android - 在 Activity 之间切换 -> 无限循环

Question

我是 android 的新手，有一个“小”问题。

我正在开始扩展基类的主要 Activity 。基类开始我的“导航”类......在导航类中我有一个开关参数可供选择，应该创建哪个 Activity - 好吧，此时我有一个无限循环，我不知道为什么..

当我使用 fragment 时它工作正常但我想使用 Activity ......希望有人能帮助我:)

这是我的代码。

public class MainActivity extends Base {

@Override
protected void onCreate(Bundle savedInstanceState) {
    Log.v("boot", "MainActivity-onCreate");
    super.onCreate(savedInstanceState);

    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction()
            .replace(R.id.container, new MainFragment())
            .commit();
}

基地

public class Base extends ActionBarActivity implements
    NavigationDrawer.NavigationDrawerCallback {

public NavigationDrawer mNavigationDrawer;

@Override
protected void onCreate(Bundle savedInstanceState) {
    Log.v("boot", "Base-onCreate");
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // Set up the drawer
    mNavigationDrawer = (NavigationDrawer)
            getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);

    mNavigationDrawer.setUp((DrawerLayout)findViewById(R.id.drawer_layout),
            R.id.navigation_drawer);
}

导航

public class NavigationDrawer extends Fragment {

private ActionBarDrawerToggle mDrawerToggle;
private NavigationDrawerCallback mCallbacks;

private DrawerLayout mDrawerLayout;
private ListView mDrawerListView;
private View mFragmentContainer;

private boolean mUserLearnedNavigation;
private static final String PREF_USER_LEARNED_NAVI = "navigation_learned";
private static final String STATE_SELECTED_POSITION = "selected_position";

private int mCurrentSelectedPosition;
private boolean mFromSavedInstanceState;

@Override
public void onCreate(Bundle savedInstanceState) {
    Log.v("boot", "Nav - onCreate");
    super.onCreate(savedInstanceState);

    SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getActivity());
    mUserLearnedNavigation = sp.getBoolean(PREF_USER_LEARNED_NAVI, false);

    if (savedInstanceState != null) {
        mCurrentSelectedPosition = savedInstanceState.getInt(STATE_SELECTED_POSITION);
        mFromSavedInstanceState = true;
    }

    selectItem(mCurrentSelectedPosition);
} ... 
private void selectItem(int position) {
    Log.v("boot", "Nav - selectitem");
    mCurrentSelectedPosition = position;
    if (mDrawerListView != null) {
        mDrawerListView.setItemChecked(position, true);
    }

    if (mDrawerLayout != null) {
        mDrawerLayout.closeDrawer(mFragmentContainer);
    }

    if (mCallbacks != null) {
        mCallbacks.onNavigationDrawerItemClicked(position);
    }

    switch (position) {
        case 0:
            startActivity(new Intent(getActivity(), MainActivity.class));
            break;
        case 1:
            startActivity(new Intent(getActivity(), ExpensesActivity.class));
            break;
        default:
            startActivity(new Intent(getActivity(), MainActivity.class));
            break;
    }
}

Answer 1

每次您开始一项 Activity 时，您的菜单都会重新创建，因此 switch case 会被执行。您不应该在菜单的 onCreate 中调用 selectItem。如果您想保留用户导航，则必须在 MainActivity 中启动适当的 Activity 。

您可以在调用 startActivity 之前添加检查以查看 getActivity 是否是您要启动的 Activity 的实例，这样您就不会再次在无限循环中运行。