在同一個(gè)地方跌倒兩次棘伴，才能體會(huì)到“好記性不如爛筆頭”！

一、Bundle簡(jiǎn)介

??bundle在Android開(kāi)發(fā)中非常常見(jiàn)驶悟，它的作用主要時(shí)用于傳遞數(shù)據(jù)；它所保存的數(shù)據(jù)是以key-value(鍵值對(duì))的形式存在的,也就是說(shuō)bundle是保存數(shù)據(jù)的容器材失，內(nèi)部使用了Arraymap去存儲(chǔ)數(shù)據(jù)痕鳍，也提供了很多get，put方法龙巨。
??bundle傳遞的數(shù)據(jù)包括：string笼呆、int、boolean旨别、byte诗赌、float、long昼榛、double等基本類(lèi)型或它們對(duì)應(yīng)的數(shù)組境肾，也可以是對(duì)象或?qū)ο髷?shù)組。當(dāng)bundle傳遞的是對(duì)象或?qū)ο髷?shù)組時(shí)胆屿，必須實(shí)現(xiàn)Serialiable或Parcelable接口奥喻。
??bundle主要用于以下3個(gè)場(chǎng)合：
??1. Activity狀態(tài)數(shù)據(jù)的保存與恢復(fù)，涉及到兩個(gè)回調(diào)：①void onSaveInstanceState(Bundle outState)非迹；② void onCreate(Bundle savedInstanceState)环鲤；
??2. Fragment的setArguments方法：void setArgument(Bundle args)；
??3. 消息機(jī)制中的Message的setData方法：void setData(Bundle data)憎兽。

二冷离、Bundle源碼解析

• 首先看下Bundle的聲明：
  public final class Bundle extends BaseBundle implements Cloneable, Parcelable
  ??從聲明中我們可以看出：①它使用了final進(jìn)行修飾，所以不可以被繼承纯命；②它實(shí)現(xiàn)了兩個(gè)接口Cloneable和Parcelable西剥，這就意味著它必須實(shí)現(xiàn)以下方法：
  ??1. public Object clone()
  ??2. public int describeContents()
  ??3. public void writeToParcel(Parcel parcel, int flags)
  ??4. public void readFromParcel(Parcel parcel)
  ??5. public static final Parcelable.Creator<Bundle> CREATOR = new Parcelable.Creator<Bundle>()
• 再看bundle的內(nèi)存結(jié)構(gòu)：
  ArrayMap<String, Object> mMap = null
  ??它使用的是ArrayMap，這個(gè)集合類(lèi)存儲(chǔ)的也是鍵值對(duì)亿汞，但是與Hashmap不同的是瞭空，hashmap采用的是“數(shù)組+鏈表”的方式存儲(chǔ)，而Arraymap中使用的是兩個(gè)數(shù)組進(jìn)行存儲(chǔ)疗我，一個(gè)數(shù)組存儲(chǔ)key咆畏，一個(gè)數(shù)組存儲(chǔ)value，內(nèi)部的增刪改查都將會(huì)使用二分查找來(lái)進(jìn)行吴裤，這個(gè)和SparseArray差不多旧找，只不過(guò)sparseArray的key值只能是int型的，而Arraymap可以是map型麦牺，所以在數(shù)據(jù)量不大的情況下可以使用這兩個(gè)集合代替hashmap去優(yōu)化性能钮蛛；

三鞭缭、Bundle繼承的方法

??Bundle操作的基本數(shù)據(jù)類(lèi)型如下表所示，它們都繼承自BaseBundle （From class android.os.BaseBundle ）

四愿卒、構(gòu)造方法

• Constructs a new, empty Bundle.
  Bundle()
• Constructs a new, empty Bundle that uses a specific ClassLoader for instantiating Parcelable and Serializable objects.
  Bundle(ClassLoader loader)
• Constructs a new, empty Bundle sized to hold the given number of elements. The Bundle will grow as needed.
  Bundle(Int capacity)
• Constructs a Bundle containing a copy of the mappings from the given Bundle. Does only a shallow copy of the original Bundle.
  Bundle(Int b)
• Constructs a Bundle containing a copy of the mappings from the given PersistableBundle. Does only a shallow copy of the PersistableBundle.
  Bundle(PersistableBundle b)

