可定制的Cursor--MatrixCursor
ContentProvider对外共享数据的时候的query()方法是需要一个cursor的。
但是如果没有数据库，需要对外共享数据使用ContentProvider的时候怎么办？
而有一些其他方法操作也都是需要cursor的。
此时就需要MatrixCursor了。相当有趣，它相当于为你模拟了一个表。代码如下：
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
String[] tableCursor = new String[] { "name", "job", "salary" };
MatrixCursor cursor = new MatrixCursor(tableCursor);
cursor.addRow(new Object[] { "1111", "1111", "1111" });
return cursor;
}
以上来自：http://www.cnblogs.com/topcoderliu/archive/2011/04/26/2029576.html
MatrixCursor还可以对已经查询完成得到的Cursor中的数据进行在二次处理，完成对Cursor的数据过滤，代码如下：
MatrixCursor还可以对已经查询完成得到的Cursor中的数据进行在二次处理，完成对Cursor的数据过滤，代码如下：
private Cursor cursorFilter(Cursor cursor){
MatrixCursor matrixcursor=null;
if(cursor!=null&&cursor.getCount()>0){
matrixcursor = new MatrixCursor(columnNames);
while(cursor.moveToNext()){
for(int i=0;i<4;i++){
columns[i]=cursor.getString(i);
}
if(filterbyrule(columns[3],columns[2])){
matrixcursor.addRow(columns);
}
}
}
return matrixcursor;
}Cursor 位于 android.database.Cursor类，它的设计是基于数据库服务产生的。
它有几个己知的子类，分别为：
- AbstractCursor
- AbstractWindowedCursor
- CrossProcessCursor
- CursorWrapper
- MatrixCursor
- MergeCursor
- MockCursor
- SQLiteCursor
MatrixCursor子类的源码如下：
package android.database;
import java.util.ArrayList;
/**
* A mutable cursor implementation backed by an array of {@code Object}s. Use
* {@link #newRow()} to add rows. Automatically expands internal capacity
* as needed.
* 一个通过Object数组实现的容易改变的cursor，通过newRow（）增加记录。
* 它具有根据需要自动扩容的能力
*/
public class MatrixCursor extends AbstractCursor {
private final String[] columnNames;
private Object[] data;
private int rowCount = 0;
private final int columnCount;
/**
* Constructs a new cursor with the given initial capacity.
*
* @param columnNames names of the columns, the ordering of which
* determines column ordering elsewhere in this cursor
* @param initialCapacity in rows
*/
public MatrixCursor(String[] columnNames, int initialCapacity) {
this.columnNames = columnNames;
this.columnCount = columnNames.length;
if (initialCapacity < 1) {
initialCapacity = 1;
}
this.data = new Object[columnCount * initialCapacity];
}
/**
* Constructs a new cursor.
*
* @param columnNames names of the columns, the ordering of which
* determines column ordering elsewhere in this cursor
*/
public MatrixCursor(String[] columnNames) {
this(columnNames, 16);
}
/**
* Gets value at the given column for the current row.
*/
private Object get(int column) {
if (column < 0 || column >= columnCount) {
throw new CursorIndexOutOfBoundsException("Requested column: "
+ column + ", # of columns: " + columnCount);
}
if (mPos < 0) {
throw new CursorIndexOutOfBoundsException("Before first row.");
}
if (mPos >= rowCount) {
throw new CursorIndexOutOfBoundsException("After last row.");
}
return data[mPos * columnCount + column];
}
/**
* Adds a new row to the end and returns a builder for that row. Not safe
* for concurrent use.
*
* @return builder which can be used to set the column values for the new
* row
*/
public RowBuilder newRow() {
rowCount++;
int endIndex = rowCount * columnCount;
ensureCapacity(endIndex);
int start = endIndex - columnCount;
return new RowBuilder(start, endIndex);
}
/**
* Adds a new row to the end with the given column values. Not safe
* for concurrent use.
