Question

我的应用从数据库接收数据以进行授权和注册。当startActivity(new Intent(this, Main.class));时 line被评论出应用程序只是最小化，当取消注释它崩溃。

的Manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.littledev.test_v2">
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".Login">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".Main">

        </activity>
    </application>

</manifest>

Login.java

package com.example.littledev.test_v2;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;

public class Login extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
    }

    public void onLoginSuccess() {
        startActivity(new Intent(this, Main.class));
    }

    public void onLogin(View view){
        EditText eLogin = (EditText) findViewById(R.id.username);
        EditText ePass = (EditText) findViewById(R.id.password);
        String login = eLogin.getText().toString();
        String pass = ePass.getText().toString();
        Sql_bridge bridge = new Sql_bridge(this);
        bridge.execute("login",login,pass);
        finish();
    }

    public void onRegister(View view) {
        //startActivity(new Intent(this, Register.class));
    }
}

Sql_bridge.java

package com.example.littledev.test_v2;

import android.app.AlertDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;

/**
 * Created by LittleDev on 3/30/2017.
 */

public class Sql_bridge extends AsyncTask<String,Void,String> {
    private Context ctx;
    Sql_bridge (Context ctx)
    {
        this.ctx =ctx;
    }
    @Override
    protected void onPreExecute() {
        AlertDialog alertDialog;
        alertDialog = new AlertDialog.Builder(ctx).create();
        alertDialog.setTitle("Main Information....");
    }

    @Override
    protected String doInBackground(String... params) {
        String reg_url = "http://e-shops.hol.es/app_register";
        String log_url = "http://e-shops.hol.es/app_login";
        String method = params[0];
        if (method.equals("register")) {
            String name = params[1];
            String surname = params[2];
            String email = params[3];
            String password = params[4];
            try {
                URL url = new URL(reg_url);
                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setDoOutput(true);
                httpURLConnection.setDoInput(true);
                OutputStream OS = httpURLConnection.getOutputStream();
                BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(OS, "UTF-8"));
                String data = URLEncoder.encode("name", "UTF-8") + "=" + URLEncoder.encode(name, "UTF-8") + "&" +
                        URLEncoder.encode("surname", "UTF-8") + "=" + URLEncoder.encode(surname, "UTF-8") + "&" +
                        URLEncoder.encode("password", "UTF-8") + "=" + URLEncoder.encode(password, "UTF-8") + "&" +
                        URLEncoder.encode("email", "UTF-8") + "=" + URLEncoder.encode(email, "UTF-8");
                bufferedWriter.write(data);
                bufferedWriter.flush();
                bufferedWriter.close();
                OS.close();
                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));
                String response = "";
                String line;
                while ((line = bufferedReader.readLine())!=null)
                {
                    response+= line;
                }
                bufferedReader.close();
                inputStream.close();
                httpURLConnection.disconnect();
                return response;
            } catch (IOException e) {
                e.printStackTrace();
            }
        }else if (method.equals("login")){
            String login_name = params[1];
            String login_pass = params[2];
            try {
                URL url = new URL(log_url);
                HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
                httpURLConnection.setRequestMethod("POST");
                httpURLConnection.setDoOutput(true);
                httpURLConnection.setDoInput(true);
                OutputStream outputStream = httpURLConnection.getOutputStream();
                BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream,"UTF-8"));
                String data = URLEncoder.encode("login","UTF-8")+"="+URLEncoder.encode(login_name,"UTF-8")+"&"+
                        URLEncoder.encode("password","UTF-8")+"="+URLEncoder.encode(login_pass,"UTF-8");
                bufferedWriter.write(data);
                bufferedWriter.flush();
                bufferedWriter.close();
                outputStream.close();

                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));
                String response = "";
                String line;
                while ((line = bufferedReader.readLine())!=null)
                {
                    response+= line;
                }
                bufferedReader.close();
                inputStream.close();
                httpURLConnection.disconnect();
                return response;


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

        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
    }

    @Override
    protected void onPostExecute(String result) {
        Login login = new Login();
        switch (result) {
            case "Registered":
                Toast.makeText(ctx, result, Toast.LENGTH_LONG).show();
                break;
            case "Login":
                Toast.makeText(ctx, result, Toast.LENGTH_LONG).show();
                login.onLoginSuccess();

                break;
            default:
                Toast.makeText(ctx, "Failed", Toast.LENGTH_LONG).show();
                break;
        }

