Question

在阅读了一些相关帖子后，我已经知道在尝试通过id将一个元素发现到Activity-View-Hierarchy之前，我必须显式调用setContenView。我创建了一个带有膨胀视图的活动，一切正常。问题是当我尝试使用下一个xml和代码设置此活动的另一个视图时：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="0dp"
android:paddingRight="0dp"
android:paddingTop="0dp"
android:paddingBottom="0dp"
android:background="#B12A6D"
tools:context=".MainActivity"
android:orientation="vertical"
>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="top"
    android:background="@drawable/bg_purple_500"
    android:layout_margin="0dp"
    >

<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/GridLayout1"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_weight="50"
        android:columnCount="4"
        android:rowCount="4"
        android:orientation="horizontal"
        tools:context=".GridXMLActivity"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="10dp"
        >

         <ImageView
            android:id="@+id/my_bnt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/icon_new_game"
            android:contentDescription="@string/text"
            android:layout_marginTop="10dp"
            android:layout_marginLeft="20dp"
            android:layout_marginRight="20dp"
            android:layout_marginBottom="10dp"
            />
</GridLayout>

</LinearLayout>

</RelativeLayout>

代码：

public class MainActivity extends ActionBarActivity {

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

    setContentView(R.layout.activity_main);

}


....

protected void method_triggered_from_UI_thread() {

  // Inflate other layout...
  View view = View.inflate(this, R.layout.my_layout, null) ;
  setContentView(view);
  ImageView btn = (ImageView) findViewById(R.id.my_bnt);
  // btn is null...

}

我尝试过其他轻微变化：

View mainView = findViewById(android.R.id.content);
LayoutInflater inflater = LayoutInflater.from(this);
View view = inflater.inflate(R.layout.my_layout, (ViewGroup) mainView, false)  ;
setContentView(view);
ImageView btn = (ImageView) view.findViewById(R.id.my_bnt);

我总是得到btn == null。我做错了什么？

THX

Answer 1

您可以尝试使用LayoutInflater。

View inflatedView = LayoutoutInflater.from(context).inflate(R.layout, null);
setContentView(inflatedView);

快乐编码

Answer 2

你确定btn和bnt是一样的吗？

我建议使用片段Google dev Fragments

但是，如果您想这样做，请提供您的外部＆＃39; main_activity.xml中的布局是一个特定的id，比如rootView。然后打电话给：

protected void methodTriggeredFromUiThread(){
    LinearLayout rootView = findViewById(R.id.rootView);
    View view = View.inflate(this, R.layout.my_layout, null) ;
    rootView.removeAllViews();
    rootView.addView(view);
    view.findViewById(R.id.my_bnt); 
}

要使用片段，请为您的活动可能具有的每种类型的视图创建一个实现Fragment的类。你的main_activity只会持有一个FrameLayout（除了持久标题，标签，等等）。由于按钮是一个视图，它位于主活动内部的片段内，只要片段被加载，主活动中任何地方调用findViewById（R.id.btn）都会产生按钮。

在activity_main.xml中的某个地方：

 <FrameLayout
        android:id="@+id/fragmentHolder"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
  </FrameLayout>

<强> MainActivity.java

public class MainActivity extends Activity {
    private FragmentManager mFragmentManager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        loadFragment(new DemoFragment());
    }
    protected void loadFragment(Fragment fragmentToLoad) {
        FragmentTransaction fragmentTransaction = mFragmentManager
            .beginTransaction();
        fragmentTransaction.replace(R.id.fragmentHolder, fragmentToLoad);
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }
}

<强> DemoFragment.java

public class DemoFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.my_layout,
                container, false);
    }
}

Answer 3

您必须等待更换结束。试试这个：

View view = View.inflate(this, R.layout.my_layout, null);
view.getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {          
     @Override          
     public void onGlobalLayout() {              
        // continue the initialization from here:
        btn = (ImageView) view.findViewById(R.id.my_bnt);
        //...

        view.getViewTreeObserver().removeGlobalOnLayoutListener(this);        
     }      
}); 
setContentView(view);

Answer 4

你可以试试这个，在 R.layout.activity_main中添加一些ViewGroup （FrameLayout），然后在method_triggered_from_UI_thread（）中添加膨胀的视图到该容器：

protected void method_triggered_from_UI_thread() {

// Inflate other layout...
  View view = View.inflate(this, R.layout.my_layout, null);

// add new view to the container view in activity layout
 (ViewGroup) findViewById(R.id.container).addView(view);

ImageView btn = (ImageView) findViewById(R.id.my_bnt);

}

Answer 5

抱歉，我没有意识到id存在my_bnt，但仅存在于一个现有布局中（不在layout-land或layout-xlarge中）。谢谢你的帮助

Answer 6

You can't assign a view,and do findviewbyid to an activity outside oncreate, an it just won't work. 
you need to rearrange your code in 
//declare image as global variable
ImageView btn;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
   Bundle extraArgs = getIntent().getExtras();
String layoutname=extraArgs.get("LayoutName");
if(layoutname="main")
    setContentView(R.layout.activity_main);
else 

  setContentView(R.layout.my_layout);
  btn = (ImageView) findViewById(R.id.my_bnt);

}



protected void method_triggered_from_UI_thread()
{
//Call the main activity again with bundle giving view 
Intent intent = new Intent();
intent.setClass(this, MainActivity.class);
intent.putExtra("LayoutName", "UR_LAYOUT_NAME");
startActivity(intent);/// or use startactivityforresult,

//access btn here
}

setContentView和findViewById

6 个答案: