java从超类访问视图

Question

我试图将处理导航抽屉的代码集中到一个所有活动都扩展的超类中。超级类本身扩展了活动，但我似乎不知道如何访问子类的视图（findviewbyid返回null）

如何从CommonCode访问CheckinActivity中膨胀的视图

超类oncreate：

public class CommonCode extends Activity{
....
    @Override
public void onCreate(Bundle b){
super.onCreate(b);
 context=getBaseContext();

子类

public class CheckInActivity extends CommonCode {

@Override
public void onCreate(Bundle b) {
    super.onCreate(b);

    setContentView(R.layout.activity_main);
}

Answer 1

我要做的是为每个子活动提供单独的xml，但导航抽屉的所有xml ID都是相同的

接下来，当您启动扩展活动的任何子类时，传递一个带有contextView id-R.layout的包。MY_SUB_活动-在一个捆绑包中，并实际设置超级类中每个子活动的内容视图

之后，您可以使用findViewByID查找抽屉，在超类中设置它们，然后从自己的类中处理子类的视图

您的视图可能会返回null，因为您在运行子类的onCreate之前运行了超类的onCreate，因此尚未调用setContentView（因此findViewByID将不起作用）

编辑：

此外，您不必为所有导航抽屉ID命名相同的名称，我只是认为使用<include>标记更容易，以最小化xml文件中的冗余

例如：

亚类-

public class InviteActivity extends MainActivity {

public static void openActivity(Activity from_activity) {
    Intent intent = new Intent(from_activity, InviteActivity.class);

    Bundle bundle = new Bundle();
    bundle.putInt(MainActivity.KEY_LAYOUT_ID, R.layout.invite_activity);
    bundle.putBoolean(MainActivity.KEY_HAS_LEFT_DRAWER, true);
    bundle.putBoolean(MainActivity.KEY_HAS_RIGHT_DRAWER, false);

    intent.putExtra(MainActivity.KEY_MAIN_BUNDLE, bundle);
    from_activity.startActivity(intent);
}

@Override
protected void onCreate(Bundle savedInstanceState){
      super.onCreate(savedInstanceState);
      .....

    }

超类：

public abstract class MainActivity extends Activity {

    /*
     * Bundle keys specifying if the new activity inheriting from MainActivity
     * has a left and/or right navigation drawer.
     */
    public static final String KEY_MAIN_BUNDLE = "com.smashingboxes.bevii.MAIN_BUNDLE_KEY";
    public static final String KEY_HAS_RIGHT_DRAWER = "com.smashingboxes.bevii.HAS_RIGHT_DRAWER";
    public static final String KEY_HAS_LEFT_DRAWER = "com.smashingboxes.bevii.HAS_LEFT_DRAWER";
    public static final String KEY_LAYOUT_ID = "com.smashingboxes.bevii.LAYOUT_ID_KEY";
    public static final String KEY_SECTION_TITLE = "comm.smashingboxes.bevii.SECTION_TITLE";

    /*
     * Boolean indicators for each activity specifying their active navigation
     * drawers.
     */
    private boolean hasRightDrawer;
    private boolean hasLeftDrawer;

    /* The current activity's layout id for setContentView */
    private String sectionTitle;
    private int contentID;

    /* UI Elements */
    private DrawerLayout mDrawerLayout;
    private ActionBarDrawerToggle mDrawerToggle;

    /* Reference to the ActionBar title to toggle text on drawer changes. */
    protected CustomTextView mTitle;

    private ListView mDrawerListLeft;
    private LeftNavigationAdapter leftAdapter;
    private ListView mDrawerListRight;
    private LeftMessagesAdapter rightAdapter;

    /**
     * Handles the navigation drawer set up for each class inheriting from main
     * activity. A bundle must be specified indicating the number of navigation
     * drawers present in the activity's UI.
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (!getIntent().hasExtra(KEY_MAIN_BUNDLE))
            throw new IllegalArgumentException(
                    "Cannot access a subclass of MainActivity without including a main bundle.");

        Bundle mainBundle = getIntent().getBundleExtra(KEY_MAIN_BUNDLE);
        hasRightDrawer = mainBundle.getBoolean(KEY_HAS_RIGHT_DRAWER);
        hasLeftDrawer = mainBundle.getBoolean(KEY_HAS_LEFT_DRAWER);
        contentID = mainBundle.getInt(KEY_LAYOUT_ID);
        sectionTitle = mainBundle.getString(KEY_SECTION_TITLE);

        setContentView(contentID);

        if (hasRightDrawer && hasLeftDrawer) {
            handleLeftNavigationDrawer();
            handleRightNavigationDrawer();
        } else if (hasLeftDrawer) {
            handleLeftNavigationDrawer();
        } 
    }