使用RecyclerView的Android语音识别

Question

我正在使用该项目https://github.com/googlesamples/android-RecyclerView作为参考来了解RecyclerView，并在这里实现MLProgrammer-Cim的答案来处理onClick事件。

在我的CustomAdapter活动中，我试图启动一个方法speakNow(); 在另一个活动MainActivity

public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.ViewHolder> {
private static final String TAG = "CustomAdapter";
...

public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
    ...
    public MyViewHolderClicks mListener;
    private Context context;
    MainActivity ma = new MainActivity();

//        FragmentTransaction ft =     ((FragmentActivity)context).getSupportFragmentManager().beginTransaction();
//        SampleActivityBase fragment = (SampleActivityBase)ft.findFragmentByTag("SampleActivityBase");


    public ViewHolder(View myv, MyViewHolderClicks listener) {

        super(myv);
        mListener = listener;
        ....
        imageIcon.setOnClickListener(this);
        myv.setOnClickListener(this);
        this.context =context;


    }
    @Override
    public void onClick(View v) {
       int position = getLayoutPosition();
        if (v instanceof Button){
            mListener.onTomato((Button) v, getLayoutPosition());
            switch (v.getId()) {

               case R.id.button_for_cardview:
                   ma.speakNow();
 .....
 }
}

我的MainActivity

public class MainActivity extends SampleActivityBase {
....
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
     ....
    //Intent intent = new Intent(getApplicationContext(),     CustomAdapter.class);
    //startActivityForResult(new Intent(this, CustomAdapter.class), checka);
    if (savedInstanceState == null) {
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        RecyclerViewFragment fragment = new RecyclerViewFragment();
        transaction.replace(R.id.sample_content_fragment, fragment);
        transaction.commit();
    }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

  if (requestCode == checka && resultCode == RESULT_OK){
        ArrayList<String> results = data.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS);
        lv.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, results));

       .....
        }

    }
    super.onActivityResult(requestCode, resultCode, data);


}

protected void speakNow() {
    Intent a = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
    a.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL, RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
    a.putExtra(RecognizerIntent.EXTRA_MAX_RESULTS, 6);
    a.putExtra(RecognizerIntent.EXTRA_PROMPT, GlobalVariables.getInstance().getRightAnswer1());
    startActivityForResult(a, checka);
}
....

}

这会在MainActivity.speakNow(MainActivity.java:478)返回一个NullPointerException，它是startActivityForResult(a, checka); 和Adapter $ ViewHolder.onClick（CustomAdapter.java:287），它是ma.speakNow();

我已经阅读了各种“其他活动返回NPE的调用方法”，问题和答案，但不太确定这些方法如何适用于我的案例，因为MainActivity扩展了SampleActivityBase ， SampleActivityBase是扩展FragmentActivity的公共抽象类。

我需要在哪里/如何初始化MainActivity ma = new MainActivity（）; 所以它不为空吗？ 谢谢

Answer 1

在startActivityForResult中引发该异常，这是因为MainActivity ma = new MainActivity();创建的Activity MainActivity ma = new MainActivity(); 与系统创建的Activity不同，您创建的Activity中没有任何内容，请读取Activity的源代码以执行startActivityForResult ，这取决于某些成员变量。因此，您会得到nullpoint异常。 您可以在适配器中添加设置器，将Activity的引用传递给适配器

public void setActivity(Activity aty) {
    this.aty = aty;
}