*
* @throws IllegalArgumentException if {@code columnValues.length !=
* columnNames.length}
* @param columnValues in the same order as the the column names specified
* at cursor construction time
*/
public void addRow(Object[] columnValues) {
if (columnValues.length != columnCount) {
throw new IllegalArgumentException("columnNames.length = "
+ columnCount + ", columnValues.length = "
+ columnValues.length);
}
int start = rowCount++ * columnCount;
ensureCapacity(start + columnCount);
System.arraycopy(columnValues, 0, data, start, columnCount);
}
/**
* Adds a new row to the end with the given column values. Not safe
* for concurrent use.
*
* @throws IllegalArgumentException if {@code columnValues.size() !=
* columnNames.length}
* @param columnValues in the same order as the the column names specified
* at cursor construction time
*/
public void addRow(Iterable columnValues) {
int start = rowCount * columnCount;
int end = start + columnCount;
ensureCapacity(end);
if (columnValues instanceof ArrayList) {
addRow((ArrayList) columnValues, start);
return;
}
int current = start;
Object[] localData = data;
for (Object columnValue : columnValues) {
if (current == end) {
// TODO: null out row?
throw new IllegalArgumentException(
"columnValues.size() > columnNames.length");
}
localData[current++] = columnValue;
}
if (current != end) {
// TODO: null out row?
throw new IllegalArgumentException(
"columnValues.size() < columnNames.length");
}
// Increase row count here in case we encounter an exception.
rowCount++;
}
/** Optimization for {@link ArrayList}. */
private void addRow(ArrayList columnValues, int start) {
int size = columnValues.size();
if (size != columnCount) {
throw new IllegalArgumentException("columnNames.length = "
+ columnCount + ", columnValues.size() = " + size);
}
rowCount++;
Object[] localData = data;
for (int i = 0; i < size; i++) {
localData[start + i] = columnValues.get(i);
}
}
/** Ensures that this cursor has enough capacity. */
private void ensureCapacity(int size) {
if (size > data.length) {
Object[] oldData = this.data;
int newSize = data.length * 2;
if (newSize < size) {
newSize = size;
}
this.data = new Object[newSize];
System.arraycopy(oldData, 0, this.data, 0, oldData.length);
}
}
/**
* Builds a row, starting from the left-most column and adding one column
* value at a time. Follows the same ordering as the column names specified
* at cursor construction time.
*/
public class RowBuilder {
private int index;
private final int endIndex;
RowBuilder(int index, int endIndex) {
this.index = index;
this.endIndex = endIndex;
}
/**
* Sets the next column value in this row.
*
* @throws CursorIndexOutOfBoundsException if you try to add too many
* values
* @return this builder to support chaining
*/
public RowBuilder add(Object columnValue) {
if (index == endIndex) {
throw new CursorIndexOutOfBoundsException(
"No more columns left.");
}
data[index++] = columnValue;
return this;
}
}
// AbstractCursor implementation.
@Override
public int getCount() {
return rowCount;
}
@Override
public String[] getColumnNames() {
return columnNames;
}
@Override
public String getString(int column) {
Object value = get(column);
if (value == null) return null;
return value.toString();
}
@Override
public short getShort(int column) {
Object value = get(column);
if (value == null) return 0;
if (value instanceof Number) return ((Number) value).shortValue();
return Short.parseShort(value.toString());
}
@Override
public int getInt(int column) {
Object value = get(column);
if (value == null) return 0;
if (value instanceof Number) return ((Number) value).intValue();
return Integer.parseInt(value.toString());
}
@Override
public long getLong(int column) {
Object value = get(column);
if (value == null) return 0;
if (value instanceof Number) return ((Number) value).longValue();
return Long.parseLong(value.toString());
}
@Override
public float getFloat(int column) {
Object value = get(column);
if (value == null) return 0.0f;
if (value instanceof Number) return ((Number) value).floatValue();
return Float.parseFloat(value.toString());
}
@Override
public double getDouble(int column) {
Object value = get(column);
if (value == null) return 0.0d;
if (value instanceof Number) return ((Number) value).doubleValue();
return Double.parseDouble(value.toString());
}
@Override
public boolean isNull(int column) {
return get(column) == null;
}
}