问：如何实现通过接口，将接口赋值给fragment
答：1.定义一个接口，2.在fragment内定义这个接口的函数，3.在mainactivity内通过匿名内部类实现这个接口内的所有方法
如图：
一、压缩包
二、Activity与Fragment通信
1.原生方案：Bundle
2.java语言中类与类自己通信常用方案：接口
3.其它方案：eventBus，LiveData…（设计模式：观察者，发布订阅）
三、通过接口的实现步骤
1.定义接口，实现接口传值的两个方法
2.定义Callback函数，方便在mainactivity内创建匿名内部类，实现接口的函数
3.实现接口内的所有方法
4.在片段添加一个按钮，进行传值
5.实现fragment与activity之间的传值
6.在activity内进行接收fragment传过来的信息
7.在fragment内进行接收，activity传过来的信息
四、整体代码
1.布局fragment_blank_fragment1.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:layout_width="match_parent"android:layout_height="match_parent"tools:context=".fragment.BlankFragment1"><!-- TODO: Update blank fragment layout --><TextViewandroid:layout_width="match_parent"android:layout_height="match_parent"android:text="@string/hello_blank_fragment" /><Buttonandroid:layout_width="match_parent"android:layout_height="wrap_content"android:id="@+id/btn_three"android:text="数据传递"android:layout_marginTop="30dp"/></FrameLayout>
2.IFragmentCallback文件代码
package com.example.fragmentmanagers;public interface IFragmentCallback {//1.定义两个接口，第一个用于fragment去发信息给activity，第二个用于activity发信息给fragmentvoid sendMsgToActivity(String msg);String getMsgFromActivity(String msg);}
3.BlankFragment1文件代码
package com.example.fragmentmanagers.fragment;import android.os.Bundle;import androidx.fragment.app.Fragment;import android.util.Log;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.Button;import android.widget.Toast;import com.example.fragmentmanagers.IFragmentCallback;import com.example.fragmentmanagers.R;public class BlankFragment1 extends Fragment {//2.定义Callback变量private IFragmentCallback fragmentCallback;private View rootview;//3.定义Callback函数，方便给接口定义的两个函数赋值public void setFragmentCallback(IFragmentCallback callback){fragmentCallback=callback;}private static final String TAG = "BlankFragment1";@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);Bundle bundle = getArguments();String message = bundle.getString("message");Log.e("he",""+message);}@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {//5.绘制布局，将控件绑定，点击之后，发送消息if (rootview==null) {rootview=inflater.inflate(R.layout.fragment_blank_fragment1, container, false);}Button btn_three = rootview.findViewById(R.id.btn_three);btn_three.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// fragmentCallback.sendMsgToActivity("hello,I am from fragment");String msg = fragmentCallback.getMsgFromActivity("null");Toast.makeText(BlankFragment1.this.getContext(), ""+msg, Toast.LENGTH_SHORT).show();}});return rootview;}@Overridepublic void onResume() {super.onResume();}}
4.MainActivity文件代码
package com.example.fragmentmanagers;import androidx.appcompat.app.AppCompatActivity;import androidx.fragment.app.Fragment;import androidx.fragment.app.FragmentManager;import androidx.fragment.app.FragmentTransaction;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.Toast;import com.example.fragmentmanagers.fragment.BlankFragment1;import com.example.fragmentmanagers.fragment.BlankFragment2;public class MainActivity extends AppCompatActivity implements View.OnClickListener {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);Button btn_one = findViewById(R.id.btn_one);btn_one.setOnClickListener(this);Button btn_two = findViewById(R.id.btn_two);btn_two.setOnClickListener(this);}@Overridepublic void onClick(View v) {switch (v.getId()) {case R.id.btn_one:Bundle bundle = new Bundle();bundle.putString("message","我很喜欢享学课堂");BlankFragment1 blankFragment1 = new BlankFragment1();blankFragment1.setArguments(bundle);//4.在主活动内实现fragment这个对象内接口的所有方法blankFragment1.setFragmentCallback(new IFragmentCallback() {@Overridepublic void sendMsgToActivity(String msg) {Toast.makeText(MainActivity.this," "+msg, Toast.LENGTH_SHORT).show();}@Overridepublic String getMsgFromActivity(String string) {return "hello,I am from activity";}});replaceFragment(blankFragment1);break;case R.id.btn_two:replaceFragment(new BlankFragment2());}}//动态切换fragmentprivate void replaceFragment(Fragment fragment) {FragmentManager fragmentManager = getSupportFragmentManager();FragmentTransaction transaction = fragmentManager.beginTransaction();transaction.replace(R.id.fl_item,fragment);transaction.addToBackStack(null);transaction.commit();}}
5.效果图：
（1）从fragment到activity<br /><br /> （2）从activity到fragment<br />
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