Question

所以我有这个代码，现在我添加了一个简单的动作到按钮添加（setOnClickListener），当我运行应用程序时，它立即崩溃... 知道为什么吗？

public class MainActivity extends ActionBarActivity {

int counter;
Button add,sub;
TextView display;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    counter = 0;
    add = (Button)findViewById(R.id.bAdd);
    sub = (Button)findViewById(R.id.bSub);
    display = (TextView)findViewById(R.id.tvDisplay);

    add.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            counter++;
            display.setText("Your Total is " + counter);
        }
    });

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment())
                .commit();
    }
} 


@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        return rootView;
    }
}

}

Answer 1

最有可能是你的

add = (Button)findViewById(R.id.bAdd);

正在返回null。尝试通过打印验证这一点

Log.d("TEST", "is null: " + (add == null));

下一步是确保您的 activity_main XML中确实定义了ID为“bAdd”的Button。编辑您的问题以添加您的XML文件activity_main。

应用程序在创建一个简单的按钮后崩溃

1 个答案: