java - 添加 TabListener 时出现 NullPointerException

Question

我在 LogCat 中收到此错误消息:

06-25 15:17:34.495: E/AndroidRuntime(5891): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.MainActivity}: java.lang.NullPointerException 06-25 16:07:43.589: E/AndroidRuntime(6587): Caused by: java.lang.NullPointerException 06-25 16:07:43.589: E/AndroidRuntime(6587): at com.example.MyTabsListener.onTabSelected(MyTabListener.java:28)

这是我的主要 Activity :

package com.example;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;

import com.actionbarsherlock.app.ActionBar;
import com.actionbarsherlock.app.SherlockActivity;

public class MainActivity extends SherlockActivity {    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ActionBar actionbar = getSupportActionBar();
        actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        ActionBar.Tab tab1 = actionbar.newTab().setText("Fragment A");
        SherlockFragment fragment1 = new AFragment();

        tab1.setTabListener(new MyTabsListener(fragment1, this
            .getApplicationContext()));
        actionbar.addTab(tab1);
    }

}

还有我的简单 TabListener:

package com.example;    

import android.content.Context;
import android.support.v4.app.FragmentTransaction;
import android.widget.Toast;  

import com.actionbarsherlock.app.ActionBar;
import com.actionbarsherlock.app.ActionBar.Tab;
import com.actionbarsherlock.app.SherlockFragment;

class MyTabsListener implements ActionBar.TabListener {
    public SherlockFragment fragment;
    private final Context appContext;

    public MyTabsListener(SherlockFragment fragment, Context ctx) {
        this.fragment = fragment;
        this.appContext = ctx;
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        Toast.makeText(this.appContext, "Reselected!", Toast.LENGTH_LONG)
                .show();
    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        ft.replace(R.id.fragment_container, fragment);
    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        ft.remove(fragment);
    }
}

最后是我的类(class) fragment A:

package com.example;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.actionbarsherlock.app.SherlockFragment;

public class AFragment extends SherlockFragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.weekdays, container, false);
    }

}

所以这个函数导致了 TabListener 中的错误:

@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
  ft.replace(R.id.fragment_container, fragment);
}

Answer 1

我刚刚遇到了和你一样的问题，我想我已经解决了。

基本上，您的 MainActivity 应该扩展 SherlockFragmentActivity 而不是 SherlockActivity。