Android：在进行其他活动之前先销毁活动

Question

I have two activity in my android application :
1. LoginActivity : User can Login or
2. MainActivity : Showing user current location on map

Scenario :
1. User login as guest
2. Go to Main Activity . (No NPE here)
3. User took some action that needed to login
4. Intent to LoginActivity
5. I need to destroy MainActivity before directing user to LoginActivity
6. User input username and password on LoginActivity
7. If user exist and password true go to MainActivity
8. NPE (or Null Pointer Exception) happened here.

So, in my case, i needed to destroy MainActivity (Point number 5) before directing user to LoginActivity. I've tried this :

final AlertDialog.Builder builder = new AlertDialog.Builder(context);

final String message = getResources().getString(R.string.NCI);

builder.setMessage(Html.fromHtml("To do your action, we need you to logged in our server"))
.setTitle("LOGIN REQUIRED")
.setPositiveButton("OK",
    new OnClickListener(){
        public void onClick(DialogInterface d, int id){                         
            Intent i = new Intent(MainActivity.this, LoginActivity.class);

            i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
            startActivity(i);
            finish();
        }
    }
);

builder.create().show();

Log Cat

07-25 16:04:27.287: E/AndroidRuntime(19823): FATAL EXCEPTION: main
07-25 16:04:27.287: E/AndroidRuntime(19823): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.yai.properti.tujuh.tujuh.tujuh/com.yai.properti.tujuh.tujuh.tujuh.MainActivity}: java.lang.NullPointerException
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2122)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.app.ActivityThread.access$600(ActivityThread.java:140)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1228)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.os.Looper.loop(Looper.java:137)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.app.ActivityThread.main(ActivityThread.java:4895)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at java.lang.reflect.Method.invokeNative(Native Method)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at java.lang.reflect.Method.invoke(Method.java:511)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:994)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at dalvik.system.NativeStart.main(Native Method)
07-25 16:04:27.287: E/AndroidRuntime(19823): Caused by: java.lang.NullPointerException
07-25 16:04:27.287: E/AndroidRuntime(19823):    at com.yai.properti.tujuh.tujuh.tujuh.MainActivity.onCreate(MainActivity.java:817)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.app.Activity.performCreate(Activity.java:5163)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
07-25 16:04:27.287: E/AndroidRuntime(19823):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2061)
07-25 16:04:27.287: E/AndroidRuntime(19823):    ... 11 more

I've tried onDestroy() by replacing finish() call method, but NPE (Null Pointer Exception) still happened. As the first time intent to MainActivity, NPE not happended.

What i want is start MainActivity as the first time . How i could do that?

Many thanks.

Answer 1

i think there are little conceptual problem Actually FLAG_ACTIVITY_CLEAR_TOP flag is Use is check here: http://developer.android.com/reference/android/content/Intent.html#FLAG_ACTIVITY_CLEAR_TOP so in that case there are no need finish() method it is already Remove mainActivity class but according to document you have to add one more Flag FLAG_ACTIVITY_NEW_TASK to your intent.

So Replace

Intent i = new Intent(MainActivity.this, LoginActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
finish();

with

Intent i = new Intent(MainActivity.this, LoginActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);

thats it...

Answer 2

每当您需要调用finish()以完成anonymous inner class某些活动finish()如您在上面的代码中所做的那样）时，只需传递完整活动的名称（您要销毁的名称），例如MainActivity.this.finish() 。 （其中MainActivity是您要销毁的那个）

Answer 3

Create a static Activity object which activity finish on other activity and assign activity in this ie you can can add more activities

public class demoActivity extends AppCompatActivity {
    public static Activity self_intent;
    protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.demo_activity);
            selfintent=this;
    } 

   //Other functions--------------
} 

do same for other activities

on other

activityCloseBtn= (Button) view.findViewById(R.id.activity_close_btn);
activityCloseBtn.setOnClickListener(new View.OnClickListener() {      
       @Override
       public void onClick(View v) {
          demoActivity.selfintent.finish(); //for finish demoActivityactivity

          //for other activities Activity.selfintent.finish();
          finish();  //for finish current activity
      }
});