Question

我有一个充满我的RecyclerView的适配器。由于onClick，当我单击RecyclerView的Item时，我存储了与查询匹配的数据库数据并启动了新的Activity。例如，我想用来自“名称”列的数据填充一个Activity的TextView。但是，当我单击RecyclerView的Item时，应用程序崩溃。我怎么解决这个问题？（如果需要，我可以提供更多代码或信息。）

MyAdapter.java代码：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> implements View.OnClickListener {
private ArrayList<MyObject> mItems = new ArrayList<>();
public String nametext;
DatabaseHelper myDB;
Main3Activity my3;
int idactivity;
String nameactivity;
int yearactivity;
int monthactivity;
int dayactivity;**




@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false);
    MyViewHolder vh=new MyViewHolder(view);
    view.setOnClickListener(this);

    return vh;
}

@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
    holder.bindData(getItem(position));
}

@Override
public int getItemCount() {
    return mItems.size();
}

public void updateData(ArrayList<MyObject> items) {
    mItems = new ArrayList<>(items);
    notifyDataSetChanged();
}

private MyObject getItem(int position) {
    if (position >= 0 && position < mItems.size())
        return mItems.get(position);

    return null;
}

@Override
public void onClick(View v) {
    idactivity = 0;
    nameactivity = null;
    yearactivity = 0;
    monthactivity = 0;
    dayactivity = 0;

    myDB = new DatabaseHelper(v.getContext());
    my3 = new Main3Activity();
    TextView clickedName=(TextView)v.findViewById(R.id.title);
     nametext = clickedName.getText().toString();
    Toast.makeText(v.getContext(),nametext,Toast.LENGTH_LONG).show();
    Cursor c = myDB.showDataonSelect(nametext);



    if(c.moveToFirst()) {

        idactivity = c.getInt(0) ;
        nameactivity = c.getString(1) ;
        yearactivity = c.getInt(2) ;
        monthactivity = c.getInt(3) ;
        dayactivity = c.getInt(4);

    }
    TextView txt1 = my3.getTxt1();
    txt1.setText(nameactivity);


    Intent myIntent = new Intent(v.getContext(), Main3Activity.class);

    v.getContext().startActivity(myIntent);


}



class MyViewHolder extends RecyclerView.ViewHolder {
    TextView title;
    TextView subTitle;

    MyViewHolder(View itemView) {
        super(itemView);
        title = itemView.findViewById(R.id.title);
        subTitle = itemView.findViewById(R.id.sub_title);
    }

    void bindData(MyObject myObject) {
        if (myObject == null)
            return;

        title.setText(myObject.title);
        subTitle.setText(myObject.subTitle);
    }
} }

Main3Activity.java代码：

public class Main3Activity extends AppCompatActivity{


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main3);

}
public TextView getTxt1(){
    TextView txt1 = findViewById(R.id.textView3);
    return txt1;
}}

logcat带有崩溃时出现的异常消息：

2019-06-06 18:12:27.721 15509-15509/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 15509
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.support.v7.app.AppCompatDelegateImpl.<init>(AppCompatDelegateImpl.java:249)
    at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:182)
    at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:520)
    at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:191)
    at com.example.myapplication.Main3Activity.getTxt1(Main3Activity.java:18)
    at com.example.myapplication.MyAdapter.onClick(MyAdapter.java:90)
    at android.view.View.performClick(View.java:6597)
    at android.view.View.performClickInternal(View.java:6574)
    at android.view.View.access$3100(View.java:778)
    at android.view.View$PerformClick.run(View.java:25885)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

我想从MyAdapter的onClick方法填充Activity的TextView。

Answer 1

似乎您想在用户使用项目标题单击某个项目时打开Main3Activity。这样做的方法是向活动传递额外的东西（也称为片段参数）

首先，您应该在MyViewHolder中实现View.OnClickListener：

class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

还将其从MyAdapter中删除：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

然后从MyViewHolder内的MyAdapter中移动onClick方法

同样在onClick方法中，不要使用Main3Activity构造函数。只需使用Intent并在标题上添加额外的内容即可。

@Override
public void onClick(View v) {
    Intent myIntent = new Intent(v.getContext(), Main3Activity.class);
    myIntent.putExtra("TITLE_EXTRA", title.getText().toString())
    v.getContext().startActivity(myIntent);
}

onClick方法中的其他任何内容都将其移至Main3Activity的onCreate或任何其他方法中。

要在Main3Activity中获取TITLE_EXTRA，请将其添加到您的onCreate方法中：

private String title;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.your_activity);
    ...
    if(getIntent() != null) {
        title = getIntent().getStringExtra("TITLE_EXTRA")
    }
    ...
}

Answer 2

从onClick中删除TextView TextView clickedName=(TextView)v.findViewById(R.id.title);的初始化，并在Holder类中对其进行初始化。

从Adapter类填充Activity的TextView的问题

2 个答案: