目前我正致力于Android中Fragment和Activity之间的沟通。我想在这里实现的是在Fragment中的按钮上设置onClickListener。然而，NPE发生，我不知道为什么。堆栈流程中有许多类似的问题，但我没有找到适合我的问题。以下是我的代码和logcat。已经被困在这里一段时间，希望有人可以帮助我！
logcat的：
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity
> ComponentInfo{com.example.ivylin.corewar/com.example.ivylin.corewar.assistantWidgets.WarriorBattleSelfScreen}:
> android.view.InflateException: Binary XML file line #7: Error
> inflating class fragment
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.access$800(ActivityThread.java:144)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5221)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: Caused by: android.view.InflateException: Binary XML file line #7: Error
> inflating class fragment
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:763)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.example.ivylin.corewar.assistantWidgets.WarriorBattleSelfScreen.onCreate(WarriorBattleSelfScreen.java:36)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.Activity.performCreate(Activity.java:5933)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.access$800(ActivityThread.java:144)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5221)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
> android.widget.Button.setOnClickListener(android.view.View$OnClickListener)'
> on a null object reference
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.example.ivylin.corewar.assistantWidgets.WarriorBattleFragment.onCreateView(WarriorBattleFragment.java:46)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.Fragment.performCreateView(Fragment.java:2053)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:870)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1045)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.FragmentManagerImpl.addFragment(FragmentManager.java:1147)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2116)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.Activity.onCreateView(Activity.java:5282)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:34)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:79)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:733)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.example.ivylin.corewar.assistantWidgets.WarriorBattleSelfScreen.onCreate(WarriorBattleSelfScreen.java:36)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.Activity.performCreate(Activity.java:5933)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.access$800(ActivityThread.java:144)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5221)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
> 04-14 17:53:02.163 15136-15136/? E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
似乎logcat主要告诉按钮bOK为空。查看下面的详细代码。
我的片段：
public class WarriorBattleFragment extends Fragment implements View.OnClickListener {
private RecyclerView recyclerView;
private WarriorBattleAdapter adapter;
EditText nP1;
EditText nP2;
Button bStart;
static private int click;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstance) {
View layout = inflater.inflate(R.layout.activity_warrior_self_battle_recyclerview, container, false);
recyclerView = (RecyclerView) layout.findViewById(R.id.recycler_view);
LinearLayoutManager layoutManager;
bStart = (Button) recyclerView.findViewById(R.id.bOK);
nP1 = (EditText) recyclerView.findViewById(R.id.nP1);
nP2 = (EditText) recyclerView.findViewById(R.id.nP2);
bStart.setOnClickListener(this);
layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false);
recyclerView.setLayoutManager(layoutManager);
adapter = new WarriorBattleAdapter(getActivity());
recyclerView.setAdapter(adapter);
return layout;
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.bStart:
if (UserInformation.selectedBW[0].equals("") && UserInformation.selectedBW[1].equals("")) {
Toast.makeText(getActivity().getApplicationContext(), "Please Choose A Warrior", Toast.LENGTH_SHORT).show();
} else {
click++;
if (click == 1) {
nP1.setText(UserInformation.selectedBW[0]);
adapter.setAdded(1);
} else if (click == 2) {
bStart.setText("BATTLE!");
} else if (click == 3) {
Toast.makeText(getActivity().getApplicationContext(), "WARRIOR FILES UPLOADING", Toast.LENGTH_SHORT).show();
}
}
if (!UserInformation.selectedBW[0].equals("")) {
Intent intent = new Intent(getActivity().getApplicationContext(), DemoDisplay.class);
intent.putExtra("wName", UserInformation.selectedBW[0]);
intent.putExtra("MODE", UserInformation.selectedBW[0]);
startActivity(intent);
} else {
Toast.makeText(getActivity().getApplicationContext(), "Please select one warrior", Toast.LENGTH_SHORT).show();
}
break;
}
}
}
我的活动：
public class WarriorBattleSelfScreen extends AppCompatActivity implements View.OnClickListener {
Button bBack;
