Android Studio php connection

Question

我试图在android studio java中使用php从db获取信息。php代码工作100%。问题是，当我从Android模拟器打开应用程序时，应用程序几乎立即关闭。

--------- beginning of crash
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.c__expensechart, PID: 2450
java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:121)
at org.json.JSONTokener.nextValue(JSONTokener.java:98)
at org.json.JSONObject.<init>(JSONObject.java:165)
at org.json.JSONObject.<init>(JSONObject.java:182)
at com.example.c__expensechart.MainActivity$Connection.onPostExecute(MainActivity.java:89)
at com.example.c__expensechart.MainActivity$Connection.onPostExecute(MainActivity.java:57)
at android.os.AsyncTask.finish(AsyncTask.java:771)
at android.os.AsyncTask.access$900(AsyncTask.java:199)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:788)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
I/Process: Sending signal. PID: 2450 SIG: 9

这是我在run中得到的错误信息Logcat是空的构建也没有错误吗从我看到的onPostExecute中有一个问题让我给你们展示一下它的样子

我有一个类

class Connection extends AsyncTask<String, String, String>

里面有两个函数:

protected String doInBackground(String... params){
String result = "";
String host = "http://192.168.1.114/php_api/GET.php";
try{
HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet();
request.setURI(new URI(host));
HttpResponse response = client.execute(request);
BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
StringBuffer stringBuffer = new StringBuffer("");
String line = "";
while((line = reader.readLine()) != null){
stringBuffer.append(line);
break;
}
reader.close();
result = stringBuffer.toString();
}
catch(Exception e){
return new String("There exception" + e.getMessage());
}
return null;
}

和

protected void onPostExecute(String result){
try {
JSONObject jsonResult = new JSONObject(result);
int success = jsonResult.getInt("success");
if(success == 1){
JSONArray measurements = jsonResult.getJSONArray("measurements");
for(int i = 0; i < measurements.length(); i++){
JSONObject measure = measurements.getJSONObject(i);
int measureId = measure.getInt("id");
double start_times = measure.getDouble("start_times");
double end_times = measure.getDouble("end_times");
double power = measure.getDouble("power");
String line = measureId + ":" + start_times + ":" + end_times + ":" + power;
setMeasureInfo(line);
}
}else{
Toast.makeText(getApplicationContext(), "There aren't any measurements", Toast.LENGTH_SHORT).show();
}
}
catch (JSONException e){
}
}

编辑:关于db连接，我做了它，所以它显示了我在文件中读取的所有内容，只是为了确保这就是

{"success":1,
"measurements"[
{"id":"1","start_times":"42405","end_times":"48","power":"65508"}
]}

我的PHP代码:

<?php
$host = 'localhost';
$user = 'root';
$pwd = '';
$db = 'c--db';
$conn = mysqli_connect($host, $user, $pwd, $db);
if(!$conn){
die("ERROR in connection: " . mysqli_connect_error());
}
$response = array();
$sql_query = "SELECT * FROM `measurements`";
$result = mysqli_query($conn, $sql_query);
if(mysqli_num_rows($result) > 0){
$response['success'] = 1;
$measurements = array();
while($row = mysqli_fetch_assoc($result)){
array_push($measurements, $row);
}
$response['measurements'] = $measurements;
}else{
$response['success'] = 0;
$response['message'] =  'No data';
}
echo json_encode($response);
mysqli_close($conn);
?>

Answer 1

java.lang。NullPointerException:尝试在空对象引用上调用虚拟方法'int java.lang.String.length()'

com.example.c__expensechart.MainActivity Connection.onPostExecute美元(MainActivity.java: 89)

JSONArray measurements = jsonResult.getJSONArray("measurements");
for(int i = 0; i < measurements.length(); i++){
...
}

你可能没有在这里检索你的数组。检查键是否正确

Answer 2

我解决了这个问题。所以实际上我仔细检查了错误日志，发现它与apache库有关我搜索了错误，发现我不得不将其添加到AndroidManifest.xml中它应该看起来像这样:

<application
...
...
android:usesCleartextTraffic="true"
android:requestLegacyExternalStorage="true">
...
...
<uses-library
android:name="org.apache.http.legacy"
android:required="false" />
</application>