Android NewBie - setAdapter ListView 面临的问题

Question

我是 Android 的新手，第一次尝试 Fragments。我使用了一个正在 fragment 中转换的 ListView Activity 。但不知何故，由 findViewById() 检索到的 ListView 元素给了我 null。谁能帮我解决这个问题？

这是 ListView Fragment 的代码，我在调用 setAdapter 方法后遇到错误。日志值显示 timeTrackerListView 为空。我不知道为什么。!! :(

 package ray.kaushik.nasaapp;

import android.app.Fragment;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;

public class TimeTracker extends Fragment{
    private Time_Tracker_Adapter timeTrackerAdapter;
    private String TAG = "TimeTracker";
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        timeTrackerAdapter = new Time_Tracker_Adapter();

    }

    public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle savedInstanceState){
            return inflater.inflate(R.layout.time__tracker_layout, container, false);
    }

    public void onActivityCreated(Bundle savedInstanceState){
        super.onActivityCreated(savedInstanceState);
        ListView timeTrackerListView = (ListView) getActivity().findViewById(R.id.time_tracker_List);
        Log.i(TAG, "timeTrackerListView-->" + timeTrackerListView);
        timeTrackerListView.setAdapter(timeTrackerAdapter);
    }
}

Answer 1

onCreate() 在 onCreateView() 之前被调用。 ListView 还没有膨胀，这就是为什么你找不到它的原因......

只需将当前的 onCreate() 代码移动到 onCreateView() 或 onActivityCreated() 即可。

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您应该能够在 onCreateView() 中设置您的 ListView，只需保存对膨胀 View 的引用即可:

public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle savedInstanceState){
    View view = inflater.inflate(R.layout.time__tracker_layout, container, false);
    ListView timeTrackerListView = (ListView) view.findViewById(R.id.time_tracker_List);
    timeTrackerAdapter = new Time_Tracker_Adapter();
    timeTrackerListView.setAdapter(timeTrackerAdapter);
    return view;
}

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图表来自 Developer's Guide :