更新到Android 4.4，写了个小程序。发现运行不起来了。抛空指针异常。debug模式下，发现在onCreate方法中获取Button是null。
Android 4.4把layout进行了重组，全部放到了Fragment下，在onCreate方法执行时，Fragment还没有被调用，所以在这个方法中获取Fragment中的Button是空值。新类中多了一个Fragment的内部类，当xml的Fragment被装载时，会调用内部类的onCreateView方法，所以要将所有之前在layout中而现在移到fragment中的操作全部移到此方法中进行。
package com.bignerdranch.android.geoquiz;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;
public class TestActivity extends ActionBarActivity {
private static Button mFirstButton;
private static Button mSecondButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
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.test, 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) {
final View rootView = inflater.inflate(R.layout.fragment_test, container,
false);
mFirstButton = (Button) rootView.findViewById(R.id.first_button);
mFirstButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(rootView.getContext(), R.string.first_toast,
Toast.LENGTH_SHORT).show();
}
});
mSecondButton = (Button) rootView.findViewById(R.id.second_button);
mSecondButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(rootView.getContext(), R.string.second_toast,
Toast.LENGTH_SHORT).show();
}
});
return rootView;
}
}
}