    }
}

logcat的

03-30 15:11:48.323 9997-9997/com.example.littledev.test_v2 E/AndroidRuntime: FATAL EXCEPTION: main
                                                                             Process: com.example.littledev.test_v2, PID: 9997
                                                                             java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference
                                                                                 at android.app.Activity.startActivityForResult(Activity.java:4298)
                                                                                 at android.support.v4.app.BaseFragmentActivityJB.startActivityForResult(BaseFragmentActivityJB.java:50)
                                                                                 at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:79)
                                                                                 at android.app.Activity.startActivityForResult(Activity.java:4245)
                                                                                 at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:859)
                                                                                 at android.app.Activity.startActivity(Activity.java:4582)
                                                                                 at android.app.Activity.startActivity(Activity.java:4550)
                                                                                 at com.example.littledev.test_v2.Login.onLoginSuccess(Login.java:19)
                                                                                 at com.example.littledev.test_v2.Sql_bridge.onPostExecute(Sql_bridge.java:131)
                                                                                 at com.example.littledev.test_v2.Sql_bridge.onPostExecute(Sql_bridge.java:23)
                                                                                 at android.os.AsyncTask.finish(AsyncTask.java:651)
                                                                                 at android.os.AsyncTask.access$500(AsyncTask.java:180)
                                                                                 at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                 at android.os.Looper.loop(Looper.java:148)
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:7329)
                                                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
                                                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

我真的不知道为什么会崩溃。

Answer 1

public void onLoginSuccess() {
    startActivity(new Intent(Login.this, Main.class));
}

从onLogin方法中删除finish（）

因为AsyncTask工作背景你调用finish方法来完成当前活动。

public void onLogin(View view){
    EditText eLogin = (EditText) findViewById(R.id.username);
    EditText ePass = (EditText) findViewById(R.id.password);
    String login = eLogin.getText().toString();
    String pass = ePass.getText().toString();
    Sql_bridge bridge = new Sql_bridge(this);
    bridge.execute("login",login,pass);
   // finish(); remove it
}

Answer 2

您是否尝试从finish()删除onLogin()并仅在收到登录结果时调用它？

public void onLoginSuccess() {
    finish();
    startActivity(new Intent(this, Main.class));
}

Answer 3

在第一个参数中使用当前活动上下文

startActivity(new Intent(Login.this, Main.class));

Answer 4

你不能新建一个活动。

package com.example.littledev.test_v2;
import android.app.AlertDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
public class Sql_bridge extends AsyncTask<String,Void,String> {
private Activity ctx;
Sql_bridge (Activity ctx)
{
    this.ctx =ctx;
}

@Override
protected void onPostExecute(String result) {

    switch (result) {
        case "Registered":
            Toast.makeText(ctx, result, Toast.LENGTH_LONG).show();
            break;
        case "Login":
            Toast.makeText(ctx, result, Toast.LENGTH_LONG).show();
            if(ctx instanceof Login){
                ((Login)ctx).onLoginSuccess();
            }
            break;
        default:
            Toast.makeText(ctx, "Failed", Toast.LENGTH_LONG).show();
            break;
    }

}
}

并删除finish（）：

public void onLogin(View view){
    EditText eLogin = (EditText) findViewById(R.id.username);
    EditText ePass = (EditText) findViewById(R.id.password);
    String login = eLogin.getText().toString();
    String pass = ePass.getText().toString();
    Sql_bridge bridge = new Sql_bridge(this);
    bridge.execute("login",login,pass);
}

并在登录成功时调用完成：

public void onLoginSuccess() {
    startActivity(new Intent(this, Main.class));
    finish();
}

Answer 5

@sasilKumar和@Jaydeep Patel说：在onLogin()中的Login.java方法中，您在启动Sql_bridge异步任务实例之后立即调用了finish（），并且在result中onPostExecute(String result)之后调用onLoginSuccess（）之前就已经过了MainThread 1 {}在<%@ Page Language="C#" Inherits="sbmanager.mgrGridHome" MasterPageFile="~/masterpages/global.master" %>上，那是什么引发了异常。

启动活动崩溃app应用程序是minimazin

的Manifest.xml

Login.java

Sql_bridge.java

logcat的

5 个答案: