訪問超類的視圖

Question

我想集中處理導航抽屜的代碼到所有活動擴展的超類中。超類本身擴展了Activity，但我似乎無法弄清楚如何訪問子類的視圖（findviewbyid返回null）。

如何從CommonCode訪問在CheckinActivity中膨脹的視圖？

超類的OnCreate：

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

子類

public class CheckInActivity extends CommonCode { 

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

    setContentView(R.layout.activity_main); 
} 

Answer 1

我要做的就是爲每個子活動單獨個XML，但有你的導航抽屜的所有XML IDS是相同的。

接下來，當您啓動擴展活動的任何子類時，請將捆綁的contextView id - R.layout.MY_SUB_ACTIVITY傳遞到捆綁包中，並實際爲您的超類中的每個子活動設置內容視圖。

之後，您可以使用findViewByID來查找抽屜，在超類中設置它們，然後從它自己的類中處理子類的視圖。

你的意見很可能返回null，因爲你之前，你的子類的運行你的父類的onCreate - 因此的setContentView沒有被調用，但（這樣findViewByID將無法正常工作）

編輯：

而且，您不必將所有導航抽屜ID命名爲相同 - 我只是覺得使用<include>標記更容易，可以最大限度地減少xml文件中的冗餘。

例如：

子類 -

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); 
     ..... 

    } 

父類：

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(); 
     } 
    }