android.view.View.findViewById(int)' on a null object reference

Question

我在toolbar有一个spinner

<android.support.v7.widget.Toolbar
android:id="@+id/main_toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="@color/colorToolBar"
android:minHeight="?attr/actionBarSize"
app:titleTextColor="#fff"
app:theme="@style/ToolbarStyle">
<Spinner
android:id="@+id/Transaction_type"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_gravity="right">
</Spinner>
</android.support.v7.widget.Toolbar>

而这个，我的adapter和xml来源：

private class spinnerAdapter extends BaseAdapter {
@Override
public int getCount() {
return 3;
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
@SuppressLint("ResourceType")
@Override
public View getView(int position, View convertView, ViewGroup parent) {
convertView = getLayoutInflater().inflate(R.layout.custom_spinner_item, null);
TextView item = (TextView) convertView.findViewById(R.id.spinner_txt1);
item.setText(transactionType[position]);
return convertView;
}
}

和custom_spinner_item.xml

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/spinner_txt1"
android:layout_width="match_parent" android:layout_height="match_parent"
android:textColor="#000"
android:gravity="right"
android:textSize="16dp"
android:padding="10dp">

I 通过parent.getChildAt()更改所选微调器项目的颜色

TransactionTypeSpiner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
((TextView) parent.getChildAt(0)).setTextColor(Color.WHITE);
}

但是我收到此错误：

09-04 08:18:01.405 28605-28605/? E/Zygote: v2 09-04 08:18:01.405 28605-28605/? E/Zygote: accessInfo : 0 09-04 08:18:03.365 28605-28605/com.niyazdel.app.jeeb E/MotionRecognitionManager: mSContextService = null
motionService = null 09-04 08:19:04.925 28605-28605/? E/MotionRecognitionManager: mSContextService = null 09-04 08:19:04.925 28605-28605/? E/MotionRecognitionManager: motionService = null 09-04 08:19:05.065 28605-28605/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.niyazdel.app.jeeb, PID: 28605
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.niyazdel.app.jeeb.MainActivity$3.onItemSelected(MainActivity.java:144)
at android.widget.AdapterView.fireOnSelected(AdapterView.java:1166)
at android.widget.AdapterView.dispatchOnItemSelected(AdapterView.java:1155)
at android.widget.AdapterView.selectionChanged(AdapterView.java:1146)
at android.widget.AdapterView.checkSelectionChanged(AdapterView.java:1327)
at android.widget.AdapterView.handleDataChanged(AdapterView.java:1303)
at android.widget.AbsSpinner.onMeasure(AbsSpinner.java:181)
at android.widget.Spinner.onMeasure(Spinner.java:632)
at android.support.v7.widget.AppCompatSpinner.onMeasure(AppCompatSpinner.java:420)
at android.view.View.measure(View.java:20221)
at android.support.v7.widget.Toolbar.measureChildCollapseMargins(Toolbar.java:1547)
at android.support.v7.widget.Toolbar.onMeasure(Toolbar.java:1655)
at android.view.View.measure(View.java:20221)
at android.widget.RelativeLayout.measureChild(RelativeLayout.java:677)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:480)
at android.view.View.measure(View.java:20221)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6333)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:141)
at android.view.View.measure(View.java:20221)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6333)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
at android.view.View.measure(View.java:20221)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6333)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:20221)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6333)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
at android.view.View.measure(View.java:20221)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6333)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:3140)
at android.view.View.measure(View.java:20221)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2687)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1640)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1932)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1528)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7530)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
at android.view.Choreographer.doCallbacks(Choreographer.java:686)
at android.view.Choreographer.doFrame(Choreographer.java:622)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7325)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

如何解决这个问题？！ 谢谢。

Answer 1

在onItemSelected尝试从View中获取文本视图，如下所示：

public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
TextView tv = view.findViewById(R.id.spinner_txt1);
tv.setTextColor(Color.WHITE);
}

更新：

我认为这是来自你的convertView.您必须检查convertView是否为空，如果为空，则夸大您的视图。这应该在你的getView()内：

View view;
if (convertView == null) {
view = getLayoutInflater().inflate(R.layout.custom_spinner_item, null);
} else {
view = convertView
}
TextView item = (TextView) view.findViewById(R.id.spinner_txt1);
item.setText(transactionType[position]);

Answer 2

微调适配器代码有错误，如下所示：

@Override
public Object getItem(int position) {
return position; //here
}
@Override
public long getItemId(int position) {
return position;//and here
}

其他逻辑是正确的，只需修改上面的行即可。

Answer 3

您的custom_spinner_item.xml文件内容是直接文本视图。因此，您不会在"custom_spinner_item.xml"中找到spinner_txt1。

所以，你需要使用convertView = getLayoutInflater().inflate(R.layout.custom_spinner_item, null);并将您的隐蔽视图键入到文本视图，以便您可以设置文本。

TextView item = (TextView) convertView;
item.setText(transactionType[position]);

并且您可以直接使用onItemSelected中的视图作为文本视图：

public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
((TextView) parent).setTextColor(Color.WHITE);
}

所有这些都需要执行，因为您将 TextView 作为custom_spinner_item.xml中的父视图

或者，只需将任何视图组添加到您的custom_spinner_item.xml，然后您就可以使用您的onItemSelected代码。