在方法中实现ClickListener上的按钮

Question

我在尝试实现onClickListener时遇到错误，这是错误：03-06 19:21:20.432:E/AndroidRuntime（1197）：由java.lang.NullPointerException引起03-06 19:21:20.432:E/AndroidRuntime（1197）：在com.coursework.braintrain.Game.Easy12（Game.java:186）

这是导致它的行：buttonhash.setOnClickListener（new OnClickListener{

基本上，我在onCreate（）方法中制作了buttonhash，但我想让它在按下按钮时监听用户输入的内容是否与方程的实际答案匹配。也许如果我只是把代码放上去，它会更有意义（不善于解释…）

public class Game extends Activity {
private static final String TAG = "Brain Training";
public static final String KEY_DIFFICULTY = "com.coursework.braintrain.difficulty";
public static final int DIFFICULTY_EASY = 0;
public static final int DIFFICULTY_MEDIUM = 1;
public static final int DIFFICULTY_HARD = 2;
public static final int DIFFICULTY_GURU = 3;

private int brain;
private EditText edittext;
private Button button1;
private Button button2;
private Button button3;
private Button button4;
private Button button5;
private Button button6;
private Button button7;
private Button button8;
private Button button9;
private Button button0;
private TextView answerLabel;
private Button buttonhash;

@Override
protected void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    Log.d(TAG, "onCreate");
    setContentView(R.layout.gamelayout);
    int diff = getIntent().getIntExtra(KEY_DIFFICULTY, DIFFICULTY_EASY);
    getGame(diff);

    edittext = (EditText) findViewById(R.id.USERentry);
    answerLabel = (TextView) findViewById(R.id.rightwrong_label);
    button1 = (Button) findViewById(R.id.keypad_1);
    button1.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            // Perform action on clicks
            //String buttonText = (String) button.getText();
            edittext.setText(edittext.getText() + "1");
            //edittext.setText() = edittext.getText() + "1";
        }
    });
    button2 = (Button) findViewById(R.id.keypad_2);
    button2.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "2");
        }
    });
    button3 = (Button) findViewById(R.id.keypad_3);
    button3.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "3");
        }
    });
    button4 = (Button) findViewById(R.id.keypad_4);
    button4.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "4");
        }
    });
    button5 = (Button) findViewById(R.id.keypad_5);
    button5.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "5");
        }
    });
    button6 = (Button) findViewById(R.id.keypad_6);
    button6.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "6");
        }
    });
    button7 = (Button) findViewById(R.id.keypad_7);
    button7.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "7");
        }
    });
    button8 = (Button) findViewById(R.id.keypad_8);
    button8.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "8");
        }
    });
    button9 = (Button) findViewById(R.id.keypad_9);
    button9.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "9");
        }
    });
    button0 = (Button) findViewById(R.id.keypad_0);
    button0.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            edittext.setText(edittext.getText() + "0");
        }
    });
    buttonhash = (Button) findViewById(R.id.keypad_hash);

    //final Button buttonDel = (Button) findViewById(R.id.keypad_del);
    //buttonDel.setOnClickListener(new OnClickListener(){
        //public void onClick(View v){
            //edittext.setText(edittext.getText() - 1);
        //}
    //});
}

private void getGame（int diff）｛

    //TODO: Continue last game
    switch(diff){
    case DIFFICULTY_HARD:
        break;
    case DIFFICULTY_MEDIUM:
        break;
    case DIFFICULTY_EASY:
        Easy12();
        break;
    }
    //might require to return an array or something
}
public void Easy12(){
    Random rand = new Random();
    int a = (int) rand.nextInt(100)+1;
    int b = (int) rand.nextInt(100)+1;
    final TextView tv = (TextView) findViewById(R.id.question_label);
    String aString = Integer.toString(a);
    String bString = Integer.toString(b);
    String display = aString + " + " + bString + " =";
    tv.setText(display);
    final int c = a + b;
    buttonhash.setOnClickListener(new OnClickListener(){ //HERE IS THE ERROR!!
        public void onClick(View v) {
            if(edittext.getText().toString().equals(String.valueOf(c))){
                answerLabel.setText(R.string.answer_correct);
                answerLabel.setTextColor(R.color.correct_color);
                //answerLabel.setBackgroundColor(R.color.background_answer);
            }
            else
            {
                answerLabel.setText(R.string.answer_wrong);
                answerLabel.setTextColor(R.color.wrong_color);
                //answerLabel.setBackgroundColor(R.color.background_answer);
            }
        }
    });
}

}

我的XML很好，如果这是可能导致它的原因之一，但我不认为它与它有任何关系：p

所以我的问题是在我设置buttonhash的onClickListener的那一行得到一个nullpointerexception，它在另一个方法（Easy12（））中。如果您能提供任何可能导致这种情况/如何解决的帮助，我们将不胜感激。感谢

Answer 1

您在定义按钮之前调用getGame（），因此它为null。将按钮声明放在getGame上面，如下所示：

buttonhash = (Button) findViewById(R.id.keypad_hash);
getGame(diff)

Answer 2

如果它在那一行崩溃，那么buttonhash为null。由于某些原因，当您在Oncreate中调用findViewById时，它没有被设置/找到。确保id与xml中的id匹配。

请确保在初始化getGame后也调用它。

Answer 3

将buttonhash.setOnClickListener（新的OnClickLister（）更改为

buttonhash.setOnClickListener（新的Veiw.OnClickListener（）