Android学习之fragment

概念

Fragment （碎片）

         Fragment是Android3.0新增的，它与Activity十分相似，可以说成是微小版的activity，但不能等同于。用来在一个Activity中描述一些行为或一部分用户界面。使用多个Fragment可以在一个单独的Activity中建立多个UI面板，也可以在多个Activity中使用Fragment。
可以把Fragment当成Activity的一个界面的一个组成部分，甚至Activity的界面可以完全有不同的Fragment组成，更重要的是Fragment拥有自己的生命周期和接收、处理用户的事件，这样就不必在Activity写一堆控件的事件处理的代码了。还可以动态的添加、替换和移除某个Fragment。

生命周期

        一个Fragment必须是被嵌入到一个Activity中,它的生命周期直接被其所属的宿主Activity生命周期影响,它的状态会随宿主的状态变化而变化。Fragment的生命周期和它所在的Activity是密切相关的。如果Activity是暂停状态，其中所有的Fragment都是暂停状态；如果Activity是stopped状态，这个Activity中所有的Fragment都不能被启动；如果Activity被销毁，那么它其中的所有Fragment都会被销毁。但是，当Activity在活动状态，可以独立控制Fragment的状态

简单的fragment跳转小样例

activity

package com.example.myapplication3;

import androidx.annotation.DrawableRes;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    BlankFragment blankFragment = new BlankFragment();
    BlankFragment2 blankFragment2 = new BlankFragment2();
    BlankFragment3 blankFragment3= new BlankFragment3();
    BlankFragment4 blankFragment4= new BlankFragment4();



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = findViewById(R.id.button);
        getSupportFragmentManager().beginTransaction().replace(R.id.lin_layout,blankFragment).commit();

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getSupportFragmentManager().beginTransaction().replace(R.id.lin_layout,blankFragment).commit();

            }
        });
        Button button2 = findViewById(R.id.button2);
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getSupportFragmentManager().beginTransaction().replace(R.id.lin_layout,blankFragment2).commit();

            }
        });
        Button button3 = findViewById(R.id.button3);
        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getSupportFragmentManager().beginTransaction().replace(R.id.lin_layout,blankFragment4).commit();

            }
        });
        Button button4= findViewById(R.id.button4);
        button4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getSupportFragmentManager().beginTransaction().replace(R.id.lin_layout,blankFragment3).commit();

            }
        });



    }





}

blankfragment

package com.example.myapplication3;

import android.content.Context;
import android.net.Uri;
import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;



public class BlankFragment extends Fragment {
    List<Chat> list = new ArrayList<>();

    RecyclerView mRecyclerView;

    String[] na = {"秋秋", "彭彭彭彭", "我又发现", "实验教学准备兼职", "兼职文员", "此群涉嫌违规禁止访问",
            "京东JD.COM", "test", "test", "test", "test", "test"};
    String[] co = {"马上看完了", "312", "http://ffm.qq.com", "学刚：新年快乐", "鹿订记结账小姐姐：[OK]",
            "徐一凡：[发呆]", "iPhone全场抢卷立减700元", "test", "test", "test", "test", "test"};
    String[] ti = {"13:00", "星期二", "2020/1/27", "2020/1/1", "2019/4/27", "13:06：", "13:01", "test",
            "test", "test", "test", "test"};


    int[] id = new int[100];


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

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        mRecyclerView = getActivity().findViewById(R.id.recyclerView);

        id[0] = (int) R.drawable.b;
        id[1] = (int) R.drawable.a1;
        id[2] = (int) R.drawable.a2;
        id[3] = (int) R.drawable.a3;
        id[4] = (int) R.drawable.b1;
        id[5] = (int) R.drawable.b3;
        id[6] = (int) R.drawable.b4;
        id[7] = (int) R.drawable.b4;
        id[8] = (int) R.drawable.b4;
        id[9] = (int) R.drawable.b4;
        id[10] = (int) R.drawable.b4;
        id[11] = (int) R.drawable.b4;

        for (int i = 0; i < 12; i++) {
            Chat chat = new Chat();
            chat.name = na[i];
            chat.content = co[i];
            chat.time = ti[i];
            chat.pic = id[i];
            list.add(chat);

        }
        mRecyclerView.setAdapter(new Myadapter());
        //
        mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));


    }

    public class Myadapter extends RecyclerView.Adapter<MyRcycleviewhoder> {

        @NonNull
        @Override
        public MyRcycleviewhoder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
//        创建item，及其缓存类
            View view = LayoutInflater.from(getActivity()).inflate(R.layout.item_layout, parent, false);
            MyRcycleviewhoder myRcycleviewhoder = new MyRcycleviewhoder(view);
            return myRcycleviewhoder;
        }

        @Override
        public void onBindViewHolder(@NonNull MyRcycleviewhoder holder, int position) {
            Chat chat = list.get(position);

            holder.name.setText(chat.name);
            holder.content.setText(chat.content);
            holder.time.setText(chat.time);
            holder.pic.setImageDrawable(getResources().getDrawable((int) chat.pic));
        }

        @Override
        public int getItemCount() {
            return list.size();
        }
    }

    public class MyRcycleviewhoder extends RecyclerView.ViewHolder {//缓存处理4级

        public TextView name;
        public TextView content;
        public TextView time;
        public ImageView pic;

        public MyRcycleviewhoder(@NonNull View itemView) {

            super(itemView);//初始化模块

            name = itemView.findViewById(R.id.name);
            content = itemView.findViewById(R.id.content);
            time = itemView.findViewById(R.id.time);
            pic = itemView.findViewById(R.id.pic);
        }
    }
}

本案例的xml文件和此处几乎一样。