findViewWithTag返回null

我試圖設置ViewPagers加載3 XML文件。我們稱之爲ViewPagerAdapter.java

在對象實例化，我試圖改變使用findViewWithTag()所有的文本框的字體。但是當EditText定義爲findViewWithTag()時，它返回null（使用system.out.println），這導致setTypeFace錯誤。

我的代碼有問題嗎？

Object Instantiate Code (ViewPagerAdapter.java) 

public Object instantiateItem(View collection, int position) { 

     LayoutInflater inflater = (LayoutInflater) collection.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     int resId = 0; 

     switch(position) { 
     case 0: 
      resId = R.layout.activity_login; 
      break; 
     case 1: 
      resId = R.layout.activity_register; 
      break; 
     case 2: 
      resId = R.layout.activity_vote; 
      break; 
     } 
     View view = inflater.inflate(resId, null); 
     EditText txtFields = (EditText) view.findViewWithTag("abeezee"); 
      txtFields.setTypeFace(Typeface.DEFAULT_BOLD); //This one cause the error (Line 39) 
     System.out.println(txtFields); 

     ((ViewPager) collection).addView(view, 0); 
     return view; 
    }

其中的XML（可activity_register.xml）：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/layRegister" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:background="@android:color/transparent" 
    android:orientation="vertical" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" > 

    <TextView 
     android:id="@+id/tvRegisterTitle" 
     style="@style/title" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_alignLeft="@+id/etNameReg" 
     android:layout_alignParentTop="true" 
     android:text="@string/register_text" 
     android:textAppearance="?android:attr/textAppearanceLarge" 
     /> 

    <EditText 
     android:id="@+id/etNameReg" 
     style="@style/textfield" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/spVoteMlm" 
     android:layout_centerHorizontal="true" 
     android:layout_marginTop="15dp" 
     android:ems="10" 
     android:hint="@string/name_hint" 
     android:inputType="textPersonName" 
     android:tag="abeezee" 
     > 

     <requestFocus /> 
    </EditText> 

    <EditText 
     android:id="@+id/etEmailReg" 
     style="@style/textfield" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/etNameReg" 
     android:layout_centerHorizontal="true" 
     android:layout_marginTop="15dp" 
     android:ems="10" 
     android:hint="@string/email_hint" 
     android:inputType="textEmailAddress" 
     android:tag="abeezee" 
     /> 

    <EditText 
     android:id="@+id/etPasswordReg" 
     style="@style/textfield" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_alignLeft="@+id/etEmailReg" 
     android:layout_below="@+id/etEmailReg" 
     android:layout_centerVertical="true" 
     android:layout_marginTop="15dp" 
     android:ems="10" 
     android:hint="@string/password_hint" 
     android:typeface="serif" 
     android:inputType="textPassword" 
     android:tag="abeezee" 
     /> 

    <Spinner 
     android:id="@+id/spVoteMlm" 
     style="@style/textfield" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_centerHorizontal="true" 
     android:layout_below="@+id/tvRegisterTitle" 
     android:layout_marginTop="30dp" 
     android:entries="@array/mlm_list" 
     android:tag="abeezee" 
     /> 

    <Button 
     android:id="@+id/btnRegister" 
     style="@style/buttonBlue" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/btnTerms" 
     android:layout_centerHorizontal="true" 
     android:layout_marginTop="15dp" 
     android:text="@string/register_text" /> 

    <Button 
     android:id="@+id/btnTerms" 
     style="@style/smallLink" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_below="@+id/etPasswordReg" 
     android:layout_centerHorizontal="true" 
     android:gravity="center" 
     android:onClick="showTermsPolicy" 
     android:text="@string/terms_policy" /> 

</RelativeLayout>

logcat的錯誤：

09-24 13:17:49.178: E/AndroidRuntime(16278): FATAL EXCEPTION: main 
09-24 13:17:49.178: E/AndroidRuntime(16278): java.lang.NullPointerException 
09-24 13:17:49.178: E/AndroidRuntime(16278): at com.sociyo.ViewPagerAdapter.instantiateItem(ViewPagerAdapter.java:39) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.support.v4.view.PagerAdapter.instantiateItem(PagerAdapter.java:110) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:832) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.support.v4.view.ViewPager.populate(ViewPager.java:982) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.support.v4.view.ViewPager.populate(ViewPager.java:914) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.View.measure(View.java:15392) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:622) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:404) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.View.measure(View.java:15392) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4924) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.widget.FrameLayout.onMeasure(FrameLayout.java:314) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.View.measure(View.java:15392) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4924) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1420) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.widget.LinearLayout.measureVertical(LinearLayout.java:697) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.widget.LinearLayout.onMeasure(LinearLayout.java:578) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.View.measure(View.java:15392) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4924) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.widget.FrameLayout.onMeasure(FrameLayout.java:314) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2154) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.View.measure(View.java:15392) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1865) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1286) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1011) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4244) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.Choreographer.doCallbacks(Choreographer.java:555) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.Choreographer.doFrame(Choreographer.java:525) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.os.Handler.handleCallback(Handler.java:615) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.os.Handler.dispatchMessage(Handler.java:92) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.os.Looper.loop(Looper.java:213) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at android.app.ActivityThread.main(ActivityThread.java:4793) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at java.lang.reflect.Method.invokeNative(Native Method) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at java.lang.reflect.Method.invoke(Method.java:511) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556) 
09-24 13:17:49.178: E/AndroidRuntime(16278): at dalvik.system.NativeStart.main(Native Method)

來源

2013-09-24 Yansen Tan

您也必須用EditText標識標籤。 DVM找不到具有上述標籤的任何元素，因此返回null。 – Amit

Like android：tag =「abeezee」 – Amit

使用「EditText」的ID，以便第38行看起來像：「EditText txtFields =（EditText）view.findViewById（R.id.etNameReg）;' – ozbek

您可以使用下面的getViewsByTag函數從父元素進行迭代，並得到所有它包含的「標記的」子元素。然後，您可以遍歷這些視圖，並使用switch語句和instanceof以不同方式處理Button，EditText或TextView元素。

public static ArrayList<View> getViewsByTag(ViewGroup root, String tag){ 
    ArrayList<View> views = new ArrayList<View>(); 
    final int childCount = root.getChildCount(); 
    for (int i = 0; i < childCount; i++) { 
     final View child = root.getChildAt(i); 
     if (child instanceof ViewGroup) { 
      views.addAll(getViewsByTag((ViewGroup) child, tag)); 
     } 

     final Object tagObj = child.getTag(); 
     if (tagObj != null && tagObj.equals(tag)) { 
      views.add(child); 
     } 

    } 
    return views; 
}

來源

2013-12-11 23:05:37 LocalPCGuy

findViewWithTag返回null

回答

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