivity = (Button) findViewById(R.id.btnLoginSignin);
BtnLaunchSigninActivity.setOnClickListener(onClickListener);
}
private View.OnClickListener onClickListener = new View.OnClickListener() {
@Override
public void onClick(View v) {
if (v.getId() == R.id.btnLoginSignin) {
signin(v);
}
}
};
public void signin(View v) {
String userName = etLoginUserName.getText().toString();
String passWord = etLoginPassword.getText().toString();
Toast.makeText(this, "Signing In...", Toast.LENGTH_SHORT).show();
new SignIn(this).execute(userName, passWord); // Send data to AsyncTask
}
private class SignIn extends AsyncTask<String, Void, String> {
private Context context; // context is for the SignIn()
SignIn(Context context) {
this.context = context;
}
protected void onPreExecute() {
}
@Override
protected String doInBackground(String... arg0) {
String userName = arg0[0];
String passWord = arg0[1];
String link;
String data;
BufferedReader bufferedReader;
String result;
try {
data = "?username=" + URLEncoder.encode(userName, "UTF-8");
data += "&password=" + URLEncoder.encode(passWord, "UTF-8");
link = "url/login.php" + data;
URL url = new URL(link);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
result = bufferedReader.readLine();
return result; // My php returns jsonobjects
} catch (Exception e) {
return new String("Exception: " + e.getMessage());
}
}
@Override
protected void onPostExecute(String result) {
String jsonStr = result; //turn object into string
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
String status = jsonObj.getString("status");
String userid = jsonObj.getString("uid");
String hash = jsonObj.getString("security");
Log.d("tag", jsonObj.toString(4));
if (status.equals("Good")) {
Toast.makeText(context, "Sign In successful.", Toast.LENGTH_SHORT).show();
//YOU HAVE TO USE JSONSTR TO GET USERID AND SECHASH FOR UPDATING SHARED PREFERENCES
//DUE TO ANY POSSIBLE DELAYS OF PROCESSING doInBackground() SEND JSON TO NEXT ACTIVITY TO SET PREFERENCES
//ADD THE STRING TO THE INTENT BELOW, THEN PROCESS THE DATA FOR SETTING SHAREDPREFERENCES IN THE NEXT ACTIVITY
Log.d("UserID",userid);
Log.d("SecHash", hash);
Intent intent = new Intent(LoginActivity.this, HomeActivity.class);
Bundle extras = new Bundle();
extras.putString("USERID",jsonObj.getString("uid"));
extras.putString("SECHASH",jsonObj.getString("security"));
extras.putString("USERID","userid");
extras.putString("SECHASH","hash");
intent.putExtras(extras);
startActivity(intent);
} else if (status.equals("Wrong")) {
Toast.makeText(context, "Username/Password is incorrect, could not be verified. Sign In failed.", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(context, "Couldn't connect to remote database.", Toast.LENGTH_SHORT).show();
}
} catch (JSONException e) {
e.printStackTrace();
Toast.makeText(context, "Error parsing JSON data.", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(context, "Couldn't get any JSON data.", Toast.LENGTH_SHORT).show();
}
}
}
}
在下一个活动中，从意图中获取额外内容并将其添加到sharedPreferences中。这就是它的全部内容。
感谢大家以前的帮助。我希望这将有助于将来发现同样问题的其他人。
答案 1 :(得分：0)
在doInBackground()中，您定义了一个区域设置变量，但使用了成员变量
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(ctx);
if ((pref.contains(UserId)) && (pref.contains(Date))) {
}
由于您只在pref分配onPostExecute()，因此您每次都会获得NullPointerExceptions。此外，ctx为空，甚至未声明context。因此，请确保尽早定义pref。
public class VerifyLogin extends AsyncTask<String, Void, String> {
private final SharedPreferences pref;
VerifyLogin() {
pref = getSharedPreferences(IgidPreference, Context.MODE_PRIVATE);
}
[...]
}
但最终你不应该像这样实现它。你会在这里泄露你的活动！