android - 从未分配私有字段“showGuess”

Question

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

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);
        }
    });
}
}

这是调试部分中编写的错误/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)”

标签： androidandroid-studioandroid-intent

Answer 1

一点编辑：

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);
        }
    });
}
}