file1.txt

fragment传递数据到activity:fragment定义接口 activity去实现这个接口
acitivity 传递数据到fragment:1.fragment中定义公共方法，activity中获取fragment实例
   	 	然后调用公共方法。
		  					2.fragment setArguments(Bundle)
							
							
isTaskRoot和moveTaskToBack方法简介


/* Checks if external storage is available for read and write */
public boolean isExternalStorageWritable() {
    String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state)) {
        return true;
    }
    return false;
}

/* Checks if external storage is available to at least read */
public boolean isExternalStorageReadable() {
    String state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state) ||
        Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        return true;
    }
    return false;
}


契约类是用于定义 URI、表格和列名称的常数的容器。

public final class FeedReaderContract {
    // To prevent someone from accidentally instantiating the contract class,
    // make the constructor private.
    private FeedReaderContract() {}

    /* Inner class that defines the table contents */
    public static class FeedEntry implements BaseColumns {
        public static final String TABLE_NAME = "entry";
        public static final String COLUMN_NAME_TITLE = "title";
        public static final String COLUMN_NAME_SUBTITLE = "subtitle";
    }
}

//表的创建和删除语句
private static final String TEXT_TYPE = " TEXT";
private static final String COMMA_SEP = ",";
private static final String SQL_CREATE_ENTRIES =
    "CREATE TABLE " + FeedEntry.TABLE_NAME + " (" +
    FeedEntry._ID + " INTEGER PRIMARY KEY," +
    FeedEntry.COLUMN_NAME_TITLE + TEXT_TYPE + COMMA_SEP +
    FeedEntry.COLUMN_NAME_SUBTITLE + TEXT_TYPE + " )";

private static final String SQL_DELETE_ENTRIES =
    "DROP TABLE IF EXISTS " + FeedEntry.TABLE_NAME;
	
	

//数据库操作费事，所以放在子线程中操作 子线程操作需要保证单一的数据库实例
	private static MyDBService instance;
	private MyDatabaseHelper myDatabaseHelper;

	private MyDBService(Context context){
	    myDatabaseHelper = new MyDatabaseHelper(mContext);
	}

	public static synchronized MyDBService getInstance(Context context){
	    if(instance == null){
	        instance = new MyDBService(context);
	    }
	    return instance;
	}

	public synchronized SQLiteDatabase getDataBase() {
	    if(myDatabaseHelper != null){
	        db = myDatabaseHelper.getWritableDatabase();
	    }
	    return db;
	}
	
	
	Fragment中启动，Activity中接收结果：使用getActivity().startActivityForResult()
	Fragment中启动，Fragment中接收结果：使用startActivityForResult()，且在Activity的onActivityResult()中调用super.onActivityResult()