按钮动作-Android应用程序

Question

我正在练习本书Hello，Android ed3.There有一个示例代码，用于创建一个动作按钮以显示'关于'游戏。我编辑了所有必需的xml文件。我收到错误在下面的代码中.logcat显示第10行的空指针异常：about.Button.setClickListener（this）。请帮助。另外我一直无法理解'this'参数。任何hep？

public class Sudoku extends Activity implements OnClickListener { 
private static final String TAG = "Sudoku"; 
    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 
     // Set up click listeners for all the button 
     View aboutButton = findViewById(R.id.about_button); 
     aboutButton.setOnClickListener(this); 

    } 

    public void onClick(View v) { 
      switch (v.getId()) { 
      case R.id.about_button: 
      Intent i = new Intent(this, About.class); 
      startActivity(i); 
      break; 
    } 

}}

Answer 1

看起来你没有 “about_button” 在xml文件按钮。你在xml中为按钮命名了吗？

Answer 2

public class Sudoku extends Activity implements OnClickListener { 
private static final String TAG = "Sudoku"; 
/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    // Set up click listeners for all the button 
    Button aboutButton = (Button) findViewById(R.id.about_button); 
    aboutButton.setOnClickListener(this); 

}

public void onClick(View v) { 
     if(v == aboutButton){ 
     Intent i = new Intent(this, About.class); 
     startActivity(i); 
     break; 
} 

试试这个...只是改变2-3行...