Fragment之间的切换

利用Fragment实现界面跳转的功能，完成效果图如图：

主界面代码如下:

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:id="@+id/activity_main"    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="cn.edu.niit.pageredirecting.MainActivit<LinearLayo    android:id="@+id/show"

    android:layout_width="match_parent"    android:layout_height="0dp"    android:orientation="vertical"    android:layout_weight="1">

</LinearLayout>

<LinearLayout    android:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="0dp"    android:layout_weight="1">

<Button        android:id="@+id/bt_show"        android:layout_width="250dp"        android:layout_height="wrap_content"        android:text="@string/bt_show"        android:layout_gravity="center_horizontal"        android:gravity="center"        android:onClick="onClick"        /></LinearLayout>

</LinearLayout>第一个Fragment的布局代码：<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  tools:context="com.example.a15083.fragmentandactivity.FirstFragment"> <TextView  android:layout_width="match_parent"  android:layout_height="match_parent"  

android:gravity="center"  android:textSize="25sp"  android:text="@string/first_fragment" /> </FrameLayout>第二个Fragment布局代码：<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  tools:context="com.example.a15083.fragmentandactivity.SecondFragment"> <TextView  android:layout_width="match_parent"  android:layout_height="match_parent"  android:background="@color/colorAccent"  android:gravity="center"  android:text="@string/second_fragment"  android:textSize="25sp" /> </FrameLayout>Java部分代码如下：

package cn.edu.niit.pageredirecting;

        import android.app.FragmentManager;        import android.app.FragmentTransaction;        import android.support.v7.app.AppCompatActivity;        import android.os.Bundle;        import android.view.KeyEvent;        import android.view.View;        import android.widget.Toast;

public class FragmentActivity extends AppCompatActivity implements View.OnClickListener{    FirstFragment firstFragment;    SecondFragment secondFragment;    private boolean a=true;     //a的作用就是来判断第二次点击按钮时是否切换fragment    boolean e=false;        //e的作用是用来在第一个fragment点击返回时就执行退出程序操作

@Override    protected void onCreate(Bundle savedInstanceState)  {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_fragment);

FragmentManager manager = getFragmentManager();        FragmentTransaction transaction = manager.beginTransaction();        firstFragment = new FirstFragment();        transaction.add(R.id.show,firstFragment);        transaction.commit();    }

@Override    public void onClick(View view) {        if(view.getId()==R.id.bt_show){            e=true; //将e的值设置为true,使在点击返回键时能够切换fragment            if(a){                FragmentManager manager = getFragmentManager();                FragmentTransaction transaction = manager.beginTransaction();                if (secondFragment == null){                    secondFragment = new SecondFragment();                    transaction.replace(R.id.show,secondFragment);                    transaction.commit();                    a=false;    //设置a为false,使在第二次以后点击按钮能够弹出提示                } else{                    transaction.replace(R.id.show,secondFragment);                    transaction.commit();                    a=false;    //设置a为false,使在第二次以后点击按钮能够弹出提示                }            }else{                Toast.makeText(this,"This is second fragment",Toast.LENGTH_SHORT).show();            }        }    }

@Override    public boolean onKeyDown(int keyCode, KeyEvent event) {        if(event.getKeyCode()==KeyEvent.KEYCODE_BACK&&e){            FragmentManager manager = getFragmentManager();            FragmentTransaction transaction = manager.beginTransaction();            a=true;     //设置a为true,以便是点击按钮时能再次切换fragment            e=false;    //设置e为false,使在第一个fragment时能够退出            transaction.replace(R.id.show,firstFragment);            transaction.commit();            return  false;        } else {            finish();        }        return super.onKeyDown(keyCode, event);    }