Android中的Parcel机制 实现Bundle传递对象
Android中的Parcel机制
实现了Bundle传递对象
使用Bundle传递对象,首先要将其序列化,但是,在Android中要使用这种传递对象的方式需要用到Android Parcel机制,即,Android实现的轻量级的高效的对象序列化和反序列化机制。
JAVA中的Serialize机制,译成串行化、序列化……,其作用是能将数据对象存入字节流当中,在需要时重新生成对象。主要应用是利用外部存储设备保存对象状态,以及通过网络传输对象等。
Android中的新的序列化机制
在Android系统中,定位为针对内存受限的设备,因此对性能要求更高,另外系统中采用了新的IPC(进程间通信)机制,必然要求使用性能更出色的对象传输方式。在这样的环境下,
Parcel被设计出来,其定位就是轻量级的高效的对象序列化和反序列化机制。
Android中序列化有以下几个特征:
1. 整个读写全是在内存中进行,所以效率比JAVA序列化中使用外部存储器会高很多;
2. 读写时是4字节对齐的
3. 如果预分配的空间不够时,会一次多分配50%;
4. 对于普通数据,使用的是mData内存地址,对于IBinder类型的数据以及FileDescriptor使用的是mObjects内存地址。后者是通过flatten_binder()和unflatten_binder()实现的,目的是反序列化时读出的对象就是原对象而不用重新new一个新对象。
package com.parcel.main; import android.app.Activity; import android.content.Intent; import android.graphics.Color; import android.graphics.drawable.Drawable; import android.os.Bundle; import android.view.MotionEvent; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView; public class MyTestParcelActivity extends Activity { public final static int Sub_Main = 1; public final static int Sub_2_Main = 2; private Button setSubMain; private Button setSub2Main; private TextView mTextView; private Drawable defDrawable; private MyParcel mMyParcel = new MyParcel(); private BinderMyParcel mBinderMyParcel = new BinderMyParcel(); /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); initComponent(); } private void initComponent() { setSubMain = (Button) findViewById(R.id.btn01); if (setSubMain != null) { setSubMain.setOnClickListener(setSubMainXML); } setSub2Main = (Button) findViewById(R.id.btn04); if (setSub2Main != null) { setSub2Main.setOnClickListener(setSub2MainXML); } mTextView = (TextView) findViewById(R.id.main_tv); defDrawable = mTextView.getBackground(); } private View.OnClickListener setSubMainXML = new OnClickListener() { @Override public void onClick(View v) { Intent mIntent = new Intent(); if (mMyParcel != null) { mMyParcel.setColor(Color.RED); mIntent.putExtra("MyColor", mMyParcel); } mIntent.setClass(MyTestParcelActivity.this, SubMyTestParcelActivity.class); mTextView.setBackgroundDrawable(defDrawable); startActivityForResult(mIntent, Sub_Main); } }; private View.OnClickListener setSub2MainXML = new OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(); if (mBinderMyParcel != null) { mBinderMyParcel.setColor(Color.MAGENTA); intent.putExtra("BinderMyColor", mBinderMyParcel); } intent.setClass(MyTestParcelActivity.this, Sub2MyTestParcelActivity.class); mTextView.setBackgroundDrawable(defDrawable); startActivityForResult(intent, Sub_2_Main); } }; @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { super.onActivityResult(requestCode, resultCode, data); if (resultCode == RESULT_OK) { if (requestCode == Sub_Main) { if (data.hasExtra("MyColor")) { /** * color=data.getParcelableExtra("MyColor"), * 这说明反序列化后是一个新的MyColor对象 * * 如果数据本身是IBinder类型,那么反序列化的结果就是原对象,而不是新建的对象 */ mMyParcel = data.getParcelableExtra("MyColor"); ((TextView) findViewById(R.id.main_tv)) .setTextColor(mMyParcel.getColor()); } } else if (requestCode == Sub_2_Main) { if (data.hasExtra("BinderMyColor")) { ((TextView) findViewById(R.id.main_tv)) .setBackgroundColor(mBinderMyParcel.getColor()); } } } } @Override public boolean onTouchEvent(MotionEvent event) { return super.onTouchEvent(event); } }
使用非binder类型代码
package com.parcel.main; import android.app.Activity; import android.content.Intent; import android.graphics.Color; import android.graphics.drawable.Drawable; import android.os.Bundle; import android.view.MotionEvent; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView; public class SubMyTestParcelActivity extends Activity implements OnClickListener { private Button setSub2XML; private TextView mTextView; private MyParcel myColor; private Drawable defDrawable; /** Called when the activity is first created. */ @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.submain); setSub2XML = (Button) findViewById(R.id.btn02); setSub2XML.setOnClickListener(this); mTextView = (TextView)findViewById(R.id.sub_tv); defDrawable = mTextView.getBackground(); Intent intent = getIntent(); if (intent != null) { if (intent.hasExtra("MyColor")) { myColor = intent.getParcelableExtra("MyColor"); mTextView.setBackgroundColor(myColor.getColor()); } } } @Override protected void onStart() { super.onStart(); } @Override protected void onRestart() { super.onRestart(); } @Override protected void onResume() { super.onResume(); } @Override protected void onPause() { super.onPause(); } @Override protected void onStop() { super.onStop(); } @Override protected void onDestroy() { super.onDestroy(); } @Override public boolean onTouchEvent(MotionEvent event) { return super.onTouchEvent(event); } @Override public void onClick(View v) { switch (v.getId()) { case R.id.btn02: Intent mIntent = new Intent(getApplicationContext(), Sub2MyTestParcelActivity.class); if (myColor != null) { myColor.setColor(Color.GREEN); mIntent.putExtra("MyColor", myColor); } mTextView.setBackgroundDrawable(defDrawable); setResult(RESULT_OK, mIntent); finish(); break; default: break; } } }
