Android 4.4的activity_main.xml与fragment_main.xml出现的资源问题

获取fragment_main.xml布局控件出现异常的解决办法：
    Android3.0以后新建的Android应用包含了两个xml布局文件，一个为activity_main.xml，另外一个fragment_main.xml，这样就可以实现UI的分片处理，我们以后就可以在fragment_main.xml上面添加控件等等。对于新手来说，可能在fragment_main.xml上面添加控件了，但是获取资源的操作却放在了应用的MainActivity的onCreate方法里面，而该方法里面却只加载了activity_main.xml文件，所以此时在这里面获取fragment_main.xml里面的资源，肯定是获取不到的，使用findByViewId获取到的值为NULL，其实对于fragment_main.xml， 是通过public static class PlaceholderFragment extends Fragment 里面的onCreateView方法来加载的，所以获取资源的方法应该放在onCreateView里面，给大家贴一个例子：

package com.example.activitydemo;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.os.Build;
import android.util.Log;

public class MainActivity extends ActionBarActivity {

    private static final String TAG = "ActivityDemo";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

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

        Log.e(TAG, "start onCreate~~~");
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.e(TAG, "start onStart~~~");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.e(TAG, "start onRestart~~~");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.e(TAG, "start onResume~~~");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.e(TAG, "start onPause~~~");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.e(TAG, "start onStop~~~");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.e(TAG, "start onDestroy~~~");
    }

    @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);

            Button button = (Button)rootView.findViewById(R.id.button_normal);

            button.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View arg0) {
                    // TODO Auto-generated method stub
                    Intent intent = new Intent(getActivity(), SecondActivity.class);
                    startActivity(intent);
                }
            });
            return rootView;
        }
    }

}

fragment_main.xml

<RelativeLayout xmlns:android=""
    xmlns:tools=""
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.activitydemo.MainActivity$PlaceholderFragment" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <EditText
        android:id="@+id/editText"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/button_normal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/editText"
        android:layout_below="@+id/editText"
        android:layout_marginLeft="25dp"
        android:layout_marginTop="90dp"
        android:text="页面普通跳转" />

</RelativeLayout>