设置器中的意外 NullpointExpection [重复]

Question

我正在尝试做一个简单的操作：单击一个按钮并显示一个自定义 DialogFragment，但我得到一个 NullPointExpection，我不知道为什么。

mAlertDialog.java：

public class mAlertDialog extends DialogFragment {

    TextView title;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.dialog_invalid_time, container, false);
        title = (TextView)view.findViewById(R.id.titleText);
        return view;
    }

    public void setTheTitle(String title) {
        this.title.setText(title);
    }
}

显示 mAlertDialog：

mAlertDialog dialog = new mAlertDialog();
dialog.setTheTitle(getActivity().getString(R.string.invalidTimeTitle));
dialog.show(fm, "InvalidTime");

错误信息：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at m.inschool8.Objects.mAlertDialog.setTheTitle(mAlertDialog.java:20)
    at m.inschool8.bSubjects.Fragment_Subjects$55.onClick(Fragment_Subjects.java:2654)
    at android.view.View.performClick(View.java:4780)
    at android.view.View$PerformClick.run(View.java:19866)
    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:5254)
    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:903)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Answer 1

调用时title 仍然为空

mAlertDialog dialog = new mAlertDialog();
dialog.setTheTitle(getActivity().getString(R.string.invalidTimeTitle));

所以你可以做的是

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.dialog_invalid_time, container, false);
        title = (TextView)view.findViewById(R.id.titleText);
        setTheTitle(getActivity().getString(R.string.invalidTimeTitle));

        return view;
    }

// 调用它

mAlertDialog dialog = new mAlertDialog();
dialog.show(fm, "InvalidTime");

Answer 2

您的 title 为 null，直到显示 DialogFragment 导致 onCreateView 启动。因此更改顺序如下：

mAlertDialog dialog = new mAlertDialog();
dialog.show(fm, "InvalidTime");
dialog.setTheTitle(getActivity().getString(R.string.invalidTimeTitle));