如何將 Parcelable 保存到本地文件裏

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Seriaizeable 可以序列化長期保存到本地文件裏，那麼Parcelable 可不可以呢？

在閱讀了Parcel的源碼之後，發現了很多的 writexxx 和 readxxx 方法，這個後續再做分析，這篇主要描述一下另外兩個方法marshall 和 unmarshall, 這兩個函數是相互對應的.

marshall: Parcel 將自身所保存的所有數據以 byte 數組的形式返回

/**
 * Returns the raw bytes of the parcel.
 *
 * <p class="note">The data you retrieve here <strong>must not</strong>
 * be placed in any kind of persistent storage (on local disk, across
 * a network, etc).  For that, you should use standard serialization
 * or another kind of general serialization mechanism.  The Parcel
 * marshalled representation is highly optimized for local IPC, and as
 * such does not attempt to maintain compatibility with data created
 * in different versions of the platform.
 */
public final byte[] marshall() {
    return nativeMarshall(mNativePtr);
}

unmarshall: 從 byte 數組裏獲取數據，存入自身 Parcel

/**
 * Set the bytes in data to be the raw bytes of this Parcel.
 */
public final void unmarshall(byte[] data, int offset, int length) {
    nativeUnmarshall(mNativePtr, data, offset, length);
}

既然Parcel 可以轉化成 byte[]，也可以從byte[] 裏獲取數據，那麼我們就可以這樣做：

import android.os.Parcel;
import android.os.Parcelable;
import android.util.Log;

public class ParcelableUtil {
    public static byte[] marshall(Parcelable parceable) {
        Parcel parcel = Parcel.obtain();
        parcel.setDataPosition(0);
        parceable.writeToParcel(parcel, 0);
        byte[] bytes = parcel.marshall();

        Log.d("ParcelableTest", "bytes = " + String.valueOf(bytes) + "parcel" + parcel.toString());
        parcel.recycle();
        return bytes;
    }

    public static Parcel unmarshall(byte[] bytes) {
        Parcel parcel = Parcel.obtain();
        parcel.unmarshall(bytes, 0, bytes.length);
        parcel.setDataPosition(0);
        return parcel;
    }

}

// MainActivity.java
private void testParcelableMarshall() {
    ParcelableTest parcelableTest = new ParcelableTest(1, 2, 3, "HelloWorld!");
    parcelableTest.toString();

    byte[] bytes = ParcelableUtil.marshall(parcelableTest);

    SharedPreferences.Editor parcelableEditor = getSharedPreferences("parcelable", 0).edit();
    //parcelableEditor.putString("parcelable", new String(bytes));
    parcelableEditor.putString("parcelable", Base64.encodeToString(bytes, 0));
    parcelableEditor.commit();


    SharedPreferences parcelable = getSharedPreferences("parcelable", 0);
    //Parcel parcel = ParcelableUtil.unmarshall(parcelable.getString("parcelable", "default").getBytes());
    Parcel parcel = ParcelableUtil.unmarshall(Base64.decode(parcelable.getString("parcelable", "default"), 0));

    Log.d("ParcelableTest", String.valueOf(bytes).toString() + "bytes = " + parcelable.getString("parcelable", "default").toString() + "parcel" + parcel.toString());
    ParcelableTest parcelableTest1 = null;
    parcelableTest1 = ParcelableTest.CREATOR.createFromParcel(parcel);
    parcelableTest1.toString();
}

在調用 testParcelableMarshall() 之後結果如下：

D/ParcelableTest( 7923): t1 = 1 t2 = 2 t3 = 3 a = HelloWorld!
D/ParcelableTest( 7923): Call writeToParcel
D/ParcelableTest( 7923): bytes = [[e-mail]@b373bee
D/ParcelableTest( 7923): [B@3043c569bytes = AQAAAAIAAAADAAAACwAAAEgAZQBsAGwAbwBXAG8AcgBsAGQAIQAAAA==
D/ParcelableTest( 7923): parcelandroid.os.Parcel@b373bee
D/ParcelableTest( 7923): Call createFromParcel
D/ParcelableTest( 7923): Call ParcelableTest
D/ParcelableTest( 7923): t1 = 1 t2 = 2 t3 = 3 a = HelloWorld!

事實證明，Parcelable 成功的保存到了持久化的文件裏。

如圖所示： 如圖所示