[英]How to connect an Android application to a MySQL database?
我對Android應用程序編程非常陌生,所以請幫助我。 我想將我的應用程序連接到MySQL數據庫。
但是我收到一個使應用程序崩潰的錯誤。 這是LogCat中的錯誤:
07-26 12:32:47.785: E/AndroidRuntime(276): FATAL EXCEPTION: main
07-26 12:32:47.785: E/AndroidRuntime(276): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.massar_parent/com.example.parent.MainActivity}: java.lang.NullPointerException
07-26 12:32:47.785: E/AndroidRuntime(276): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
07-26 12:32:47.785: E/AndroidRuntime(276): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
07-26 12:32:47.785: E/AndroidRuntime(276): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
07-26 12:32:47.785: E/AndroidRuntime(276): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
07-26 12:32:47.785: E/AndroidRuntime(276): at android.os.Handler.dispatchMessage(Handler.java:99)
07-26 12:32:47.785: E/AndroidRuntime(276): at android.os.Looper.loop(Looper.java:123)
07-26 12:32:47.785: E/AndroidRuntime(276): at android.app.ActivityThread.main(ActivityThread.java:4627)
07-26 12:32:47.785: E/AndroidRuntime(276): at java.lang.reflect.Method.invokeNative(Native Method)
07-26 12:32:47.785: E/AndroidRuntime(276): at java.lang.reflect.Method.invoke(Method.java:521)
07-26 12:32:47.785: E/AndroidRuntime(276): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
07-26 12:32:47.785: E/AndroidRuntime(276): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
07-26 12:32:47.785: E/AndroidRuntime(276): at dalvik.system.NativeStart.main(Native Method)
07-26 12:32:47.785: E/AndroidRuntime(276): Caused by: java.lang.NullPointerException
07-26 12:32:47.785: E/AndroidRuntime(276): at com.example.massar_parent.MainActivity.onCreate(MainActivity.java:44)
07-26 12:32:47.785: E/AndroidRuntime(276): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
07-26 12:32:47.785: E/AndroidRuntime(276): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
還有MainActivity.java中的代碼
import android.os.Bundle;
import android.os.StrictMode;
import android.util.Log;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;
public class MainActivity extends Activity {
//private TextView texte = null;
TextView txt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txt.setText("Connexion...");
// Appeler la méthode pour récupérer les données JSON
txt.setText(getServerData(strURL));
}
// Mettre l'adresse du script PHP
// Attention localhost ou 127.0.0.1 ne fonctionnent pas. Mettre l'adresse IP
// local.
public static final String strURL = "http://localhost/massar/connection.php";
private String getServerData(String returnString) {
InputStream is = null;
String result = "";
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("NomEleve", "L"));
// Envoie de la commande http
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(strURL);
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection " + e.toString());
}
// Convertion de la requête en string
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
// Parse les données JSON
try {
JSONArray jArray = new JSONArray(result);
for (int i = 0; i < jArray.length(); i++) {
JSONObject json_data = jArray.getJSONObject(i);
// Affichage ID_ville et Nom_ville dans le LogCat
Log.i("log_tag", "CNE: " + json_data.getInt("CNE") + ", NomEleve: "
+ json_data.getString("NomEleve"));
// Résultats de la requête
returnString += "\n\t" + jArray.getJSONObject(i);
}
} catch (JSONException e) {
Log.e("log_tag", "Error parsing data " + e.toString());
}
return returnString;
}
}
這是代碼AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.massar_parent"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="21" />
<uses-permission android:name="android.permission.INTERNET"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
我希望有人能幫幫忙 :/
我可以看到兩個錯誤:
findViewById()
嗎? 您有一個字段txt
:
TextView txt;
已聲明,但從未設置為值。 因此,當您嘗試在此處使用它時:
txt.setText("Connexion...");
它會引發異常,因為它仍然具有null
。
如果您在布局中聲明了TextView(例如,使用<TextView android:id="@+id/the_identifier_of_your_textview"
),則需要在調用setContentView
之后立即像這樣分配它:
txt = (TextView)this.FindViewById(R.id.the_identifier_of_your_textview);
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.