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Android中的Parcel机制 实现Bundle传送对象

分类: IT文章 • 2023-12-15 20:52:43
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);
	}

}
  
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;
		}
	}

}
  
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>
 

 

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