Task#performClearTop

    binding.next2.setOnClickListener {
            val intent = Intent()
            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
            intent.setClass(this,DongGangAppListActivity::class.java)
            startActivity(intent)
        }

  public static final int FLAG_ACTIVITY_CLEAR_TOP = 0x04000000;

    ActivityRecord performClearTop(ActivityRecord newR, int launchFlags, int[] finishCount) {
        // The task should be preserved for putting new activity in case the last activity is
        // finished if it is normal launch mode and not single top ("clear-task-top").
        mReuseTask = true;
        mTaskSupervisor.beginDeferResume();
        final ActivityRecord result;
        try {
            result = clearTopActivities(newR, launchFlags, finishCount);
        } finally {
            mTaskSupervisor.endDeferResume();
            mReuseTask = false;
        }
        return result;
    }

    private ActivityRecord clearTopActivities(ActivityRecord newR, int launchFlags,
            int[] finishCount) {
        final ActivityRecord r = findActivityInHistory(newR.mActivityComponent, newR.mUserId);
        if (r == null) return null;

        final PooledPredicate f = PooledLambda.obtainPredicate(
                (ActivityRecord ar, ActivityRecord boundaryActivity) ->
                        finishActivityAbove(ar, boundaryActivity, finishCount),
                PooledLambda.__(ActivityRecord.class), r);
        forAllActivities(f);
        f.recycle();

        // Finally, if this is a normal launch mode (that is, not expecting onNewIntent()), then we
        // will finish the current instance of the activity so a new fresh one can be started.
        if (r.launchMode == ActivityInfo.LAUNCH_MULTIPLE
                && (launchFlags & Intent.FLAG_ACTIVITY_SINGLE_TOP) == 0
                && !ActivityStarter.isDocumentLaunchesIntoExisting(launchFlags)) {
            if (!r.finishing) {
                r.finishIfPossible("clear-task-top", false /* oomAdj */);
            }
        }

        return r;
    }

    private static boolean finishActivityAbove(ActivityRecord r, ActivityRecord boundaryActivity,
            @NonNull int[] finishCount) {
        // Stop operation once we reach the boundary activity.
        if (r == boundaryActivity) return true;

        if (!r.finishing && !r.isTaskOverlay()) {
            final ActivityOptions opts = r.getOptions();
            if (opts != null) {
                r.clearOptionsAnimation();
                // TODO: Why is this updating the boundary activity vs. the current activity???
                boundaryActivity.updateOptionsLocked(opts);
            }
            finishCount[0] += 1;
            r.finishIfPossible("clear-task-stack", false /* oomAdj */);
        }

        return false;
    }