凌空请求队列 NullPointerException
Volley Request Queue NullPointerException
我正在尝试使用 Volley 库通过用户通过 SearchWidget
提供的搜索查询在网络上查询 xml api。
每当我输入搜索字符串时,应用程序都会在将 StringRequest
添加到 RequestQueue
时崩溃并显示 NullPointerException
。
为什么会这样?
我已经按照 Android Developer Guide.
中的建议使用单例模式的 Volley
这是我在 MainActivity
中的 search()
函数。
public static final String TAG = "MYAPPTAG"
private RequestQueue mRequestQueue;
...
protected void onCreate(Bundle savedInstanceState) {
...
// Handle search intent
Intent intent = getIntent();
if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
String query = intent.getStringExtra(SearchManager.QUERY);
search(query);
}
volley = MySingleton.getInstance(getApplicationContext());
mRequestQueue = volley.getRequestQueue();
}
...
private void search(String query) {
String xml = null;
String url = "http://www.acme.com/example.php?query=" + query;
StringRequest stringRequest = new StringRequest(Request.Method.POST, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
}
);
stringRequest.setTag(TAG);
mRequestQueue
.add(stringRequest); // the exception fires here
}
...
查看下面的堆栈跟踪。
02-22 23:08:50.636 9856-9856/com.example.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.app, PID: 9856
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.app/com.example.app.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2212)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5146)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.app.MainActivity.search(MainActivity.java:121)
at com.example.app.MainActivity.onCreate(MainActivity.java:83)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5146)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
at dalvik.system.NativeStart.main(Native Method)
在从单例设置请求队列之前,您正在启动搜索。
因此,在创建时,您先检查 Intent,然后开始搜索,然后再处理 volley 单例,然后再处理请求队列。尝试在 Intent 检查之前移动 volley 代码,如下所示:
volley = MySingleton.getInstance(getApplicationContext());
mRequestQueue = volley.getRequestQueue();
Intent intent = getIntent();
if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
String query = intent.getStringExtra(SearchManager.QUERY);
search(query);
}
我正在尝试使用 Volley 库通过用户通过 SearchWidget
提供的搜索查询在网络上查询 xml api。
每当我输入搜索字符串时,应用程序都会在将 StringRequest
添加到 RequestQueue
时崩溃并显示 NullPointerException
。
为什么会这样?
我已经按照 Android Developer Guide.
中的建议使用单例模式的 Volley这是我在 MainActivity
中的 search()
函数。
public static final String TAG = "MYAPPTAG"
private RequestQueue mRequestQueue;
...
protected void onCreate(Bundle savedInstanceState) {
...
// Handle search intent
Intent intent = getIntent();
if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
String query = intent.getStringExtra(SearchManager.QUERY);
search(query);
}
volley = MySingleton.getInstance(getApplicationContext());
mRequestQueue = volley.getRequestQueue();
}
...
private void search(String query) {
String xml = null;
String url = "http://www.acme.com/example.php?query=" + query;
StringRequest stringRequest = new StringRequest(Request.Method.POST, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
}
);
stringRequest.setTag(TAG);
mRequestQueue
.add(stringRequest); // the exception fires here
}
...
查看下面的堆栈跟踪。
02-22 23:08:50.636 9856-9856/com.example.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.app, PID: 9856
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.app/com.example.app.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2212)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5146)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.app.MainActivity.search(MainActivity.java:121)
at com.example.app.MainActivity.onCreate(MainActivity.java:83)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5146)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
at dalvik.system.NativeStart.main(Native Method)
在从单例设置请求队列之前,您正在启动搜索。
因此,在创建时,您先检查 Intent,然后开始搜索,然后再处理 volley 单例,然后再处理请求队列。尝试在 Intent 检查之前移动 volley 代码,如下所示:
volley = MySingleton.getInstance(getApplicationContext());
mRequestQueue = volley.getRequestQueue();
Intent intent = getIntent();
if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
String query = intent.getStringExtra(SearchManager.QUERY);
search(query);
}