Question

我的问题在第39行，它是空异常

btnDetail = findViewById(R.id.btn_move_activity);
        btnDetail.setOnClickListener(this);

我的代码

package com.example.aplikasimoviecataloguesub1;

import android.content.Intent;
import android.content.res.TypedArray;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    Button btnDetail;
    private String[] dataName;
    private String[] dataDescription;
    private String[] dataDate;
    private TypedArray dataPhoto;
    private MoviesAdapter adapter;
    private ArrayList<Movie> movies;


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

        adapter = new MoviesAdapter(this);

        ListView listView = findViewById(R.id.lv_list);
        listView.setAdapter(adapter);

        prepare();
        addItem();

        btnDetail = findViewById(R.id.btn_move_activity);
        btnDetail.setOnClickListener(this);
    }


    private void prepare() {
        dataName = getResources().getStringArray(R.array.data_name);
        dataDescription = getResources().getStringArray(R.array.data_description);
        dataDate = getResources().getStringArray(R.array.data_date);
        dataPhoto = getResources().obtainTypedArray(R.array.data_photo);
    }

    private void addItem() {
        movies = new ArrayList<>();
        for (int i = 0; i < dataName.length; i++) {
            Movie movie = new Movie();
            movie.setPhoto(dataPhoto.getResourceId(i, -1));
            movie.setName(dataName[i]);
            movie.setDate(dataDate[i]);
            movie.setDescription(dataDescription[i]);
            movies.add(movie);
        }
        adapter.setMovies(movies);
    }


    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.btn_move_activity:
                Intent moveIntent = new Intent(MainActivity.this, DetailActivity.class);
                startActivity(moveIntent);
                break;
        }
    }
}

这是错误

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.example.aplikasimoviecataloguesub1.MainActivity.onCreate(MainActivity.java:39)

Answer 1

确保R.id.btn_move_activity这个ID的视图来自R.layout.activity_main这个文件。

Answer 2

检查id所传递的button。根据崩溃，您正在初始化button之前对其进行访问。这就像访问内存中不存在的内容。因此， NPE 。另外，请养成在致电views后立即初始化所有setContentView()的习惯。有了这种习惯，您就可以避免 NPE对视图的偏爱 。请参考下面的代码：

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

        initViews();
        initListeners();

        adapter = new MoviesAdapter(this);

        listView.setAdapter(adapter);

        prepare();
        addItem();

    }



    private void initViews() {
        listView = findViewById(R.id.lv_list);
        btnDetail = findViewById(R.id.btn_move_activity);

    }

    private void initListeners() {
        btnDetail.setOnClickListener(this);
    }

如果您有任何困惑，请告诉我。快乐编码：）

Answer 3

您必须将变量强制转换为相关的视图元素，如下所示

jars

我想在按下按钮时进行其他活动

3 个答案: