Issue
I previously developed a real time currency converter program, and would like to export it as an Android app.
To do so, I am using a GET request with RestTemplate to get the rate between 2 currencies. However, I then get this error: android.os.NetworkOnMainThreadException
Here is the code I first tried:
public void displayResult(View view) {
TextView output = (TextView) findViewById(R.id.conversion);
output.setInputType(InputType.TYPE_CLASS_NUMBER);
output.setText(String.valueOf(convert()));
}
float convert() {
EditText textBaseCurrency = (EditText) findViewById(R.id.BASE_CURRENCY);
EditText textTargetCurrency = (EditText) findViewById(R.id.TARGET_CURRENCY);
EditText textAmount = (EditText) findViewById(R.id.AMOUNT);
String baseCurrency = textBaseCurrency.getText().toString().toUpperCase();
String targetCurrency = textTargetCurrency.getText().toString().toUpperCase();
float amount = Integer.parseInt(textAmount.getText().toString());
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
String url = "https://v6.exchangerate-api.com/v6/" + API_KEY + "/latest/" + baseCurrency;
ResponseEntity<String> responseEntity = restTemplate.getForEntity(url, String.class);
System.out.println(responseEntity);
ObjectMapper mapper = new ObjectMapper();
JsonNode root = null;
try {
root = mapper.readTree(responseEntity.getBody());
} catch (IOException e) {
e.printStackTrace();
}
JsonNode name = root.get(conversionRates);
JsonNode rates = name.get(targetCurrency);
float rate = rates.floatValue();
float newAmount = rate * amount;
return newAmount;
}
I saw that the solution would be to use AsyncTask
. I tried it, but I wasn't successful:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Connection().execute();
}
public class Connection extends AsyncTask<Void, Void, Void> {
@Override
protected Void doInBackground(Void... voids) {
EditText textBaseCurrency = (EditText) findViewById(R.id.BASE_CURRENCY);
EditText textTargetCurrency = (EditText) findViewById(R.id.TARGET_CURRENCY);
EditText textAmount = (EditText) findViewById(R.id.AMOUNT);
String baseCurrency = textBaseCurrency.getText().toString().toUpperCase();
String targetCurrency = textTargetCurrency.getText().toString().toUpperCase();
float amount = Integer.parseInt(textAmount.getText().toString());
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
String url = "https://v6.exchangerate-api.com/v6/" + API_KEY + "/latest/" + baseCurrency;
ResponseEntity<String> responseEntity = restTemplate.getForEntity(url, String.class);
System.out.println(responseEntity);
ObjectMapper mapper = new ObjectMapper();
JsonNode root = null;
try {
root = mapper.readTree(responseEntity.getBody());
} catch (IOException e) {
e.printStackTrace();
}
JsonNode name = root.get(conversionRates);
JsonNode rates = name.get(targetCurrency);
float rate = rates.floatValue();
float newAmount = rate * amount;
return null;
}
Moreover, this is now deprecated.
My gradle.build file:
packagingOptions{
exclude 'META-INF/notice.txt'
exclude 'META-INF/license.txt'
}dependencies {
implementation fileTree(dir: "libs", include: ["*.jar"])
implementation 'androidx.appcompat:appcompat:1.2.0'
implementation 'androidx.constraintlayout:constraintlayout:2.0.1'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test.ext:junit:1.1.2'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
implementation 'com.fasterxml.jackson.core:jackson-databind:2.9.10.6'
implementation 'javax.xml.stream:stax-api:1.0'
implementation 'org.springframework.android:spring-android-rest-template:1.0.1.RELEASE'
}
I also added <uses-permission android:name="android.permission.INTERNET" />
in my AndroidManifest.xml
Solution
You can use some library like to do this:
but first of all you should add this permission:
<uses-permission android:name="android.permission.INTERNET" />
but the easiest way is :
class RequestTask extends AsyncTask<String, String, String>{
@Override
protected String doInBackground(String... uri) {
HttpClient httpclient = new DefaultHttpClient();
HttpResponse response;
String responseString = null;
try {
response = httpclient.execute(new HttpGet(uri[0]));
StatusLine statusLine = response.getStatusLine();
if(statusLine.getStatusCode() == HttpStatus.SC_OK){
ByteArrayOutputStream out = new ByteArrayOutputStream();
response.getEntity().writeTo(out);
responseString = out.toString();
out.close();
} else{
//Closes the connection.
response.getEntity().getContent().close();
throw new IOException(statusLine.getReasonPhrase());
}
} catch (ClientProtocolException e) {
//TODO Handle problems..
} catch (IOException e) {
//TODO Handle problems..
}
return responseString;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
//Do anything with response..
}
}
You then can make a request by:
new RequestTask().execute("https://v6.exchangerate-api.com/v6/" + API_KEY + "/latest/" + baseCurrency);
keep in mind if you use this application on android 9 you should use this attribute to your AndroidManifest.xml where you allow all http for all requests:
<application android:usesCleartextTraffic="true">
</application>
But in case you want some more configurations for different links, for instance, allowing HTTP for some domains but not other domains you must provide res/xml/networkSecurityConfig.xml
file.
To do this in Android 9 Pie you will have to set a networkSecurityConfig in your Manifest application tag like this:
<?xml version="1.0" encoding="utf-8"?>
<manifest ... >
<application android:networkSecurityConfig="@xml/network_security_config">
</application>
</manifest>
Then in your xml
folder you now have to create a file named network_security_config
just like the way you have named it in the Manifest and from there the content of your file should be like this to enable all requests without encryptions:
<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
<base-config cleartextTrafficPermitted="true">
<trust-anchors>
<certificates src="system" />
</trust-anchors>
</base-config>
</network-security-config>
but note this:
HttpClient
is not supported any more in sdk 23. You have to use URLConnection
or downgrade to sdk 22 (compile 'com.android.support:appcompat-v7:22.2.0'
)
If you need sdk 23, add this to your gradle:
android {
useLibrary 'org.apache.http.legacy'
}
You also may try to download and include HttpClient.jar directly into your project or use OkHttp instead
Answered By - Hassan Yousefzadeh
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