android開發之Parcelable使用詳解
阿新 • • 發佈:2019-02-19
想要在兩個activity之間傳遞物件,那麼這個物件必須序列化,android中序列化一個物件有兩種方式,一種是實現Serializable介面,這個非常簡單,只需要宣告一下就可以了,不痛不癢。但是android中還有一種特有的序列化方法,那就是實現Parcelable介面,使用這種方式來序列化的效率要高於實現Serializable介面。不過Serializable介面實在是太方便了,因此在某些情況下實現這個介面還是非常不錯的選擇。
使用Parcelable步驟:
1.實現Parcelable介面
2.實現介面中的兩個方法
public int describeContents();
public void writeToParcel(Parcel dest, int flags);
第一個方法是內容介面描述,預設返回0就可以了
第二個方法是將我們的物件序列化一個Parcel物件,也就是將我們的物件存入Parcel中
3.例項化靜態內部物件CREATOR實現介面Parcelable.Creator,例項化CREATOR時要實現其中的兩個方法,其中createFromParcel
的功能就是從Parcel中讀取我們的物件。
也就是說我們先利用writeToParcel
方法寫入物件,再利用createFromParcel
方法讀取物件,因此這兩個方法中的讀寫順序必須一致,否則會出現資料紊亂,一會我會舉例子。
看一個程式碼示例:
public class Person implements Parcelable{
private String username;
private String nickname;
private int age;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getNickname () {
return nickname;
}
public void setNickname(String nickname) {
this.nickname = nickname;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Person(String username, String nickname, int age) {
super();
this.username = username;
this.nickname = nickname;
this.age = age;
}
public Person() {
super();
}
/**
* 這裡的讀的順序必須與writeToParcel(Parcel dest, int flags)方法中
* 寫的順序一致,否則資料會有差錯,比如你的讀取順序如果是:
* nickname = source.readString();
* username=source.readString();
* age = source.readInt();
* 即調換了username和nickname的讀取順序,那麼你會發現你拿到的username是nickname的資料,
* 而你拿到的nickname是username的資料
* @param source
*/
public Person(Parcel source) {
username = source.readString();
nickname=source.readString();
age = source.readInt();
}
/**
* 這裡預設返回0即可
*/
@Override
public int describeContents() {
return 0;
}
/**
* 把值寫入Parcel中
*/
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(username);
dest.writeString(nickname);
dest.writeInt(age);
}
public static final Creator<Person> CREATOR = new Creator<Person>() {
/**
* 供外部類反序列化本類陣列使用
*/
@Override
public Person[] newArray(int size) {
return new Person[size];
}
/**
* 從Parcel中讀取資料
*/
@Override
public Person createFromParcel(Parcel source) {
return new Person(source);
}
};
}
最後貼上Parcelable原始碼,Google已經給了一個示例了:
/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.os;
/**
* Interface for classes whose instances can be written to
* and restored from a {@link Parcel}. Classes implementing the Parcelable
* interface must also have a static field called <code>CREATOR</code>, which
* is an object implementing the {@link Parcelable.Creator Parcelable.Creator}
* interface.
*
* <p>A typical implementation of Parcelable is:</p>
*
* <pre>
* public class MyParcelable implements Parcelable {
* private int mData;
*
* public int describeContents() {
* return 0;
* }
*
* public void writeToParcel(Parcel out, int flags) {
* out.writeInt(mData);
* }
*
* public static final Parcelable.Creator<MyParcelable> CREATOR
* = new Parcelable.Creator<MyParcelable>() {
* public MyParcelable createFromParcel(Parcel in) {
* return new MyParcelable(in);
* }
*
* public MyParcelable[] newArray(int size) {
* return new MyParcelable[size];
* }
* };
*
* private MyParcelable(Parcel in) {
* mData = in.readInt();
* }
* }</pre>
*/
public interface Parcelable {
/**
* Flag for use with {@link #writeToParcel}: the object being written
* is a return value, that is the result of a function such as
* "<code>Parcelable someFunction()</code>",
* "<code>void someFunction(out Parcelable)</code>", or
* "<code>void someFunction(inout Parcelable)</code>". Some implementations
* may want to release resources at this point.
*/
public static final int PARCELABLE_WRITE_RETURN_VALUE = 0x0001;
/**
* Bit masks for use with {@link #describeContents}: each bit represents a
* kind of object considered to have potential special significance when
* marshalled.
*/
public static final int CONTENTS_FILE_DESCRIPTOR = 0x0001;
/**
* Describe the kinds of special objects contained in this Parcelable's
* marshalled representation.
*
* @return a bitmask indicating the set of special object types marshalled
* by the Parcelable.
*/
public int describeContents();
/**
* Flatten this object in to a Parcel.
*
* @param dest The Parcel in which the object should be written.
* @param flags Additional flags about how the object should be written.
* May be 0 or {@link #PARCELABLE_WRITE_RETURN_VALUE}.
*/
public void writeToParcel(Parcel dest, int flags);
/**
* Interface that must be implemented and provided as a public CREATOR
* field that generates instances of your Parcelable class from a Parcel.
*/
public interface Creator<T> {
/**
* Create a new instance of the Parcelable class, instantiating it
* from the given Parcel whose data had previously been written by
* {@link Parcelable#writeToParcel Parcelable.writeToParcel()}.
*
* @param source The Parcel to read the object's data from.
* @return Returns a new instance of the Parcelable class.
*/
public T createFromParcel(Parcel source);
/**
* Create a new array of the Parcelable class.
*
* @param size Size of the array.
* @return Returns an array of the Parcelable class, with every entry
* initialized to null.
*/
public T[] newArray(int size);
}
/**
* Specialization of {@link Creator} that allows you to receive the
* ClassLoader the object is being created in.
*/
public interface ClassLoaderCreator<T> extends Creator<T> {
/**
* Create a new instance of the Parcelable class, instantiating it
* from the given Parcel whose data had previously been written by
* {@link Parcelable#writeToParcel Parcelable.writeToParcel()} and
* using the given ClassLoader.
*
* @param source The Parcel to read the object's data from.
* @param loader The ClassLoader that this object is being created in.
* @return Returns a new instance of the Parcelable class.
*/
public T createFromParcel(Parcel source, ClassLoader loader);
}
}