问题描述
我有以下活动:
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new StartFragment())
.commit();
}
Button login = (Button) findViewById(R.id.loginButton);
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent intent = new Intent(MainActivity.this,LoginActivity.class);
startActivity(intent);
}
});
}
当我尝试为 R.id.loginButton 调用 findViewByID 时，我得到了一个 NPE，我猜这是因为 loginButton在一个单独的片段中，我有:
I get a NPE when I try to invoke findViewByID for R.id.loginButton, and I'm guessing this is because loginButton is within a separate Fragment, which I have as:
public static class StartFragment extends Fragment {
public StartFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_main, container, false);
}
}
但是，我不确定如何解决此问题以便我可以找到 loginButton ID.我以前没有使用过片段，所以我意识到我可能正在错误地使用它们/实现它们.fragment_main 在 LinearLayout 中包含几个按钮，而 activity_main 只有一个 FrameLayout.
However, I am unsure of how to fix this so that I can find the loginButton ID. I haven't worked with fragments before, so I realize I may be using them/implementing them incorrectly. fragment_main contains a few buttons in a LinearLayout, and activity_main has nothing but a single FrameLayout.
推荐答案
编写代码以从片段初始化按钮，因为您的按钮是在片段布局中而不是在活动的布局中.
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
Button login = (Button) rootView.findViewById(R.id.loginButton);
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent intent = new Intent(MainActivity.this,
LoginActivity.class);
startActivity(intent);
}
});
return rootView;
}
并从Activity的onCreate中删除登录按钮相关的代码.
And remove the login button related code from onCreate of Activity.
这篇关于尝试 findViewById 时抛出 Nullpointerexception的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！