这个问题在这里已有答案：
我正在尝试使用Volley并在登录后发送GET请求来检查数据。 我有特殊级别的'API'，所有的Volley员工都在这里。 我想要做的是在LoginActivity中检查验证后（默认的android studio模板）我想在LoginActivity中创建API实例并向服务器发送GET请求。 这仅用于测试Volley，后来我想在一些Main类中创建一个API实例。
这是我的API类：
import android.app.Application;
import android.util.Log;
import com.android.volley.*;
import com.android.volley.toolbox.Volley;
import com.android.volley.toolbox.JsonObjectRequest;
import org.json.JSONObject;
import java.lang.String;
public class API extends Application {
protected String ServerURL;
protected String GET;
protected String POST;
protected RequestQueue queue;
public API(){
setServerURL("http://localhost:63424");
setGET("http://localhost:63424/api");
setPOST("http://localhost:63424/api");
queue = Volley.newRequestQueue(this);
}
protected void SendGET (String request)
{
JsonObjectRequest getRequest = new JsonObjectRequest(Request.Method.GET, request, null,
new Response.Listener<JSONObject>()
{
@Override
public void onResponse(JSONObject response) {
// display response
Log.d("ResponseAPI", response.toString());
}
},
new Response.ErrorListener()
{
@Override
public void onErrorResponse(VolleyError error) {
Log.d("Error.ResponseAPI", error.toString());
}
}
);
queue.add(getRequest);
}
//Logowanie
public boolean CheckLogin (String Login, String Password){
setGET(getGET()+"/Search_Users_/login=/"+Login + "/");
SendGET(getGET());
return true;
}
public String getServerURL() {
return ServerURL;
}
public void setServerURL(String ServerURL) {
ServerURL = ServerURL;
}
public String getGET() {
return GET;
}
public void setGET(String GET) {
this.GET = GET;
}
public String getPOST() {
return POST;
}
public void setPOST(String POST) {
this.POST = POST;
}
}
在这里，我尝试在LoginActivity中创建API实例：
public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {
private final String mEmail;
private final String mPassword;
UserLoginTask(String email, String password) {
mEmail = email;
mPassword = password;
}
@Override
protected Boolean doInBackground(Void... params) {
// TODO: attempt authentication against a network service.
try {
// Simulate network access.
Thread.sleep(2000);
} catch (InterruptedException e) {
return false;
}
Log.d("API", "Zaraz utworze API");
API api = new API();
return api.CheckLogin(mEmail, mPassword);
// TODO: register the new account here.
}
@Override
protected void onPostExecute(final Boolean success) {
mAuthTask = null;
showProgress(false);
if (success) {
finish();
} else {
mPasswordView.setError(getString(R.string.error_incorrect_password));
mPasswordView.requestFocus();
}
}
@Override
protected void onCancelled() {
mAuthTask = null;
showProgress(false);
}
}
这个解决方案不起作用，我收到一个错误：
FATAL EXCEPTION: AsyncTask #1
Process: pawel.cooker, PID: 2646
java.lang.RuntimeException: An error occurred while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:353)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
at java.util.concurrent.FutureTask.run(FutureTask.java:271)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
at java.lang.Thread.run(Thread.java:764)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.File android.content.Context.getCacheDir()' on a null object reference
at android.content.ContextWrapper.getCacheDir(ContextWrapper.java:256)
at com.android.volley.toolbox.Volley.newRequestQueue(Volley.java:43)
at com.android.volley.toolbox.Volley.newRequestQueue(Volley.java:78)
at pawel.cooker.API.<init>(API.java:17)
at pawel.cooker.LoginActivity$UserLoginTask.doInBackground(LoginActivity.java:320)
at pawel.cooker.LoginActivity$UserLoginTask.doInBackground(LoginActivity.java:299)
at android.os.AsyncTask$2.call(AsyncTask.java:333)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
at java.lang.Thread.run(Thread.java:764)
Volley有问题，但不知道出了什么问题。
Volley存在问题
不，您的API类存在问题。
确保将其放入清单中
<application
android:name=".API"
之后
onCreate。或者，不要使用Application，并使用Volley-scoped singleton - see example from documentationlocalhost替换为实际的服务器地址public class API extends Application {
public static final String ServerURL = "http://<Use real server here>:63424";
public static final String GET = ServerURL+"/api";
public static final String POST = ServerURL+"/api";
protected RequestQueue queue;
private final API mInstance;
private API() { }
public API getInstance() {
return mInstance;
}
@Override
public void onCreate(){
super.onCreate();
mInstance = this;
queue = Volley.newRequestQueue(this);
}
return阻止Async函数的值。使用回调来传回结果protected void sendGET (String url, Response.Listener<JSONObject> onSuccess)
{
JsonObjectRequest getRequest = new JsonObjectRequest(Request.Method.GET, url, null,
onSuccess,
new Response.ErrorListener()
{
@Override
public void onErrorResponse(VolleyError error) {
Log.d("Error.ResponseAPI", error.toString());
}
}
);
queue.add(getRequest);
}
public void checkLogin (String Login, Response.Listener<JSONObject> onSuccess){
SendGET(GET+"/Search_Users_/login=/"+Login, onSuccess);
}
new API()或使用上面的实现时，不要使用((API) getApplicationContext())，API.getInstance()例如，
API api = API.getInstance();
api.checkLogin(mEmail, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
// TODO: register the new account here.
}
});
在相关的说明中，如果您使用的是RESTful API，那么Retrofit可能会更有用