我在主nullpointer异常时遇到致命异常错误。基本上我有2个活动登录和主要活动。你将在登录活动中输入app key和app secret然后在认证后它将带你到主活动任何帮助？
登录活动
public class login_activity extends AppCompatActivity {
public String APP_kEY ;
public String APP_SECRET;
public String accessToken;
EditText app_key_view;
EditText App_secret_view;
Button dropbox;
public DropboxAPI<AndroidAuthSession> mDBApi;
@Override
protected void onCreate(Bundle savedInstanceState) {
SharedPreferences pref = getSharedPreferences("login",MODE_PRIVATE);
APP_kEY = pref.getString("appkey",null);
APP_SECRET = pref.getString("appsecret",null);
accessToken = pref.getString("access",null);
if (accessToken != null){
AppKeyPair appkeys = new AppKeyPair(APP_kEY,APP_SECRET);
AndroidAuthSession session = new AndroidAuthSession(appkeys);
session.setOAuth2AccessToken(accessToken);
Intent i = new Intent(login_activity.this,MainActivity.class);
startActivity(i);
finish();
}
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login_activity);
app_key_view=(EditText)findViewById(R.id.app_key_text);
App_secret_view=(EditText)findViewById(R.id.app_secret_text);
dropbox = (Button)findViewById(R.id.link_dropbox);
//////////////////////////////////////////////////////////////
dropbox.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
APP_kEY = app_key_view.getText().toString();
APP_SECRET = App_secret_view.getText().toString();
AppKeyPair appKeys = new AppKeyPair(APP_kEY,APP_SECRET);
AndroidAuthSession session = new AndroidAuthSession(appKeys);
mDBApi = new DropboxAPI<>(session);
mDBApi.getSession().startOAuth2Authentication(login_activity.this);
}
});
}
@Override
protected void onResume () {
super.onResume();
if(mDBApi.getSession().authenticationSuccessful()){
try {
mDBApi.getSession().finishAuthentication();
accessToken = mDBApi.getSession().getOAuth2AccessToken();
SharedPreferences.Editor editor = getSharedPreferences("login",MODE_PRIVATE).edit();
editor.putString("appkey",APP_kEY);
editor.putString("appsecret",APP_SECRET);
editor.putString("access",accessToken);
editor.commit();
Intent i = new Intent(login_activity.this,MainActivity.class);
startActivity(i);
finish();
}
catch (IllegalStateException e){
Log.i("DbAuthLog", "Error authenticationg", e);
}
}
}
logcat的
09-11 21:06:01.947 3842-3842/? I/art﹕ Late-enabling -Xcheck:jni
09-11 21:06:01.975 3842-3851/? I/art﹕ Debugger is no longer active
09-11 21:06:02.370 3842-3857/? I/art﹕ Background sticky concurrent mark sweep GC freed 2909(253KB) AllocSpace objects, 2(32KB) LOS objects, 0% free, 50MB/50MB, paused 36.891ms total 133.660ms
09-11 21:06:02.803 3842-3842/? D/AndroidRuntime﹕ Shutting down VM
09-11 21:06:02.803 3842-3842/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.ayzaz.timescopev1.timescope, PID: 3842
java.lang.RuntimeException: Unable to resume activity {com.example.ayzaz.timescopev1.timescope/com.example.ayzaz.timescopev1.timescope.login_activity}: java.lang.NullPointerException: Attempt to invoke virtual method 'com.dropbox.client2.session.Session com.dropbox.client2.DropboxAPI.getSession()' on a null object reference
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2986)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3017)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
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:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'com.dropbox.client2.session.Session com.dropbox.client2.DropboxAPI.getSession()' on a null object reference
at com.example.ayzaz.timescopev1.timescope.login_activity.onResume(login_activity.java:77)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1257)
at android.app.Activity.performResume(Activity.java:6076)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2975)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3017)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
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:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
09-11 21:06:05.849 3842-3842/com.example.ayzaz.timescopev1.timescope I/Process﹕ Sending signal. PID: 3842 SIG: 9
答案 0 :(得分：0)
getline(cin,*(employees[i].children[j].name));
之后调用{p> onResume()。
onCreate()开始时，onResume()为mDBApi，因为此字段仅在null方法中分配。
您需要直接在onClick()分配mDBApi，或者在尝试使用之前需要检查它是否为onCreate()。