`NotifyDatasetchanged`不起作用。在点击按钮后应用程序崩溃。

huangapple
未分类评论58阅读模式
英文:

NotifyDatasetchanged not working. AppCrashes after ButtonOnClick

问题

以下是翻译好的部分：

我一直在尝试创建一个按钮，当点击按钮时，可以将新值添加到我的ArrayList（countries）中，但实际上应用程序崩溃了，而不是添加我的项目（Card）。我还在使用Fragments。以下是我的代码。

这是我的Fragment页面类：

package com.example.barryblack;

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

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;

public class FragmentPage extends Fragment {

    private RecyclerView.Adapter mAdapter;
    private ArrayList<String> countries;
    Button btn;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        CreateExampleList();

        View view = inflater.inflate(R.layout.page_fragment, container, false);

        RecyclerView recyclerView = view.findViewById(R.id.listRecyclerView);

        btn = view.findViewById(R.id.button_insert);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                InsertItem();
            }
        });

        recyclerView.setHasFixedSize(true);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity());
        recyclerView.setLayoutManager(layoutManager);
        RecyclerView.Adapter adapter = new MyAdapter(countries);
        recyclerView.setAdapter(adapter);

        return view;
    }

    public void InsertItem() {
        countries.add("Smile");
        mAdapter.notifyDataSetChanged();
    }

    private void CreateExampleList() {
        countries = new ArrayList<>();
        countries.add("Eat");
        countries.add("Kill");
    }
}

这是我的自定义适配器类：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    private ArrayList<String> cards;

    public MyAdapter(ArrayList<String> countries) {
        this.cards = countries;
    }

    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.example_item, viewGroup, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(MyAdapter.ViewHolder viewHolder, int i) {
        viewHolder.tv_country.setText(cards.get(i));
    }

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

    public class ViewHolder extends RecyclerView.ViewHolder {
        private TextView tv_country;

        public ViewHolder(View view) {
            super(view);
            tv_country = (TextView) view.findViewById(R.id.tv_country);
        }
    }
}

这是您提供的Logcat日志：

java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView$Adapter.notifyDataSetChanged()' on a null object reference
at com.example.barryblack.FragmentPage.InsertItem(FragmentPage.java:60)
at com.example.barryblack.FragmentPage$1.onClick(FragmentPage.java:43)

英文:

I've been trying to create a button that adds a new Value to my Arraylist (contries) when clicked, but it instead of adding my item(Card) the app simply crashes. I am also using Fragments. Here's my code.

That one is my Class for my FragmentPage

package com.example.barryblack;

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

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import java.util.ArrayList;

public class FragmentPage extends Fragment {

private RecyclerView.Adapter mAdapter;
private ArrayList countries;
Button btn;






@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable 
Bundle savedInstanceState) {

    CreateExampleList();

    View view = inflater.inflate(R.layout.page_fragment, container, false);

    RecyclerView recyclerView = view.findViewById(R.id.listRecyclerView);

    btn = view.findViewById(R.id.button_insert);

    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            InsertItem();

        }
    });

    recyclerView.setHasFixedSize(true);
    RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity());
    recyclerView.setLayoutManager(layoutManager);
    RecyclerView.Adapter adapter = new MyAdapter(countries);
    recyclerView.setAdapter(adapter);


    return view;
}

public void InsertItem() {
    countries.add(&quot;Smile&quot;);
    mAdapter.notifyDataSetChanged();


}

private void CreateExampleList() {
    countries = new ArrayList&lt;String&gt;();
    countries.add(&quot;Eat&quot;);
    countries.add(&quot;Kill&quot;);

}





}

This is my CustomAdapter

public class MyAdapter extends RecyclerView.Adapter&lt;MyAdapter.ViewHolder&gt; {
private ArrayList&lt;String&gt; cards;

public MyAdapter(ArrayList&lt;String&gt; countries) {
    this.cards = countries;
}

@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
    View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.example_item, viewGroup, 
false);
    return new ViewHolder(view);
}

@Override
public void onBindViewHolder(MyAdapter.ViewHolder viewHolder, int i) {

    viewHolder.tv_country.setText(cards.get(i));
}

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

public class ViewHolder extends RecyclerView.ViewHolder{
    private TextView tv_country;
    private Button tv_button;
    public ViewHolder(View view) {
        super(view);

        tv_country = (TextView)view.findViewById(R.id.tv_country);

    }
}

}public class MyAdapter extends RecyclerView.Adapter&lt;MyAdapter.ViewHolder&gt; {
private ArrayList&lt;String&gt; cards;

public MyAdapter(ArrayList&lt;String&gt; countries) {
    this.cards = countries;
}

@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
    View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.example_item, viewGroup, 
false);
    return new ViewHolder(view);
}

@Override
public void onBindViewHolder(MyAdapter.ViewHolder viewHolder, int i) {

    viewHolder.tv_country.setText(cards.get(i));
}

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

public class ViewHolder extends RecyclerView.ViewHolder{
    private TextView tv_country;
    private Button tv_button;
    public ViewHolder(View view) {
        super(view);

        tv_country = (TextView)view.findViewById(R.id.tv_country);

    }
}

}

And my LogcatText

java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView$Adapter.notifyDataSetChanged()' on a null object reference
at com.example.barryblack.FragmentPage.InsertItem(FragmentPage.java:60)
at com.example.barryblack.FragmentPage$1.onClick(FragmentPage.java:43)

答案1

得分: 0

这段代码：

private RecyclerView.Adapter mAdapter;

需要修改为：

private MyAdapter mAdapter;

以及将这段代码：

RecyclerView.Adapter adapter = new MyAdapter(countries);

修改为：

MyAdapter mAdapter = new MyAdapter(countries);
英文:

this code private RecyclerView.Adapter mAdapter;

must be private MyAdapter mAdapter;

and this RecyclerView.Adapter adapter = new MyAdapter(countries);

to this MyAdapter mAdapter = new MyAdapter(countries);

huangapple
  • 本文由 发表于 2020年4月6日 01:22:01
  • 转载请务必保留本文链接：https://java.coder-hub.com/61046534.html
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