五缚去、實(shí)戰(zhàn)練習(xí)

1. 在Activity to Activity傳遞數(shù)據(jù)時(shí)使用Bundle

① 當(dāng)傳遞簡(jiǎn)單數(shù)據(jù)時(shí)

??新建一個(gè)MainActivity,對(duì)應(yīng)的布局文件比較簡(jiǎn)單，就是一個(gè)Button琼开，點(diǎn)擊這個(gè)按鈕后，程序跳轉(zhuǎn)到SecondActivity枕荞，并將傳遞的數(shù)據(jù)在SecondActivity的TextView中顯示出來(lái)柜候。這樣，就使用Bundle實(shí)現(xiàn)了數(shù)據(jù)在Activity之間的傳遞躏精。

package com.example.bundletest;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    //聲明控件對(duì)象
    private Button mButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //獲取控件的對(duì)象
        mButton = findViewById(R.id.button);

        //為Button綁定監(jiān)聽(tīng)器
        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                /**
                 * 存入數(shù)據(jù)
                 */
                //實(shí)例化一個(gè)Bundle
                Bundle bundle = new Bundle();
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);

                //設(shè)置數(shù)據(jù)
                String name = "Trump";
                int num = 123;

                //把數(shù)據(jù)放入到Bundle容器中
                bundle.putString("Name", name);
                bundle.putInt("Num", num);

                //把Bundle容器中的數(shù)據(jù)放到Intent中
                intent.putExtra("Message", bundle);

                //啟動(dòng)該Intent渣刷，實(shí)現(xiàn)Activity的跳轉(zhuǎn)
                startActivity(intent);
            }
        });
    }
}

??新建一個(gè)SecondActivity，用于顯示傳遞的數(shù)據(jù)矗烛。對(duì)應(yīng)的布局文件也很簡(jiǎn)單辅柴，就是一個(gè)TextView。

package com.example.bundletest;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;

public class SecondActivity extends AppCompatActivity {
    //聲明控件對(duì)象
    private TextView textView;

    @SuppressLint("SetTextI18n")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        //獲取控件的對(duì)象
        textView = findViewById(R.id.text_view);

        /**
         *讀取數(shù)據(jù)
         */
        Intent intent = getIntent();
        //從Intent中取出Bundle
        Bundle bundle = intent.getBundleExtra("Message");

        //獲取數(shù)據(jù)
        assert bundle != null;
        String name = bundle.getString("Name");
        int num = bundle.getInt("Num");

        //顯示數(shù)據(jù)
        textView.setText(name + "\n" + num);
    }
}

??運(yùn)行程序后瞭吃，結(jié)果如下圖所示：

??點(diǎn)擊Button碌嘀，結(jié)果如下圖所示：

② 當(dāng)傳遞的參數(shù)很多，或者傳遞一個(gè)類(lèi)的對(duì)象時(shí)

??新建一個(gè)JavaBean歪架，將這個(gè)類(lèi)命名為FunPerson股冗，并實(shí)現(xiàn)Serializable接口。

package com.example.bundletest;

import java.io.Serializable;

public class FunPerson implements Serializable {
    //創(chuàng)建實(shí)例變量
    private String name;
    private int num;

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setNum(int num) {
        this.num = num;
    }

    public int getNum() {
        return num;
    }
}

??修改MainActivity中的代碼：

public class MainActivity extends AppCompatActivity {
    //聲明控件對(duì)象
    private Button mButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //獲取控件的對(duì)象
        mButton = findViewById(R.id.button);

        //為Button綁定監(jiān)聽(tīng)器
        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                /**
                 * 存入數(shù)據(jù)
                 */
                FunPerson person = new FunPerson();
                //設(shè)置數(shù)據(jù)
                String name = "Trump is fun";
                int num = 12345;
                person.setName("name");
                person.setNum(num);

