Android在片段之间传递数据

在本教程中，我们将开发一个包含TabLayout、ViewPager和Fragments的应用程序。我们将实现一种功能，可以将数据从一个Fragment传递到另一个Fragment。

在Android中，在片段之间传递数据

只能在活动级别上使用意图来发送数据。要在片段之间传递数据，我们需要创建自己的接口。下面是从一个片段到另一个片段发送字符串数据的流程。让我们开始实现上述流程。

安卓在片段之间传递数据的项目结构

下面给出了MainActivity.java类的xml布局。

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="https://schemas.android.com/apk/res/android"
    xmlns:app="https://schemas.android.com/apk/res-auto"
    xmlns:tools="https://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.Olivia.passingdatabetweenfragments.MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            style="@style/MyStyle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabGravity="fill"
            app:tabMode="fixed" />

    </android.support.design.widget.AppBarLayout>


    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />


</android.support.design.widget.CoordinatorLayout>

TabLayout和ToolBar的样式在styles.xml文件中定义，如下所示。

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

    <style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />

    <style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />

    <style name="MyStyle" parent="Widget.Design.TabLayout">
        <item name="tabIndicatorColor">#FFFF</item>
        <item name="tabIndicatorHeight">5dp</item>
        <item name="tabPaddingStart">8dp</item>
        <item name="tabPaddingEnd">8dp</item>
    </style>

</resources>

ViewPagerAdapter.java是初始化Fragment的地方。以下是代码。

public class ViewPagerAdapter extends FragmentPagerAdapter {

    public ViewPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        Fragment fragment = null;
        if (position == 0) {
            fragment = new FragmentOne();
        } else if (position == 1) {
            fragment = new FragmentTwo();
        }
        return fragment;
    }

    @Override
    public int getCount() {
        return 2;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        String title = null;
        if (position == 0) {
            title = "Tab-1";
        } else if (position == 1) {
            title = "Tab-2";
        }
        return title;
    }
}

在FragmentOne中，将EditText中输入的数据发送到FragmentTwo。下面是fragment_one.xml的XML布局。

<?xml version="1.0" encoding="utf-8"?>

<ScrollView xmlns:android="https://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:fillViewport="true">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">


        <EditText
            android:id="@+id/inMessage"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_above="@+id/btnPassData"
            android:layout_margin="16dp"
            android:hint="Enter here" />

        <Button
            android:id="@+id/btnPassData"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:text="PASS DATA TO FRAGMENT TWO" />


    </RelativeLayout>
</ScrollView>

下面给出了fragment_two.xml的xml布局。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/txtData"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:layout_centerInParent="true"
        android:text="No data received" />


</RelativeLayout>

以下是FragmentOne.java类的代码。

package com.Olivia.passingdatabetweenfragments;

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;

public class FragmentOne extends Fragment {

    SendMessage SM;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(
                R.layout.fragment_one, container, false);
        return rootView;


    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        Button btnPassData = (Button) view.findViewById(R.id.btnPassData);
        final EditText inData = (EditText) view.findViewById(R.id.inMessage);
        btnPassData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SM.sendData(inData.getText().toString().trim());
            }
        });

    }

    interface SendMessage {
        void sendData(String message);
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);

        try {
            SM = (SendMessage) getActivity();
        } catch (ClassCastException e) {
            throw new ClassCastException("Error in retrieving data. Please try again");
        }
    }
}

在上面的onAttach方法中初始化了名为SendMessage的自定义接口。这个接口将会在接下来我们即将看到的MainActivity.java中被实现。FragmentTwo.java类的代码如下所示。

package com.Olivia.passingdatabetweenfragments;


import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class FragmentTwo extends Fragment {

    TextView txtData;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(
                R.layout.fragment_two, container, false);
        return rootView;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        txtData = (TextView)view.findViewById(R.id.txtData);
    }

    protected void displayReceivedData(String message)
    {
        txtData.setText("Data received: "+message);
    }
}

在MainActivity.java中，从自定义接口的方法中调用FragmentTwo.java实例上的displayReceivedData()。

package com.Olivia.passingdatabetweenfragments;

import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;

public class MainActivity extends AppCompatActivity implements FragmentOne.SendMessage{

    TabLayout tabLayout;
    ViewPager viewPager;
    ViewPagerAdapter viewPagerAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        viewPager = (ViewPager) findViewById(R.id.viewPager);
        viewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager());
        viewPager.setAdapter(viewPagerAdapter);
        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);
    }

    @Override
    public void sendData(String message) {
        String tag = "android:switcher:" + R.id.viewPager + ":" + 1;
        FragmentTwo f = (FragmentTwo) getSupportFragmentManager().findFragmentByTag(tag);
        f.displayReceivedData(message);
    }
}

以上代码中的sendData（）方法在FragmentOne中的按钮被按下时被触发。我们使用findFragmentByTag方法获取已经在ViewPagerAdapter中初始化的FragmentTwo。上述应用程序的输出如下所示。这就结束了本教程。您可以从下面的链接下载最终的Android PassingDataBetweenFragments项目。

下载安卓传递数据的Fragment示例项目

参考：碎片化沟通