MediaScannerReceiver

源码android/packages/apps/providers/media/src/com/android/providers/media/MediaScannerReceiver.java

package com.android.providers.media;

import android.content.Context;
import android.content.Intent;
import android.content.BroadcastReceiver;
import android.net.Uri;
import android.os.Environment;
import android.os.Bundle;

import java.io.File;

public class MediaScannerReceiver extends BroadcastReceiver
{
private final static String TAG = "MediaScannerReceiver";

@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
Uri uri = intent.getData();
String externalStoragePath = Environment.getExternalStorageDirectory().getPath();

if (action.equals(Intent.ACTION_BOOT_COMPLETED)) {
// scan internal storage
scan(context, MediaProvider.INTERNAL_VOLUME);

// scan external storage if it is mounted
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state) ||
Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
scan(context, MediaProvider.EXTERNAL_VOLUME);
}
} else {
if (uri.getScheme().equals("file")) {
// handle intents related to external storage
String path = uri.getPath();
if (action.equals(Intent.ACTION_MEDIA_MOUNTED) &&
externalStoragePath.equals(path)) {
scan(context, MediaProvider.EXTERNAL_VOLUME);
} else if (action.equals(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE) &&
path != null && path.startsWith(externalStoragePath + "/")) {
scanFile(context, path);
}
}
}
}

private void scan(Context context, String volume) {
Bundle args = new Bundle();
args.putString("volume", volume);
context.startService(
new Intent(context, MediaScannerService.class).putExtras(args));
}

private void scanFile(Context context, String path) {
Bundle args = new Bundle();
args.putString("filepath", path);
context.startService(
new Intent(context, MediaScannerService.class).putExtras(args));
}
}

从上面的源码可以总结以下几点：
1，action.equals(Intent.ACTION_BOOT_COMPLETED)
每当机器boot完之后就会发出Intent.ACTION_BOOT_COMPLETED，而在MediaScannerReceiver 接到该Action之后就对Internal 和External(若Sdcard挂载了)扫描，将其数据扫描到对应的数据库。所以你在开发的时候，每次开模拟器或手机你注意Logcat信息，就可以发现：scanner Internal Volumn...等等相关信息

2，uri.getScheme().equals("file")
除了接受机器boot完的Action要去扫描，还接受了以file中的两种扫描：扫描External和扫描一个文件：
1)
action.equals(Intent.ACTION_MEDIA_MOUNTED) &&
externalStoragePath.equals(path)[/color])
scan(context, MediaProvider.EXTERNAL_VOLUME);
2)
Intent.ACTION_MEDIA_SCANNER_SCAN_FILE) &&
path != null[/color] && path.startsWith(externalStoragePath + "/")) {
scanFile(context, path)

我们可以找到android自带ap的里运用了这种，就是Deve Tool里的Media Scanner,其扫描Sdcard:
其源码：apps›Development›src›com›android›development›MediaScannerActivity.java

package com.android.development;import android.app.Activity;import android.content.Context;import android.content.Intent;import android.content.IntentFilter;import android.content.BroadcastReceiver;import android.net.Uri;import android.os.Environment;import android.widget.TextView;public class MediaScannerActivity extends Activity{    public MediaScannerActivity() {    }    /** Called when the activity is first created or resumed. */    @Override    public void onResume() {        super.onResume();        setContentView(R.layout.media_scanner_activity);        [color=red]IntentFilter intentFilter = new IntentFilter(Intent.ACTION_MEDIA_SCANNER_STARTED);        intentFilter.addAction(Intent.ACTION_MEDIA_SCANNER_FINISHED);        intentFilter.addDataScheme("file");        registerReceiver(mReceiver, intentFilter)[/color];        sendBroadcast(new Intent(Intent.ACTION_MEDIA_MOUNTED, Uri.parse("file://"                + Environment.getExternalStorageDirectory())));        mTitle = (TextView) findViewById(R.id.title);        mTitle.setText("Sent ACTION_MEDIA_MOUNTED to trigger the Media Scanner.");    }    /** Called when the activity going into the background or being destroyed. */    @Override    public void onPause() {        super.onPause();        unregisterReceiver(mReceiver);    }    private final BroadcastReceiver mReceiver = new BroadcastReceiver() {        @Override        public void onReceive(Context context, Intent intent) {            if (intent.getAction().equals(Intent.ACTION_MEDIA_SCANNER_STARTED)) {                mTitle.setText("Media Scanner started scanning " + intent.getData().getPath());            }            else if (intent.getAction().equals(Intent.ACTION_MEDIA_SCANNER_FINISHED)) {                mTitle.setText("Media Scanner finished scanning " + intent.getData().getPath());            }        }    };    private TextView mTitle;}

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