Fragment之間的切換

利用Fragment實現界面跳轉的功能，完成效果圖如圖：

主界面代碼如下:

<?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>
第一個Fragment的布局代碼：
<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>
第二個Fragment布局代碼：
<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部分代碼如下：

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的作用就是來判斷第二次點擊按鈕時是否切換fragment
    boolean e=false;        //e的作用是用來在第一個fragment點擊返回時就執行退出程序操作

    @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; //將e的值設置為true,使在點擊返回鍵時能夠切換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;    //設置a為false,使在第二次以后點擊按鈕能夠彈出提示
                } else{
                    transaction.replace(R.id.show,secondFragment);
                    transaction.commit();
                    a=false;    //設置a為false,使在第二次以后點擊按鈕能夠彈出提示
                }
            }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;     //設置a為true,以便是點擊按鈕時能再次切換fragment
            e=false;    //設置e為false,使在第一個fragment時能夠退出
            transaction.replace(R.id.show,firstFragment);
            transaction.commit();
            return  false;
        } else {
            finish();
        }
        return super.onKeyDown(keyCode, event);
    }