                //實(shí)例化一個(gè)Bundle
                Bundle bundle = new Bundle();
                //把FunPerson數(shù)據(jù)放入到Bundle容器中
                bundle.putSerializable("Person", person);

                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
                //把Bundle容器中的數(shù)據(jù)放到Intent中
                intent.putExtras(bundle);

                //啟動(dòng)該Intent和蚪，實(shí)現(xiàn)Activity的跳轉(zhuǎn)
                startActivity(intent);
            }
        });
    }
}

??修改SecondActivity中的代碼：

public class SecondActivity extends AppCompatActivity {
    //聲明控件對(duì)象
    private TextView textView;

    @SuppressLint("SetTextI18n")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        //獲取控件的對(duì)象
        textView = findViewById(R.id.text_view);

        /**
         *讀取數(shù)據(jù)
         */
        Intent intent = getIntent();
        //從Intent中取出Bundle
        Bundle bundle = intent.getExtras();

        //獲取FunPerson里的數(shù)據(jù)數(shù)據(jù)
        assert bundle != null;
        FunPerson person = (FunPerson)bundle.getSerializable("Person");

        assert person != null;
        String name = person.getName();
        int num = person.getNum();

        //顯示數(shù)據(jù)
        textView.setText(name + "\n" + num);
    }
}

??看下運(yùn)行后的結(jié)果：

2. 在Activity to Fragment傳遞數(shù)據(jù)時(shí)使用Bundle

??Activity重新創(chuàng)建時(shí)止状，會(huì)重新構(gòu)建它所管理的Fragment，原先的Fragment的字段值將會(huì)全部丟失攒霹，但是通過(guò)Fragment.setArguments(Bundle bundle)方法設(shè)置的bundle會(huì)保留下來(lái)怯疤。所以盡量使用Fragment.setArguments(Bundle bundle)方式來(lái)傳遞參數(shù)。
??有兩種實(shí)現(xiàn)方案：

① 方法一：使用Fragment的靜態(tài)方法newInstance()來(lái)傳遞數(shù)據(jù)

??新建MainActivity：

public class MainActivity extends AppCompatActivity {

    private Button mButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mButton = findViewById(R.id.button);

        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //發(fā)送數(shù)據(jù)
                BlankFragment blankFragment =  BlankFragment.newInstance("Message_1 To Fragment", "Message_2 To Fragment");
                FragmentManager fragmentManager = getSupportFragmentManager();
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                //FrameLayout用于動(dòng)態(tài)更新fragment
                fragmentTransaction.replace(R.id.frame_layout, blankFragment);
                fragmentTransaction.commit();
            }
        });
    }
}

??MainActivity的布局文件如下：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginTop="8dp"
        android:text="SendMsg"
        android:textAllCaps="false"
        app:layout_constraintBottom_toTopOf="@+id/guide_line"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guide_line"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_begin="255dp" />
    
    <FrameLayout
        android:id="@+id/frame_layout"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/guide_line"
        app:layout_constraintVertical_bias="0.0" >
    </FrameLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

??新建一個(gè)Fragment：

public class BlankFragment extends Fragment {
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;


    public static BlankFragment newInstance(String param1, String param2) {
        BlankFragment fragment = new BlankFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_blank, container, false);

        TextView textView = view.findViewById(R.id.text_view);
        //Fragment獲取數(shù)據(jù)
        Bundle bundle = getArguments();
        String message = null;
        if (bundle != null) {
            message = bundle.getString(ARG_PARAM1);
        }
        textView.setText(message);
        return view;
    }
}

??BlankFragment的布局文件比較簡(jiǎn)單催束，就是一個(gè)顯示用的TextView集峦。
??運(yùn)行程序，點(diǎn)擊Button泣崩，結(jié)果如下圖bundle4所示：

