Java Android截击无法返回字符串
我已经创建了一个类，通过它我想从数据库中获取一个列表url。但我得到了这个错误：Java Android截击无法返回字符串,java,android,Java,Android,我已经创建了一个类，通过它我想从数据库中获取一个列表url。但我得到了这个错误： 03-30 15:05:35.599 3591-3591/? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.imran.myapp, PID: 3591
03-30 15:05:35.599 3591-3591/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.imran.myapp, PID: 3591
java.lang.NullPointerException: Attempt to read from null array
at com.example.imran.myapp.gridgallery.onCreateView(gridgallery.java:55)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1026)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1207)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1572)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:493)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6145)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
03-30 15:05:35.599 1032-1045/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-30 15:05:35.599 1032-1045/? W/ActivityManager: Force finishing activity com.example.imran.myapp/.Home
03-30 15:05:35.609 1032-1045/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-30 15:05:35.909 1032-1032/? D/CrashAnrDetector: processName: com.example.imran.myapp
03-30 15:05:35.919 1032-1032/? D/CrashAnrDetector: broadcastEvent : com.example.imran.myapp data_app_crash
03-30 15:05:36.159 1032-1059/? W/ActivityManager: Activity pause timeout for ActivityRecord{3f2af340 u0 com.example.imran.myapp/.Home t3125 f}
03-30 15:05:37.019 1032-1521/? I/WindowState: WIN DEATH: Window{224e112b u0 com.example.imran.myapp/com.example.imran.myapp.Home}
03-30 15:05:37.079 1032-1528/? I/ActivityManager: Process com.example.imran.myapp (pid 3591)(adj 9) has died(67,606)
03-30 15:05:37.359 10199-10199/? D/AASAservice-UpdateReceiver: AASAUpdateReceiver: android.intent.action.PACKAGE_REPLACED, package = com.example.imran.myapp, uid = -1
03-30 15:05:37.379 2433-3619/? D/PkgBroadcastIntentOp: Received broadcast action=android.intent.action.PACKAGE_REPLACED and uri=com.example.imran.myapp
03-30 15:05:37.559 2433-3974/? D/k: Processing package: com.example.imran.myapp
03-30 15:05:37.559 2227-3976/? D/Compatibility: intentservice saw: Intent { act=android.intent.action.PACKAGE_REPLACED dat=package:com.example.imran.myapp flg=0x4000010 cmp=com.sec.android.app.soundalive/.compatibility.Compatibility$Receiver (has extras) } Bundle[{android.intent.extra.UID=10252, android.intent.extra.REPLACING=true, android.intent.extra.user_handle=0}]
03-30 15:05:37.589 2433-3974/? D/GassUtils: Found app info for package com.example.imran.myapp:1. Hash: 6b9333e031907d7a6a6c12cd9fdfa0d23bd13ee0f40c9617ddd005dc358321b0
03-30 15:05:37.589 2433-3974/? D/k: Found info for package com.example.imran.myapp in db.
gridgallery.javapublic View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_gridgallery, null);
Myserver myserver = new Myserver();
//postStringRequest(myserver.url + "/api/albums/getalbums.php", view);
AlbumsList albumsList = new AlbumsList(myserver.url+"/api/albums/getalbums.php",getContext(),view);
albumsList.connection(); // Do connection
Toast.makeText(getContext(),albumsList.imgsurls[1],Toast.LENGTH_LONG).show();
/*
GridView gv = (GridView)view.findViewById(R.id.fragment_gridgallery);
ImageAdapter myadapter = new ImageAdapter(getContext(),albumsList.imgurls());
gv.setAdapter(myadapter);
*/
return view;
}
public class AlbumsList {
private String server;
Context mycontext;
public String[] imgsurls;
private View view;
AlbumsList(String serverurl, Context c,View uview){
mycontext = c;
server = serverurl;
view = uview;
}
public View connection(){
// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(mycontext);
// Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.POST, server,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
//GridView gv = (GridView)view.findViewById(R.id.fragment_gridgallery);
final ArrayList<String> urls2 = new ArrayList<String>();
try {
JSONArray jsonObj = new JSONArray(response);
Myserver myserver = new Myserver();
for (int i=0;i<jsonObj.length();i++){
