使用add与hide切换fragment

首先，在activity中添加方法（参数fragment是将要切换的fragment，变量mcContent是用来区分当前fragment和将要切换的fragment的）

public void switchFm(BaseFragment fragment) {
    if (fragment != mContent) {
        FragmentTransaction ft = fm.beginTransaction();
        if (fragment.isAdded()) {
            ft.hide(mContent).show(fragment).commit();
        } else {
            if (mContent == null) {
                ft.add(R.id.fl_content, fragment).commit();
            } else {
                ft.hide(mContent).add(R.id.fl_content, fragment).commit();
            }
        }
        mContent = fragment;
    }
}

在activity中调用：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    fm = getSupportFragmentManager();
    RadioGroup rgHelloworld = (RadioGroup) findViewById(R.id.rg_helloworld);
    rgHelloworld.setOnCheckedChangeListener(this);
    rgHelloworld.check(R.id.hello);
}

切换方法（实现RadioGroup的OnCheckedChangeListener监听）：

@Override
public void onCheckedChanged(RadioGroup radioGroup, int checkedID) {
    switch (checkedID) {
        case R.id.hello:
            switchFm(new HelloFragment());
            break;
        case R.id.world:
            switchFm(new WorldFragment());
            break;
    }
}

由此就可以自如的切换fragment

附xml文件：

       <?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/fl_top_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.kang.fragmentdemo.MainActivity">

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <android.support.v7.widget.Toolbar
        android:layout_width="match_parent"
        android:layout_height="48dp"
        android:background="#4250a7">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:orientation="horizontal">

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/app_name"
                android:textColor="#ffffff"
                android:textSize="22sp" />
        </LinearLayout>
    </android.support.v7.widget.Toolbar>

    <FrameLayout
        android:id="@+id/fl_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <RadioGroup
            android:id="@+id/rg_helloworld"
            android:layout_width="match_parent"
            android:layout_height="48dp"
            android:layout_gravity="bottom"
            android:orientation="horizontal">

            <RadioButton
                android:id="@+id/hello"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="@drawable/bg_radiobutton"
                android:button="@null"
                android:gravity="center"
                android:text="hello"
                android:textColor="#ffffff" />

            <RadioButton
                android:id="@+id/world"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="@drawable/bg_radiobutton"
                android:button="@null"
                android:gravity="center"
                android:text="world"
                android:textColor="#ffffff" />

        </RadioGroup>

    </FrameLayout>
</LinearLayout>
</FrameLayout>

附效果图：