② 方法二：

??修改MainActivity的代碼：

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button mButton = findViewById(R.id.button);
        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //發(fā)送數(shù)據(jù)
                ToFragment fragment = new ToFragment();
                //新建一個(gè)Bundle實(shí)例
                Bundle bundle = new Bundle();
                bundle.putString("data", "From Activity To Fragment");
                //將數(shù)據(jù)傳遞到Fragment
                fragment.setArguments(bundle);
                FragmentManager fragmentManager = getSupportFragmentManager();
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                //FrameLayout用于動(dòng)態(tài)更新fragment
                fragmentTransaction.replace(R.id.frame_layout, fragment);
                fragmentTransaction.commit();
            }
        });
    }
}

??新建一個(gè)碎片ToFragment少梁，簡(jiǎn)單起見(jiàn)，就不給新建的碎片弄一個(gè)布局文件矫付，直接使用BlankFragment的布局文件凯沪，節(jié)省時(shí)間：

public class ToFragment extends Fragment {
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        //簡(jiǎn)單起見(jiàn)，此處直接使用BlankFragment的布局文件
        View view = inflater.inflate(R.layout.fragment_blank, container, false);

        TextView textView = view.findViewById(R.id.text_view);
        //得到從Activity傳來(lái)的數(shù)據(jù)
        Bundle bundle = this.getArguments();
        String message = null;
        if (bundle != null) {
            message = bundle.getString("data");
        }
        textView.setText(message);
        return view;
    }
}

??運(yùn)行程序后結(jié)果如下所示：

3. 在消息機(jī)制的Message中使用setData()傳遞數(shù)據(jù)時(shí)用到Bundle

??這個(gè)栗子的思路也很簡(jiǎn)單买优，點(diǎn)擊屏幕妨马，給Activity發(fā)送一個(gè)Message挺举，傳遞兩個(gè)參數(shù)，并通過(guò)Toast顯示出來(lái)烘跺，最后finish()掉這個(gè)Activity湘纵。
??新建一個(gè)Activity：

public class MainActivity extends AppCompatActivity {

    final static int FLAG = 1;

    @SuppressLint("HandlerLeak")
    public Handler mHandler = new Handler() {
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            switch (msg.what) {
                case FLAG:
                    //獲取Message傳遞過(guò)來(lái)的數(shù)據(jù)
                    String data1 = msg.getData().getString("text1");
                    String data2 = msg.getData().getString("text2");
                    init(data1, data2);
                    break;
                default:
                    break;
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new MyView(this, this));
    }

    public void init(String str1, String str2) {
        //將獲取的數(shù)據(jù)Toast出來(lái)
        Toast.makeText(MainActivity.this, str1 + '\n' + str2, Toast.LENGTH_SHORT).show();
        finish();
    }
}

??在建一個(gè)Java類(lèi)：

@SuppressLint("ViewConstructor")
public class MyView extends View {
    private MainActivity activity;

    public MyView(Context context, MainActivity activity) {
        super(context);
        this.activity = activity;
    }

    @SuppressLint("ClickableViewAccessibility")
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int)event.getX();
        int y = (int)event.getY();
        Rect rect = new Rect(0, 0, 320, 480);
        if (rect.contains(x, y)) {
            Message message = new Message();
            message.what = MainActivity.FLAG;
            //新建Bundle的實(shí)例
            Bundle bundle = new Bundle();
            //往Bundle中傳入數(shù)據(jù)
            bundle.putString("text1", "Trump want to ban TimTok");
            bundle.putString("text2", "Make America great again");
            //message利用bundle傳遞數(shù)據(jù)
            message.setData(bundle);
            //用activity中的handler發(fā)送消息
            activity.mHandler.sendMessage(message);
        }
        return super.onTouchEvent(event);
    }
}

??運(yùn)行程序，得到如下結(jié)果：

??點(diǎn)擊屏幕指定區(qū)域滤淳，得到如下結(jié)果：

六梧喷、小結(jié)

??到此，Bundle的分析基本就結(jié)束了脖咐，其實(shí)Bundle比較簡(jiǎn)單铺敌，只是一個(gè)數(shù)據(jù)容器，不像Activity等有復(fù)雜的生命周期屁擅。對(duì)于開(kāi)發(fā)者來(lái)說(shuō)偿凭，只需要了解Bundle的功能、使用場(chǎng)景并掌握常用的數(shù)據(jù)存取方法即可派歌。