JSONObject c = jsonObj.getJSONObject(i);
String imgurl = myserver.url+"/images/thumbs/tn_"+c.getString("album_thumbnail");
urls2.add(imgurl);
}
final String myabc[] = urls2.toArray(new String[urls2.size()]); //Do not remove this
imgsurls = myabc;
Toast.makeText(mycontext, imgsurls[0], Toast.LENGTH_LONG).show(); //Interestingly this toast works and imgsurls[] is ok
} catch (JSONException e) {
e.printStackTrace();
Toast.makeText(mycontext,e.getLocalizedMessage(),Toast.LENGTH_LONG).show();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(mycontext, "Unable to reach server", Toast.LENGTH_LONG).show();
}
}) {
@Override
protected Map<String, String> getParams() {
Map<String, String> params = new HashMap<String, String>();
params.put("getalbum", "getalbum");
return params;
}
};
queue.add(stringRequest);
return view;
}
public String[] imgurls(){
return imgsurls;
}
}
AlbumsList.javapublic View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_gridgallery, null);
Myserver myserver = new Myserver();
//postStringRequest(myserver.url + "/api/albums/getalbums.php", view);
AlbumsList albumsList = new AlbumsList(myserver.url+"/api/albums/getalbums.php",getContext(),view);
albumsList.connection(); // Do connection
Toast.makeText(getContext(),albumsList.imgsurls[1],Toast.LENGTH_LONG).show();
/*
GridView gv = (GridView)view.findViewById(R.id.fragment_gridgallery);
ImageAdapter myadapter = new ImageAdapter(getContext(),albumsList.imgurls());
gv.setAdapter(myadapter);
*/
return view;
}
public class AlbumsList {
private String server;
Context mycontext;
public String[] imgsurls;
private View view;
AlbumsList(String serverurl, Context c,View uview){
mycontext = c;
server = serverurl;
view = uview;
}
public View connection(){
// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(mycontext);
// Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.POST, server,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
//GridView gv = (GridView)view.findViewById(R.id.fragment_gridgallery);
final ArrayList<String> urls2 = new ArrayList<String>();
try {
JSONArray jsonObj = new JSONArray(response);
Myserver myserver = new Myserver();
for (int i=0;i<jsonObj.length();i++){
JSONObject c = jsonObj.getJSONObject(i);
String imgurl = myserver.url+"/images/thumbs/tn_"+c.getString("album_thumbnail");
urls2.add(imgurl);
}
final String myabc[] = urls2.toArray(new String[urls2.size()]); //Do not remove this
imgsurls = myabc;
Toast.makeText(mycontext, imgsurls[0], Toast.LENGTH_LONG).show(); //Interestingly this toast works and imgsurls[] is ok
} catch (JSONException e) {
e.printStackTrace();
Toast.makeText(mycontext,e.getLocalizedMessage(),Toast.LENGTH_LONG).show();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(mycontext, "Unable to reach server", Toast.LENGTH_LONG).show();
}
}) {
@Override
protected Map<String, String> getParams() {
Map<String, String> params = new HashMap<String, String>();
params.put("getalbum", "getalbum");
return params;
}
};
queue.add(stringRequest);
return view;
}
public String[] imgurls(){
return imgsurls;
}
}
公共类相册列表{
私有字符串服务器；
语境；
公共字符串[]imgsurls；
私人视野；
AlbumsList（字符串服务器URL、上下文c、视图uview）{
mycontext=c；
server=serverurl；
视图=uview；
}
公共视图连接（）{
//实例化RequestQueue。
RequestQueue=Volley.newRequestQueue（mycontext）；
//从提供的URL请求字符串响应。
StringRequest StringRequest=新的StringRequest（Request.Method.POST，服务器，
新的Response.Listener（）{
@凌驾
公共void onResponse（字符串响应）{
//GridView gv=（GridView）view.findViewById（R.id.fragment\u gridgallery）；
最终ArrayList urls2=新ArrayList（）；
试一试{
JSONArray jsonObj=新JSONArray（响应）；
Myserver Myserver=新的Myserver（）；
对于（inti=0；i，因为Volley
请求是异步的
因此，当您调用albumsList.connection（）；
时，请求在后台运行，在完成之前，控制将转到以下行：
Toast.makeText(getContext(),albumsList.imgsurls[1],Toast.LENGTH_LONG).show();
此时，您的请求尚未完成。Volley以异步方式工作。这意味着它不会立即返回操作结果。您正在尝试在从服务器获取结果之前访问结果
当结果实际交付时，您应该将视图初始化逻辑移动到onResponse（）
。您是说我应该在onResponse（）中初始化String[]imgsurls
？是的。当收到imgresponse时，然后在那里初始化imgurls，使其首先成为私有类成员变量。然后在从OnResponseAnks传递控制以获得答复时，在toast中使用它。您能给出一个如何克服此问题的想法吗？请在Volley的onResponse
上使用imgurls
这就是你说的吗？是的，你可以这样做。