使用binder类型代码
package com.parcel.main; import android.app.Activity; import android.content.Intent; import android.graphics.Color; import android.graphics.drawable.Drawable; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView; public class Sub2MyTestParcelActivity extends Activity implements OnClickListener { private Button setMainXML; private TextView mTextView; private BinderMyParcel myColor; private Drawable defDrawable; /** Called when the activity is first created. */ @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.sub2main); setMainXML = (Button) findViewById(R.id.btn03); setMainXML.setOnClickListener(this); mTextView = (TextView) findViewById(R.id.sub_tv); defDrawable = mTextView.getBackground(); Intent intent = getIntent(); if (intent != null) { if (intent.hasExtra("BinderMyColor")) { myColor = intent.getParcelableExtra("BinderMyColor"); mTextView.setBackgroundColor(myColor.getColor()); } } } @Override public void onClick(View v) { switch (v.getId()) { case R.id.btn03: Intent mIntent = new Intent(getApplicationContext(), MyTestParcelActivity.class); if (myColor != null) { myColor.setColor(Color.WHITE); mIntent.putExtra("BinderMyColor", myColor); } mTextView.setBackgroundDrawable(defDrawable); setResult(RESULT_OK, mIntent); finish(); break; default: break; } } }
非Binder类型的Parcel,实现Parcelable接口即可:
package com.parcel.main; import android.graphics.Color; import android.os.Parcel; import android.os.Parcelable; public class MyParcel implements Parcelable { private int color = Color.BLACK; public int getColor() { return color; } public void setColor(int color) { this.color = color; } public MyParcel() { color = Color.BLACK; } public MyParcel(Parcel in) { color = in.readInt(); } @Override public int describeContents() { return 0; } @Override public void writeToParcel(Parcel dest, int flags) { dest.writeInt(color); } public static final Parcelable.Creator<MyParcel> CREATOR = new Parcelable.Creator<MyParcel>() { public MyParcel createFromParcel(Parcel in) { return new MyParcel(in); } public MyParcel[] newArray(int size) { return new MyParcel[size]; } }; }
对于Binder类型,首先要实现一个Binder接口(其,最主要的区别在于反序列化仍然是原来的对象,而非Binder类型的反序列化并不是原来的对象,所以在MainActivity中的onActivityResult方法中会出现mMyParcel = data.getParcelableExtra("MyColor")的写法):
package com.parcel.main; import android.os.Binder; public class BinderData extends Binder { public int color; }
其次再实现Parcelable接口:
package com.parcel.main; import android.graphics.Color; import android.os.Parcel; import android.os.Parcelable; public class BinderMyParcel implements Parcelable { private BinderData data = new BinderData(); public BinderMyParcel() { data.color = Color.BLUE; } public BinderMyParcel(Parcel in) { data = (BinderData) in.readValue(BinderData.class.getClassLoader()); } public void setColor(int color) { data.color = color; } public int getColor() { return data.color; } @Override public int describeContents() { return 0; } @Override public void writeToParcel(Parcel dest, int flags) { dest.writeValue(data); } public static final Parcelable.Creator<BinderMyParcel> CREATOR = new Creator<BinderMyParcel>() { @Override public BinderMyParcel[] newArray(int size) { return new BinderMyParcel[size]; } @Override public BinderMyParcel createFromParcel(Parcel source) { return new BinderMyParcel(source); } }; }
三个XML:
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <TextView android:id="@+id/main_tv" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/main_activity" /> <LinearLayout android:orientation="horizontal" android:layout_width="wrap_content" android:layout_height="wrap_content"> <Button android:text="SetSubMainXML" android:id="@+id/btn01" android:layout_width="wrap_content" android:layout_height="wrap_content" /> <Button android:id="@+id/btn04" android:layout_height="wrap_content" android:layout_width="wrap_content" android:text="SetSub2MainXML" /> </LinearLayout> </LinearLayout>
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <TextView android:id="@+id/sub_tv" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/sub_activity" /> <Button android:text="setMainXML" android:id="@+id/btn02" android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout>
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <TextView android:id="@+id/sub_tv" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/sub2_activity" /> <Button android:text="setMainXML" android:id="@+id/btn03" android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout>