发送回调后Android View为NULL答案

【问题标题】：Android View is NULL after sending callback发送回调后Android View为NULL
【发布时间】：2015-01-17 22:33:32
【问题描述】：

在我对用户进行身份验证后（使用 volley 库），我的 ServerConnection 类将带有用户名称的回调发送到我的 Fragment。我想在TextView 中显示用户名，但应用程序总是崩溃。

public class DrawerFragment extends Fragment implements ServerConnection.AuthenticationSuccessful {


TextView vDrawerName;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.drawer_default, container, false);
    vDrawerName = (TextView) view.findViewById(R.id.drawerName);
    vDrawerName.setText("Test"); // works
    ListView drawerList = (ListView) view.findViewById(R.id.drawerList);
    drawerList.setAdapter(new ArrayAdapter<>(this.getActivity(), android.R.layout.simple_list_item_1,
            new String[]{"Hallo", "test"}));
    return view;
}



@Override
public void onSuccess(String firstName, int id) {
        vDrawerName.setText(firstName); // view is null
}

}

ServerConnection.class

private AuthenticationSuccessful successful;

public ServerConnection(FragmentActivity activity, SharedPreferences sharedPreferences) {
    this.activity = activity;
    this.sharedPreferences = sharedPreferences;
    queue = Volley.newRequestQueue(activity);
    successful = new DrawerFragment();
}

public void authenticate(){
    //...
    successful.onSuccess("Name", 1);
}

public interface AuthenticationSuccessful {
    public void onSuccess(String firstName, int id);
}

在主活动中

ServerConnection connection = new ServerConnection(this,
                getSharedPreferences(ServerConnection.LOGIN_PREFERENCE, 0));
connection.authenticate();

日志猫

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at com.polat.mete.worknote.fragments.DrawerFragment.onSuccess(DrawerFragment.java:40)
        at com.polat.mete.worknote.ServerConnection$3.onResponse(ServerConnection.java:124)
        at com.polat.mete.worknote.ServerConnection$3.onResponse(ServerConnection.java:116)
        at com.android.volley.toolbox.JsonRequest.deliverResponse(JsonRequest.java:65)
        at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5223)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)

【问题讨论】：

你试过把TextView vDrawerName;改成final TextView vDrawerName;吗？
在服务器连接中，您创建了一个新片段 instance。在尝试调用onSuccess 之前，您是否真的在事务中提交了它？片段不依赖于连接，所以在外部和之前提交它。
@Leigh 如果您的实例是本地对象，则无法在全局范围内将对象设置为最终对象。

标签： android android-fragments android-asynctask

【解决方案1】：

试试这样的：

public class DrawerFragment extends Fragment implements ServerConnection.AuthenticationSuccessful {

TextView vDrawerName;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.drawer_default, container, false);
    vDrawerName = (TextView) view.findViewById(R.id.drawerName);
    vDrawerName.setText("Test"); // works
    ListView drawerList = (ListView) view.findViewById(R.id.drawerList);
    drawerList.setAdapter(new ArrayAdapter<>(this.getActivity(), android.R.layout.simple_list_item_1,
            new String[]{"Hallo", "test"}));
    return view;
}



@Override
public void onSuccess(String firstName, int id) {
        ((TextView) getActivity().findViewById(R.id.drawerName)).setText(firstName); // view is null
}

}

【讨论】：