CODEWITHSUNDEEP
javaandroidthisandroid-context
Denis Balan
Denis Balan

Reputation: 198

Android application context param

I have a packed library .jar, and I want to access one class from it.
but in param this need Context, I am new in android dev). Tried to pass (this) on MainActivity, but result is null. Can you explain why is this happening and how to fix?

Here is sample code:

Context paramContext = this;
    ApiHttpClient localApiHttpClient = (ApiHttpClient)paramContext.getSystemService("com.vine.api.ApiHttpClient");
    if (localApiHttpClient == null)
      localApiHttpClient = (ApiHttpClient)paramContext.getApplicationContext().getSystemService("com.vine.api.ApiHttpClient");
    if (localApiHttpClient == null)
        Log.d("loadState", "Result is null");

log:

06-04 10:57:44.502: E/AndroidRuntime(6610): FATAL EXCEPTION: main
06-04 10:57:44.502: E/AndroidRuntime(6610): java.lang.ExceptionInInitializerError
06-04 10:57:44.502: E/AndroidRuntime(6610):     at java.lang.Class.classForName(Native Method)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at java.lang.Class.forName(Class.java:217)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at java.lang.Class.forName(Class.java:172)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at com.example.dfgdf.MainActivity.onCreate(MainActivity.java:59)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.app.Activity.performCreate(Activity.java:5008)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2211)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.app.ActivityThread.access$600(ActivityThread.java:143)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1209)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.os.Looper.loop(Looper.java:137)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at android.app.ActivityThread.main(ActivityThread.java:4965)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at java.lang.reflect.Method.invokeNative(Native Method)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at java.lang.reflect.Method.invoke(Method.java:511)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at dalvik.system.NativeStart.main(Native Method)
06-04 10:57:44.502: E/AndroidRuntime(6610): Caused by: java.lang.NullPointerException
06-04 10:57:44.502: E/AndroidRuntime(6610):     at com.vine.android.vineApplication.getHttpUserAgent(Unknown Source)
06-04 10:57:44.502: E/AndroidRuntime(6610):     at com.vine.api.ApiHttpClient.(Unknown Source)

Upvotes: 0

Views: 498

Answers (1)

Dmitry Nelepov
Dmitry Nelepov

Reputation: 7306

Hm, may be you need add your JAR to ClassLoader and then make Class.forName like on Java do.

Here example 

public static ClassLoader loadExternalJar(File file) throws Exception {
        if (file.exists()) {
            Method method = URLClassLoader.class.getDeclaredMethod("addURL", new Class[]{URL.class});
            method.setAccessible(true);
            ClassLoader retClassLoader;

            retClassLoader = Thread.currentThread().getContextClassLoader();

            method.invoke(retClassLoader, new Object[]{file.toURI().toURL()});
            return retClassLoader;
        } else {
            throw new Exception("File not found with JAR:"+file.getAbsolutePath());
        }
    }

And then try call Class.forName("com.vine.api.ApiHttpClient")

Try this:

 try {
        Class<?> someApiClass = Class.forName("com.vine.api.ApiHttpClient");
        if (someApiClass != null) {
            ApiHttpClient localApiHttpClient = (ApiHttpClient) someApiClass
                    .newInstance();
            if (localApiHttpClient != null) {
                // TODO Oeprations
                Log.d("loadState", "Result is Good");
            } else {
                Log.d("loadState", "Result is null");
            }
        }
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InstantiationException e) {
        e.printStackTrace();
    }

Upvotes: 2

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