使用fragment兼容低版本的写法

  [1]定义fragment继承V4包中的Fragment 

  [2]定义的activity要继承v4包中的FragmentActivity

  [3]通过这个方法getSupportFragmentManager  获取Fragment的管理者

 

import android.os.Bundle;
import android.annotation.SuppressLint;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.WindowManager;

@SuppressLint("CommitTransaction")
public class MainActivity extends FragmentActivity {

    @SuppressWarnings("deprecation")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // [1]获取手机的宽和高 windommanager
        WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
        int width = wm.getDefaultDisplay().getWidth();
        int height = wm.getDefaultDisplay().getHeight();
        // [2]判断横竖屏

        // [3.1]如果使用v4包中的fragment 获取fragment的管理者 是通过getsupportFragmentManager();
        FragmentManager supportFragmentManager = getSupportFragmentManager();

        // [3.2]开启一个事务
        FragmentTransaction transaction = supportFragmentManager.beginTransaction();

        if (height > width) {
            // 说明是竖屏 androind 代表系统定义好的 android.R.id.content理解成是当前手机的窗体
            transaction.replace(android.R.id.content, new Fragment1());

        } else {
            // 横屏
            transaction.replace(android.R.id.content, new Fragment2());
        }

        //[4]一定要记得 提交commit
        transaction.commit();

    }

}