如何在父活动类（Android）中获取子活动视图？

Question

我实现了一个底部按钮栏（就像iPhone中的标签栏控制器）。为此，我创建了一个公共布局（button_bar.xml，5个图像按钮）并包含在其他活动xml文件中。并且为了管理点击操作，我创建了一个从Activity扩展的BaseActivity.java并执行点击操作。并且我扩展了其他需要使用此BaseActivity的按钮栏的活动，该工作正常。现在我想包含一个选定的状态到这些按钮，但是当我访问基本活动中的按钮时，它会给出一个空指针错误。我该如何解决这个问题。

button_bar.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:id="@+id/bottomButtonBar" 
style="@android:style/ButtonBar" 
... > 
<ImageButton 
    android:id="@+id/btnGuests" 
    android:onClick="showAllGuests" 
    android:src="@drawable/ic_guest_list" /> 

<ImageButton 
    android:id="@+id/btnAddGuest" 
    android:onClick="selectGuestType" 
    android:src="@drawable/ic_add_guest" /> 

<ImageButton 
    android:id="@+id/btnAddParty" 
    android:onClick="showAddParty" 
    android:src="@drawable/ic_add_party" /> 
    .... 
</LinearLayout> 

public class BaseActivity extends Activity { 
    // common to other activities. 
    public void showAddParty(View view) { 
    //showAddParty is one one of the buttons click method. 4 more buttons are there 
     Intent intent = new Intent(this, AddPartyActivity.class); 
     startActivity(intent); 

     // I can get "view.findViewById(R.id.btnAddParty)" here 
     // but I can't get "findViewById(R.id.btnAddGuest)" here. how this possible 
    } 
} 

public class AddPartyActivity extends BaseActivity{ 
    .... 
} 

在这里，我可以从参数查看相应的视图，并更改backgroundIbageSource。但是当它转到从Baseactivity继承的“AddPartyActivity”时，新图像会被旧图像替换。我如何在BaseActivity中实现所选功能？

Answer 1

您可以在BaseActivity中使用booloean来保存按钮的状态（单击或不按钮），并在AddPropertyActivity的onCreate()方法中检查这些变量的值。

public class BaseActivity extends Activity { 
    protected static boolean isButton1Clicked = false; 
    protected static boolean isButton2Clicked = false; 
    protected static boolean isButton3Clicked = false; 
    protected static boolean isButton4Clicked = false; 
    ..... 
    public void showAddParty(View view) { 
     isButton1Clicked = true; 
     //showAddParty is one one of the buttons click method. 4 more buttons are there 
     Intent intent = new Intent(this, AddPartyActivity.class); 
     startActivity(intent); 
    } 
} 


public class AddPartyActivity extends BaseActivity { 

    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_layout); 
     Button button1 = (Button)findViewById(R.id.button1); 
     if(isButton1Clicked) { 
      button1.setBackground(R.drawable.clicked); 
     } else { 
      button1.setBackground(R.drawable.not_clicked); 
     } 
     ...... 
     ...... 
     } 
} 

并记住所有布尔变量必须是static变量。 （每个对象都有自己的实例变量副本，但所有对象都会共享一个静态成员的副本）。

public class BaseActivity extends Activity { 

    protected static boolean isButton1Clicked = false; 
    protected static boolean isButton2Clicked = false; 
    protected static boolean isButton3Clicked = false; 
    protected static boolean isButton4Clicked = false; 
    protected Button button1; 
    protected Button button2; 
    protected Button button3; 
    protected Button button4; 

    protected void checkButtonsState() { 
     if (isButton1Clicked) { 
      button1.setBackgroundResource(R.drawable.image1); 
     } else { 
      button1.setBackgroundResource(R.drawable.image2); 
     } 
     .......... 
    } 

    public void showAddParty(View view) { 
     isButton1Clicked = true; 
     // showAddParty is one one of the buttons click method. 4 more 
     // buttons are there 
     Intent intent = new Intent(this, AddPartyActivity.class); 
     startActivity(intent); 
    } 
} 

public class AddPartyActivity extends BaseActivity { 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     button1 = (Button) findViewById(R.id.button); 
     button2 = (Button) findViewById(R.id.item1); 
      ..... 
     checkButtonsState(); 
    } 
} 

Answer 2

从因为您使用view.findViewById()，但对象是赶上click事件的看法变量对应（看在你的XML中，'android:onClick="showAddParty"')。

所以来你的错误，你的参数有查看实例直接指向btnAddParty按钮。 就是为什么你可以用findViewById访问btnAddParty ID，但不btnAddGuest ID。

您可以通过直接findViewById作为访问所有视图层次结构活动类的方法：

View btAddParty = findViewById(R.id.btnAddParty) 

View btAddGuest = view.findViewById(R.id.btnAddGuest) 

现在，你可以有一个完整的解决方案，以实现在BaseActivity一种特殊的方法（setMyInternalContent下面的示例中），并保持每个按钮的实例，之后，你就必须更新那里点击动作状态：

public class BaseActivity extends Activity { 
    protected Button mBtAddParty; 
    protected Button mBtAddGuest; 
    // ... 

    protected void setMyContentView(int resId) { 
     setContentView(resId); 
     mBtAddParty = (Button)findViewById(R.id.btnAddParty);    
     mBtAddParty = (Button)findViewById(R.id.btnAddGuest); 
     // ...    
    } 

    public void showAddParty(View view) { 
     mBtAddParty.setClickable(true); 
     mBtAddGuest.setClickable(false); 
     // ... 

     //showAddParty is one one of the buttons click method. 4 more buttons are there 
     Intent intent = new Intent(this, AddPartyActivity.class); 
     startActivity(intent); 
    } 
} 


public class AddPartyActivity extends BaseActivity { 

    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setMyContentView(R.layout.activity_layout); 

     // Do not forget to set initial button state:    
     mBtAddParty.setClickable(true); 
     mBtAddGuest.setClickable(false); 
     // ... 
    } 
}