概念
Fragment (碎片)
Fragment是Android3.0新增的,它與Activity十分相似,可以說成是微小版的activity,但不能等同於。用來在一個Activity中描述一些行爲或一部分用戶界面。使用多個Fragment可以在一個單獨的Activity中建立多個UI面板,也可以在多個Activity中使用Fragment。
可以把Fragment當成Activity的一個界面的一個組成部分,甚至Activity的界面可以完全有不同的Fragment組成,更重要的是Fragment擁有自己的生命週期和接收、處理用戶的事件,這樣就不必在Activity寫一堆控件的事件處理的代碼了。還可以動態的添加、替換和移除某個Fragment。
生命週期
一個Fragment必須是被嵌入到一個Activity中,它的生命週期直接被其所屬的宿主Activity生命週期影響,它的狀態會隨宿主的狀態變化而變化。Fragment的生命週期和它所在的Activity是密切相關的。如果Activity是暫停狀態,其中所有的Fragment都是暫停狀態;如果Activity是stopped狀態,這個Activity中所有的Fragment都不能被啓動;如果Activity被銷燬,那麼它其中的所有Fragment都會被銷燬。但是,當Activity在活動狀態,可以獨立控制Fragment的狀態
簡單的fragment跳轉小樣例
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", "我又發現", "實驗教學準備兼職", "兼職文員", "此羣涉嫌違規禁止訪問",
"京東JD.COM", "test", "test", "test", "test", "test"};
String[] co = {"馬上看完了", "312", "http://ffm.qq.com", "學剛:新年快樂", "鹿訂記結賬小姐姐:[OK]",
"徐一凡:[發呆]", "iPhone全場搶卷立減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) {
// 創建item,及其緩存類
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 {//緩存處理4級
public TextView name;
public TextView content;
public TextView time;
public ImageView pic;
public MyRcycleviewhoder(@NonNull View itemView) {
super(itemView);//初始化模塊
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文件和此處幾乎一樣。