Intent intent;
static int click;
@Override
protected void onCreate(Bundle savedInstanceState) {
// set to full screen
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_warrior_battle_self_screen);
bBack = (Button) findViewById(R.id.bBack);
// THIS PART IS FOR TEST
UserInformation.empty = false;
WarriorCardEntity imp = new WarriorCardEntity();
imp.title = "Imp";
imp.image = R.drawable.w9;
UserInformation.dataContainer.put(0, imp);
WarriorCardEntity rave = new WarriorCardEntity();
rave.title = "Rave";
rave.image = R.drawable.w10;
UserInformation.dataContainer.put(1, rave);
WarriorCardEntity lin = new WarriorCardEntity();
lin.title = "lin";
lin.image = R.drawable.w20;
UserInformation.dataContainer.put(2, lin);
bBack.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.bBack:
finish();
break;
}
}
}
XML：
activity_warrior_self_battle_recyclerview
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
android:screenOrientation="landscape"
>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_centerInParent="true">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentBottom="true">
</android.support.v7.widget.RecyclerView>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="P1: "
android:textSize="20sp"
android:textColor="@color/white"
android:id="@+id/tP1"
/>
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/nP1"
android:layout_toRightOf="@+id/tP1"
android:hint="WARRIOR1"
android:textColor="@color/white"
android:textColorHint="@color/white"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="P2: "
android:layout_marginLeft="400dp"
android:textSize="20sp"
android:textColor="@color/white"
android:id="@+id/tP2"
/>
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/nP2"
android:layout_toRightOf="@+id/tP2"
android:layout_alignParentRight="true"
android:hint="WARRIOR2"
android:textColor="@color/white"
android:textColorHint="@color/white"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="OK"
android:background="@drawable/button"
android:textColor="@color/white"
android:id="@+id/bOK"
android:layout_marginRight="33dp"
android:layout_marginEnd="33dp"
android:layout_marginBottom="0dp"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
</RelativeLayout>
</RelativeLayout>
活动中的XML-- activity_warrior_battle_self_screen
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:screenOrientation="landscape"
android:background="@drawable/background_gene">
<fragment class="com.example.ivylin.corewar.assistantWidgets.WarriorBattleFragment"
android:id="@+id/b_self_fragment"
android:layout_width="match_parent"
android:layout_height="320dp"
android:layout_centerVertical="true"
android:layout_toRightOf="@+id/Add"
android:layout_toEndOf="@+id/Add"
android:layout_marginLeft="30dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Back"
android:background="@drawable/button"
android:textColor="@color/white"
android:id="@+id/bBack"
android:layout_marginLeft="33dp"
android:layout_marginStart="33dp"
android:layout_marginBottom="20dp"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
</RelativeLayout>
答案 0 :(得分：1)
您在RecyclerView上呼叫findViewById()。
您需要在根视图中调用它：
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstance) {
View layout = inflater.inflate(R.layout.activity_warrior_self_battle_recyclerview, container, false);
recyclerView = (RecyclerView) layout.findViewById(R.id.recycler_view);
LinearLayoutManager layoutManager;
//change to layout.findViewById():
bStart = (Button) layout.findViewById(R.id.bOK); //modified
nP1 = (EditText) layout.findViewById(R.id.nP1); //modified
nP2 = (EditText) layout.findViewById(R.id.nP2); //modified
bStart.setOnClickListener(this);
layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false);
recyclerView.setLayoutManager(layoutManager);
adapter = new WarriorBattleAdapter(getActivity());
recyclerView.setAdapter(adapter);
return layout;
}
答案 1 :(得分：0)
是的，您对recyclerView.findViewById(R.id.bOK);的调用返回null。这是因为ViewGroup recyclerView中没有ID为'bOK'的按钮，您正在尝试使用findViewById()找到按钮。
在您的布局中，您可以立即打开和关闭RecyclerView标签：
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentBottom="true">
</android.support.v7.widget.RecyclerView>
那可能只是偶然的。您应该关闭标签，直到按钮之后，如下所示 - 如果按钮应该在RecyclerView中：
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="OK"
android:background="@drawable/button"
android:textColor="@color/white"
android:id="@+id/bOK"
android:layout_marginRight="33dp"
android:layout_marginEnd="33dp"
android:layout_marginBottom="0dp"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
</android.support.v7.widget.RecyclerView>
答案 2 :(得分：0)
您应该根据@Micha和@Daniel
<强> BUT
日志描述了一个完全不同的问题 -
您已在android:screenOrientation="landscape"
RelativeLayout设置了属性activity_warrior_self_battle_recyclerview.xml
那是不正确的
android:screenOrientation不是RelativeLayout的有效Android属性。