单击按钮时应用程序停止

Question

我想通过接收来自此服务器的数据来检查与服务器的连接，这是我的代码：

  package com.example.sanzharaubakir.fin;

import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.io.IOException;
import java.net.MalformedURLException;
import java.util.ArrayList;
import java.util.List;

import cz.msebera.android.httpclient.HttpEntity;
import cz.msebera.android.httpclient.HttpResponse;
import cz.msebera.android.httpclient.NameValuePair;
import cz.msebera.android.httpclient.client.ClientProtocolException;
import cz.msebera.android.httpclient.client.HttpClient;
import cz.msebera.android.httpclient.client.entity.UrlEncodedFormEntity;
import cz.msebera.android.httpclient.client.methods.HttpPost;
import cz.msebera.android.httpclient.impl.client.DefaultHttpClient;
import cz.msebera.android.httpclient.message.BasicNameValuePair;
import cz.msebera.android.httpclient.util.EntityUtils;

/**
 * Created by sanzharaubakir on 26.07.16.
 */
public class auth extends Activity {
    EditText login;
    EditText pswd;
    Button ok;
    MyTask task;
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.authorization);
        ok = (Button) findViewById(R.id.ok);
        ok.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                //task = new MyTask();
                //task.execute();
                new MyTask().doInBackground();
            }
        });
    }



    public class MyTask extends AsyncTask<Void, Void, Void> {

        @Override
        protected Void doInBackground(Void... voids) {
            sendData();
            return null;
        }

       /* @Override
        protected void onPreExecute() {
        }

        protected void onPostExecute(Void result) {
        }*/
    }
    public void sendData()
    {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost("http://144.76.29.144:8001/documents/api/login");
        try {
            String log = login.getText().toString();
            String psw = pswd.getText().toString();
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
            nameValuePairs.add(new BasicNameValuePair("username", log));
            nameValuePairs.add(new BasicNameValuePair("password", psw));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            HttpResponse response = httpclient.execute(httppost);

            int responseCode = response.getStatusLine().getStatusCode();
            String tk = EntityUtils.toString(response.getEntity());
            if (responseCode == 200)
            {
                SharedPreferences sPref = getPreferences(MODE_PRIVATE);
                SharedPreferences.Editor e = sPref.edit();
                e.putString("token", tk);
                e.apply();
                Intent intent = getIntent();
                String info = intent.getStringExtra("d");
                try {
                    HttpClient client = new DefaultHttpClient();
                    HttpPost Post = new HttpPost("http://144.76.29.144:8001");
                    List<NameValuePair> ValuePairs = new ArrayList<NameValuePair>(2);
                    ValuePairs.add(new BasicNameValuePair("data", info));
                    ValuePairs.add(new BasicNameValuePair("token", tk));

                    Post.setEntity(new UrlEncodedFormEntity(ValuePairs,"UTF-8"));
                    HttpResponse httpResponse = client.execute(Post);
                    HttpEntity httpEntity = httpResponse.getEntity();
                    info = EntityUtils.toString(httpEntity,"UTF-8");


                } catch (MalformedURLException ex) {
                    ex.printStackTrace();

                } catch (IOException ex) {

                    ex.printStackTrace();
                }
            }
            else {

            }
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
        } catch (IOException e) {
            // TODO Auto-generated catch block
        }
    }
}

和XML

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Login"
        />
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/login"
        />
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Password"
            />
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/pswd"
            />
    </LinearLayout>
    <Button
        android:id="@+id/ok"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
        android:text="Log in"
        />
</LinearLayout>

当我尝试点击按钮时，应用程序不幸停止，是否有人知道它为什么会发生？ 以下是Log所说的：

FATAL EXCEPTION: main
                                                                              Process: com.example.sanzharaubakir.fin, PID: 2620
                                                                              java.lang.NullPointerException
                                                                                  at com.example.sanzharaubakir.fin.auth.sendData(auth.java:76)
                                                                                  at com.example.sanzharaubakir.fin.auth$MyTask.doInBackground(auth.java:60)
                                                                                  at com.example.sanzharaubakir.fin.auth$1.onClick(auth.java:47)
                                                                                  at android.view.View.performClick(View.java:4438)
                                                                                  at android.view.View$PerformClick.run(View.java:18422)
                                                                                  at android.os.Handler.handleCallback(Handler.java:733)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                  at android.os.Looper.loop(Looper.java:136)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:5017)
                                                                                  at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                  at java.lang.reflect.Method.invoke(Method.java:515)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
                                                                                  at dalvik.system.NativeStart.main(Native Method)

Answer 1

您正在主线程上进行网络操作。尝试在单独的线程中进行。使用Asynctask。

Answer 2

使用异步任务进行呼叫网络服务。

Answer 3

请记住：建议所有耗时的操作（如网络操作和读取数据库）在后台线程中运行，而不是在UI线程中运行。因为它们可能会导致ANR异常。您可以使用AsyncTask或仅使用新的子线程来生成http请求并在主线程（UI线程）中显示该接口。顺便说一句，如果你在Android 2.2之上运行，我建议使用HttpUrlConnection而不是HttpClient。

编辑：使用AsyncTask。

您无法直接调用doInBackground方法，您可以尝试以下代码供您参考。

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.your_layout);
    ...
    ok.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            new MyTask().execute();     //you can't invoke the doInBackground method directly
        }
    });
}

public class MyTask extends AsyncTask<Void, Void, Void> {

    /**
     * Runs on the UI thread before doInBackground, does preloading works generally speaking
     */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    /**
     * Runs on the background thread, does time-consuming operations
     */
    @Override
    protected Void doInBackground(Void... params) {
        // when you finish loading, you can call publishProgress to publish updates on the UI thread
        return null;
    }

    /**
     * Runs on the UI thread after publishProgress is invoked.
     */
    @Override
    protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
        // you can update the loading progress here
    }

    /**
     * Runs on the UI thread after doInBackground
     * This method won't be invoked if the task was cancelled
     */
    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
    }
}