Android“包裹”：Bundle

Bundle是谷歌封装好的“包裹”，官方的定义就是：A mapping from String keys to various Parcelable values。

1、Bundle介绍

Bundle位于android.os包中，用来携带数据，传递的数据可以是boolean、byte、int、long、float、double、string等基本类型或它们对应的数组，也可以是对象或对象数组。

用Bundle传递对象或对象数组时，必须实现Serializable 或Parcelable接口，关于Parcelable详见Android中的两种序列化：Parcelable和Serialable。

1.1、创建Bundle

使用Bundle直接new一个就可以了，构造一个空的Bundle对象。Bundle继承自BaseBundle，大部分功能，成员变量都封装在BaseBundle，继续往下看。

/**
     * Constructs a new, empty Bundle.
     */
    public Bundle() {
        super();
        mFlags = FLAG_HAS_FDS_KNOWN | FLAG_ALLOW_FDS;
    }

调用了BaseBundle构造函数，来声明一个Bundle对象。

/**
     * Constructs a new, empty Bundle.
     */
    BaseBundle() {
        this((ClassLoader) null, 0);
    }
    
    /**
     * Constructs a new, empty Bundle that uses a specific ClassLoader for
     * instantiating Parcelable and Serializable objects.
     *
     * @param loader An explicit ClassLoader to use when instantiating objects
     * inside of the Bundle.
     * @param capacity Initial size of the ArrayMap.
     */
    BaseBundle(@Nullable ClassLoader loader, int capacity) {
        mMap = capacity > 0 ?
                new ArrayMap<String, Object>(capacity) : new ArrayMap<String, Object>();
        mClassLoader = loader == null ? getClass().getClassLoader() : loader;
    }

看到有一个熟悉的mMap，没错，这个Map就是Bundle帮我们保存数据的映射ArrayMap。

mMap = capacity > 0 ? new ArrayMap<String, Object>(capacity) : new ArrayMap<String, Object>();

ArrayMap在android.util包中，继承了Map<K,V>接口，是谷歌提供给开发者的一种映射数据结构。虽然ArrayMap本身对键的类型没有限制，但是在Bundle中键值K已经被固定成String类型：

ArrayMap<String, Object> mMap;

1.2、put数据方法

上面简短的看了下源码，不难发现向Bundle中添加数据的时候，键只能是String类型。Bundle提供了很多put数据的方法：

`void`	`putAll(Bundle bundle)` Inserts all mappings from the given Bundle into this Bundle.
`void`	`putBinder(String key, IBinder value)` Inserts an `IBinder` value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putBundle(String key, Bundle value)` Inserts a Bundle value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putByte(String key, byte value)` Inserts a byte value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putByteArray(String key, byte[] value)` Inserts a byte array value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putChar(String key, char value)` Inserts a char value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putCharArray(String key, char[] value)` Inserts a char array value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putCharSequence(String key, CharSequence value)` Inserts a CharSequence value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putCharSequenceArray(String key, CharSequence[] value)` Inserts a CharSequence array value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putCharSequenceArrayList(String key, ArrayList<CharSequence> value)` Inserts an ArrayList value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putFloat(String key, float value)` Inserts a float value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putFloatArray(String key, float[] value)` Inserts a float array value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putIntegerArrayList(String key, ArrayList<Integer> value)` Inserts an ArrayList value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putParcelable(String key, Parcelable value)` Inserts a Parcelable value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putParcelableArray(String key, Parcelable[] value)` Inserts an array of Parcelable values into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putParcelableArrayList(String key, ArrayList<? extends Parcelable> value)` Inserts a List of Parcelable values into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putSerializable(String key, Serializable value)` Inserts a Serializable value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putShort(String key, short value)` Inserts a short value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putShortArray(String key, short[] value)` Inserts a short array value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putSize(String key, Size value)` Inserts a Size value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putSizeF(String key, SizeF value)` Inserts a SizeF value into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putSparseParcelableArray(String key, SparseArray<? extends Parcelable> value)` Inserts a SparceArray of Parcelable values into the mapping of this Bundle, replacing any existing value for the given key.
`void`	`putStringArrayList(String key, ArrayList<String> value)` Inserts an ArrayList value into the mapping of this Bundle, replacing any existing value for the given key.

2、Android有哪些封装了Bundle？

框架中很多地方用到Bundle，比如：

①Message：信使Message：子线程数据携带到主线程

Message msg = Message.obtain();
    Bundle bundle = new Bundle();
    msg.setData(bundle);

②Intent

Intent intent = new Intent();
    Bundle bundle = new Bundle();
    intent.putExtras(bundle);

... ...

Android“包裹”：Bundle