Android：使用选项卡在不同片段之间切换

Posted 2023-04-15

【中文标题】Android：使用选项卡在不同片段之间切换

【英文标题】：Android: Switching between different fragments using tabs

【发布时间】：2015-02-23 09:02:42

【问题描述】：

我正在尝试实现工具栏选项卡，并让每个选项卡膨胀不同的片段，但是我遇到了错误：

java.lang.RuntimeException: Unable to start activity ComponentInfocom.danielkim.soundrecorder/com.danielkim.soundrecorder.MainActivity: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.os.Bundle.getInt(java.lang.String)' on a null object reference

这是我在MainActivity.java 中的适配器：

public class MyAdapter extends FragmentPagerAdapter 
    private String[] titles =  "Record", "Saved Recordings" ;
    public MyAdapter(FragmentManager fm) 
        super(fm);
    

    @Override
    public Fragment getItem(int position) 
        switch(position)
            case 0:
                return RecordFragment.newInstance(position);
            
            case 1:
                return FileViewerFragment.newInstance(position);
            
        
        return null;
    

    @Override
    public int getCount() 
        return titles.length;
    

    @Override
    public CharSequence getPageTitle(int position) 
        return titles[position];
    

和RecordFragment.java:

public static RecordFragment newInstance(int position) 
    RecordFragment f = new RecordFragment();
    Bundle b = new Bundle();
    b.putInt(ARG_POSITION, position);
    f.setArguments(b);
    return f;


public void onCreate(Bundle savedInstanceState) 
    super.onCreate(savedInstanceState);
    position = getArguments().getInt(ARG_POSITION);


    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) 
    View recordView = inflater.inflate(R.layout.fragment_record, container, false);

    mChronometer = (Chronometer) recordView.findViewById(R.id.chronometer);

    mRecordButton = (FloatingActionButton) recordView.findViewById(R.id.btnRecord);
    mRecordButton.setColorNormal(getResources().getColor(R.color.accent));
    mRecordButton.setOnClickListener(new View.OnClickListener() 
        @Override
        public void onClick(View v) 
            onRecord(mStartRecording);
            mStartRecording = !mStartRecording;
        
    );

    mPauseButton = (ImageButton) recordView.findViewById(R.id.btnPause);
    mPauseButton.setVisibility(View.GONE); //hide pause button before recording starts

    return recordView;

任何帮助将不胜感激，谢谢！

编辑：

这是完整的堆栈跟踪。我将适配器更改为使用 return RecordFragment.newInstance(position)，但仍然看到相同的错误。

12-25 16:16:42.845    2889-2889/com.danielkim.soundrecorder E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.danielkim.soundrecorder, PID: 2889
    java.lang.RuntimeException: Unable to start activity ComponentInfocom.danielkim.soundrecorder/com.danielkim.soundrecorder.MainActivity: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.os.Bundle.getInt(java.lang.String)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            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:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.os.Bundle.getInt(java.lang.String)' on a null object reference
            at com.danielkim.soundrecorder.fragments.RecordFragment.onCreate(RecordFragment.java:76)
            at android.support.v4.app.Fragment.performCreate(Fragment.java:1763)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:913)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
            at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:548)
            at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1220)
            at android.app.Activity.performStart(Activity.java:5949)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            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:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

【参考方案1】：

getArguments() 正在返回 null（因此，getArguments().getInt(ARG_POSITION) 的 NPE）因为您在创建 Fragment 后没有调用 setArguments()。

通常的模式是在 Fragment 类中有一个工厂方法来预加载参数。在这种情况下，它应该或多或少类似于：

public static RecordFragment newInstance(int position) 
    RecordFragment f = new RecordFragment();

    Bundle args = new Bundle();
    args.putInt(ARG_POSITION, position);
    f.setArguments(args);

    return f;

然后使用该方法创建Fragment，而不是直接调用构造函数。

【讨论】：

我也尝试过这种方法，但它似乎也抛出了同样的错误：public static RecordFragment newInstance(int position) RecordFragment f = new RecordFragment(); Bundle b = new Bundle(); b.putInt(ARG_POSITION, position); f.setArguments(b); return f; 在适配器中使用return RecordFragment.newInstance(position);（抱歉，格式很糟糕，不知道如何解决这个问题！ )

@DanielKim 可能还有其他错误。请发布完整的堆栈跟踪。

嗨，我已经编辑了完整的堆栈跟踪（使用return RecordFragment.newInstance(position)），谢谢！

@DanielKim 将position = getArguments().getInt(ARG_POSITION); 移动到onCreateView()。

【参考方案2】：

你可以使用

onCreateView() 方法在每个片段中并使用

ViewHolders

和

LayoutInflater你可以生成任何你想要的视图...