java - 在 Android Studio 中将数据从 MySQL 显示到 TextView

Question

我想使用 TextView 将 MySQL 中的数据显示到 Android 中，但是当我运行该应用程序时，它会强制自行停止。

谁能帮我解决一下？任何想法都会很好。

dbconfig.php:

<?php

//This script is designed by Android-Examples.com
//Define your host here.
$servername = "localhost";
//Define your database username here.
$username = "root";
//Define your database password here.
$password = "";
//Define your database name here.
$dbname = "u727224026_demo";

?>

send_data.php

<?php
include 'dbconfig.php';


// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

$sql = "SELECT * FROM TextViewTable";
$result = $conn->query($sql);

if ($result->num_rows > 0) {

    // output data of each row
    while($row[] = $result->fetch_assoc()) {

       $json = json_encode($row);


    }
} else {
    echo "0 results";
}
echo $json;
$conn->close();
?>

MainActivity.java

package flix.yudi.kuesioner2;

import java.io.IOException;

import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

public class MainActivity extends Activity {

    TextView textview;
    JSONObject json = null;
    String str = "";
    HttpResponse response;
    Context context;
    ProgressBar progressbar;
    Button button;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        progressbar = (ProgressBar)findViewById(R.id.progressBar1);
        textview = (TextView)findViewById(R.id.textView1);
        button = (Button)findViewById(R.id.button1);

        progressbar.setVisibility(View.GONE);

        button.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                progressbar.setVisibility(View.VISIBLE);

                new GetTextViewData(context).execute();

            }
        });
    }


    private class GetTextViewData extends AsyncTask<Void, Void, Void>
    {
        public Context context;


        public GetTextViewData(Context context)
        {
            this.context = context;
        }

        @Override
        protected void onPreExecute()
        {
            super.onPreExecute();
        }

        @Override
        protected Void doInBackground(Void... arg0)
        {

            HttpClient myClient = new DefaultHttpClient();
            HttpPost myConnection = new HttpPost("http://192.168.100.6/a_test/send-data.php");

            try {
                response = myClient.execute(myConnection);
                str = EntityUtils.toString(response.getEntity(), "UTF-8");

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


            try{
                JSONArray jArray = new JSONArray(str);
                json = jArray.getJSONObject(0);



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

            catch (Exception e)
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return null;
        }
        protected void onPostExecute(Void result)
        {
            try {
                textview.setText(json.getString("ServerData"));

            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            //Hiding progress bar after done loading TextView.
            progressbar.setVisibility(View.GONE);

        }
    }


}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.jsonparsingfromurltextview_android_examples.com.MainActivity" >

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:text="TextView Static Text Before Load"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:gravity="center"/>

<ProgressBar
    android:id="@+id/progressBar1"
    style="?android:attr/progressBarStyleLarge"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView1"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="17dp" />

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="150dp"
    android:text="Click Here to Load TextView data dynamically from MySQL Database Online Using JSON Parsing" />

logcat 错误通知

10-04 15:41:44.516 22210-22210/flix.yudi.kuesioner2 E/AndroidRuntime: FATAL EXCEPTION: main Process: flix.yudi.kuesioner2, PID: 22210 java.lang.NullPointerException at flix.yudi.kuesioner2.MainActivity$GetTextViewData.onPostExecute(MainActivity.java:114) at flix.yudi.kuesioner2.MainActivity$GetTextViewData.onPostExecute(MainActivity.java:60) at android.os.AsyncTask.finish(AsyncTask.java:632) at android.os.AsyncTask.access$600(AsyncTask.java:177) at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:146) at android.app.ActivityThread.main(ActivityThread.java:5593) 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:1283) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099) at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132) at dalvik.system.NativeStart.main(Native Method)

我试图找到修复它的方法，但还是一无所获， 请帮助我。

来自 HTTP_REQUESTER 的附加信息响应:

Answer 1

问题好像出在新这一行

new GetTextViewData(context).execute();

Context 是一个指针，但没有引用任何内容...这会导致空指针异常。

在传递上下文时使用:

new GetTextViewData(this).execute();

希望这对您有所帮助。