我正在尝试从数据库中提取后在NavigationView中设置名称和电子邮件。
以下是我在NavigationView方法中引用onCreate()的方法：
navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
但是，我仍然收到此错误：Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.support.design.widget.NavigationView.getHeaderView(int)' on a null object reference at com.abc.xyz.MainActivity.fetchDataFromProviderProvided(MainActivity.java:689)
这是fetchDataFromProviderProvided()方法：
public void fetchDataFromProviderProvided() {
if (authData != null) {
swipeRefreshLayout.setRefreshing(false);
if (authData.getProvider().equals("google")) {
fetchDataFromGoogle();
} else if (authData.getProvider().equals("facebook")) {
onFacebookAccessTokenChange(AccessToken.getCurrentAccessToken());
} else {
// DO SOMETHING TO FETCH USER'S NAME
String Uid = authData.getUid();
Log.d("Uid:", Uid);
Firebase userNameRef = mFirebaseRef.child(Uid + "/userName");
Log.d("userName", String.valueOf(userNameRef));
emailImage = (String) authData.getProviderData().get("profileImageURL");
// error on the line below
View imageView = navigationView.getHeaderView(0);
//
userImage = (ImageView) imageView.findViewById(R.id.userImage);
new emailProfilePicAsync().execute(authData.getUid());
View nameView = navigationView.getHeaderView(0);
userName = (TextView) nameView.findViewById(R.id.userName);
userNameRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
userName.setText(String.valueOf(dataSnapshot.getValue()));
}
@Override
public void onCancelled(FirebaseError firebaseError) {
}
});
emailName = userNameText;
emailEmail = (String) authData.getProviderData().get("email");
View emailView = navigationView.getHeaderView(0);
userEmail = (TextView) emailView.findViewById(R.id.userEmail);
userEmail.setText(emailEmail);
// System.out.println(post.getUserName());
// System.out.println(post.getUserEmail());
}
dataLoadingCompleteProgressDialog = ProgressDialog.show(MainActivity.this, "",
"Fetching user's info...", true);
if (dataLoadingCompleteProgressDialog.isShowing()) {
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
@Override
public void run() {
checkIfDataIsFetched();
dataLoadingCompleteProgressDialog.dismiss();
}
}, 5500);
}
} else {
}
}
这是activity_main.xml文件的代码：
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
android:id="@+id/drawer_layout"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">
<include
layout="@layout/app_bar_main"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
<android.support.design.widget.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer"/>
</android.support.v4.widget.DrawerLayout>
这是完整的堆栈跟踪：
FATAL EXCEPTION: main
Process: com.abc.xyz, PID: 19072
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.abc.xyz/com.abc.xyz.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.support.design.widget.NavigationView.getHeaderView(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.support.design.widget.NavigationView.getHeaderView(int)' on a null object reference
at com.abc.xyz.MainActivity.fetchDataFromProviderProvided(MainActivity.java:694)
at com.abc.xyz.MainActivity.onCreate(MainActivity.java:217)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
请告诉我这里有什么问题。
抱歉，问题格式不正确。我还是初学者。
答案 0 :(得分：1)
请确保在方法navigationView的调用完成之前初始化fetchDataFromProviderProvided()。
为了防止出现这样的错误，为了更好地维护代码，可以使用ButterKnife库。这很简单易用。
onCreate()方法调用Butterknife.bind()中并初始化任何View个对象执行以下操作：
@Bind(R.id.nav_view)
NavigationView navigationView;
希望这有帮助。
答案 1 :(得分：0)
添加以下行：
查看标题= navigationView.getHeaderView（0）;
navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
View header = navigationView.getHeaderView(0);