从未分配私有字段“showGuess”答案

【问题标题】：Private field 'showGuess' never assigned从未分配私有字段“showGuess”
【发布时间】：2020-05-13 18:51:23
【问题描述】：

我已经为按钮 showGuess 初始化并创建了一个监听器。顺便说一句，应用程序崩溃

public class MainActivity extends AppCompatActivity {

private Button showGuess;

public MainActivity(Button showGuess) {
    this.showGuess = showGuess;
}


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

    showGuess.findViewById(R.id.button_name);

    showGuess.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, ShowGuess.class); 
           startActivity(intent);
        }
    });
}
}

这是调试部分中写的错误/警告：

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“android.view.View android.widget.Button.findViewById(int)”

【问题讨论】：

标签： android android-studio android-intent

【解决方案1】：

稍微修改一下：

public class MainActivity extends AppCompatActivity {

private Button showGuess;

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

    showGuess=findViewById(R.id.button_name);

    showGuess.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, ShowGuess.class); 
           startActivity(intent);
        }
    });
}
}

【讨论】：