如何在asynctask中调用意图，或者如何在onPostExecute中启动新活动？

Question

如何在asynctask中调用意图？ 或如何在onPostExecute中启动新活动？

我想在检查用户名和密码正确之后开始新的活动。

请帮助我，我尝试这样做。但是它总是进入新活动并且不检查用户名和密码。

MainActivity.java

 package com.example.puen.mysqldemo; import android.content.Intent; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.view.View; import android.widget.EditText; public class MainActivity extends AppCompatActivity { EditText UsernameEt ,PasswordEt; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); UsernameEt = (EditText)findViewById(R.id.etUserName); PasswordEt = (EditText)findViewById(R.id.etPassword); } public void OnLogin(View view) { String username = UsernameEt.getText().toString(); String password = PasswordEt.getText().toString(); String type = "login"; BackgroundWorker backgroundWorker = new BackgroundWorker(this); backgroundWorker.execute(type, username, password); } public void OpenReg(View view){ startActivity(new Intent(this,Register.class)); } public void getJSONClick(View view){ startActivity(new Intent(this, getDatabase.class)); } } 

Backgroundwrok.java

 package com.example.puen.mysqldemo; import android.app.AlertDialog; import android.content.Context; import android.os.AsyncTask; 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.MalformedURLException; import java.net.URL; import java.net.URLEncoder; /** * Created by puen on 4/6/2016. */ public class BackgroundWorker extends AsyncTask<String,Void,String> { Context context; AlertDialog alertDialog; BackgroundWorker (Context ctx){ context = ctx; } @Override protected String doInBackground(String... params) { String type = params[0]; String login_url = "http://192.168.10.125/login.php"; String register_url = "http://192.168.10.125/register.php"; if(type.equals("login")){ try { String user_name = params[1]; String password = params[2]; URL url = new URL(login_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 post_data = URLEncoder.encode("user_name","UTF-8")+"="+URLEncoder.encode(user_name,"UTF-8")+"&" +URLEncoder.encode("password","UTF-8")+"="+URLEncoder.encode(password,"UTF-8"); bufferedWriter.write(post_data); bufferedWriter.flush(); bufferedWriter.close(); outputStream.close(); InputStream inputStream = httpURLConnection.getInputStream(); BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1")); String result=""; String line=""; while ((line = bufferedReader.readLine())!= null){ result += line; } bufferedReader.close(); inputStream.close(); httpURLConnection.disconnect(); return result; } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }else if (type.equals("register")){ try { String name = params[1]; String surname = params[2]; String age = params[3]; String username = params[4]; String password = params[5]; URL url = new URL(register_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 post_data = URLEncoder.encode("name","UTF-8")+"="+URLEncoder.encode(name,"UTF-8")+"&" +URLEncoder.encode("surname","UTF-8")+"="+URLEncoder.encode(surname,"UTF-8")+"&" +URLEncoder.encode("age","UTF-8")+"="+URLEncoder.encode(age,"UTF-8")+"&" +URLEncoder.encode("username","UTF-8")+"="+URLEncoder.encode(username,"UTF-8")+"&" +URLEncoder.encode("password","UTF-8")+"="+URLEncoder.encode(password,"UTF-8"); bufferedWriter.write(post_data); bufferedWriter.flush(); bufferedWriter.close(); outputStream.close(); InputStream inputStream = httpURLConnection.getInputStream(); BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1")); String result=""; String line=""; while ((line = bufferedReader.readLine())!= null){ result += line; } bufferedReader.close(); inputStream.close(); httpURLConnection.disconnect(); return result; } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } return null; } @Override protected void onPreExecute() { alertDialog = new AlertDialog.Builder(context).create(); alertDialog.setTitle("Login Status"); } @Override protected void onPostExecute(String result) { alertDialog.setMessage(result); alertDialog.show(); } @Override protected void onProgressUpdate(Void... values) { super.onProgressUpdate(values); } }