Android 浅谈MatrixCursor

如果想得到一个Cursor, 而此时又没有数据库返回一个Cursor，此时可以通过MatrixCursor来返回一个Cursor

具体使用方法，请见下文：

假如有一个如下的数据库表结构

_id	name	price
R.drawable.ic_launcher	zhangsan	39
R.drawable.ic_launcher	lisi	40
R.drawable.ic_launcher	wangwu	41
R.drawable.ic_launcher	zhaoliu	42

现在咱们就通过MatrixCursor这个东西，来虚构出一张上面那样的表结构，下面通过一个例子，就可以完全理解MatrixCursor这个东西啦！！

(原文链接：http://blog.csdn.net/yelangjueqi/article/details/21232659  欢迎转载，尊重他人劳动成果，转载时请注明出处！！)

 

通过一个例子来分析一下：

 

package com.test.matrixcursor;

import android.app.ListActivity;
import android.database.MatrixCursor;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;
import android.view.View;
import android.widget.ListView;
import android.widget.Toast;

public class MainActivity extends ListActivity {
     private static final String[] COLUMN_NAME = { "_id", "name", "price" };
     private MatrixCursor matrixCursor;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
           createList();
           //createList2();
     }

     private void createList() {
          matrixCursor = new MatrixCursor(COLUMN_NAME, 1);
          startManagingCursor(matrixCursor);

          matrixCursor.addRow(new Object[] { R.drawable.ic_launcher, "zhangsan",
                    39 });
          matrixCursor
                    .addRow(new Object[] { R.drawable.ic_launcher, "lisi", 40 });
          matrixCursor
                    .addRow(new Object[] { R.drawable.ic_launcher, "wangwu", 41 });

          matrixCursor.addRow(new Object[] { R.drawable.ic_launcher, "zhaoliu",
                    42 });
          matrixCursor
                    .addRow(new Object[] { R.drawable.ic_launcher, "sunqi", 43 });

          setListAdapter(new SimpleCursorAdapter(this, R.layout.activity_main,
                    matrixCursor, COLUMN_NAME, new int[] { R.id.icon, R.id.name,
                              R.id.price }));
     }

     private void createList2() {
          matrixCursor = new MatrixCursor(COLUMN_NAME, 1);
          startManagingCursor(matrixCursor);

          MatrixCursor.RowBuilder builder1 = matrixCursor.newRow();
          builder1.add(R.drawable.ic_launcher);
          builder1.add("zhangsan");
          builder1.add(39);

          MatrixCursor.RowBuilder builder2 = matrixCursor.newRow();
          builder2.add(R.drawable.ic_launcher);
          builder2.add("lisi");
          builder2.add(40);

          MatrixCursor.RowBuilder builder3 = matrixCursor.newRow();
          builder3.add(R.drawable.ic_launcher);
          builder3.add("wangwu");
          builder3.add(41);

          setListAdapter(new SimpleCursorAdapter(this, R.layout.activity_main,
                    matrixCursor, COLUMN_NAME, new int[] { R.id.icon, R.id.name,
                              R.id.price }));
     }

     @Override
     protected void onListItemClick(ListView l, View v, int position, long id) {
          super.onListItemClick(l, v, position, id);
          matrixCursor.moveToPosition(position);
          StringBuilder builder = new StringBuilder();
          builder.append("Name:")
                    .append(matrixCursor.getString(matrixCursor
                              .getColumnIndex("name"))).append("\n");

          builder.append("Price:")
                    .append(matrixCursor.getString(matrixCursor
                              .getColumnIndex("price"))).append("\n");

          Toast.makeText(getApplicationContext(), builder.toString(), 1000)
                    .show();
     }
}

 

实现步骤仅需3步，下面通过字符数组来说明：

步骤1.首先创建一个字符数组，且字符数组的值对应着表的字段，如下：

      String[] COLUMN_NAME = { "_id", "name", "price" };

步骤2.利用MatrixCursor的构造方法，构造一个MatrixCursor，传入的参数即是步骤1中创建的字段数组，如下：

   MatrixCursormatrixCursor=newMatrixCursor(COLUMN_NAME);

也可以指定初始大小，如：

   matrixCursor=newMatrixCursor( COLUMN_NAME, 10);

步骤3. 通过matrixCursor 的addRow方法添加一行值，相当于向数据库中插入一条记录，如下：

      matrixCursor.addRow(new Object[] { R.drawable.ic_launcher, "zhangsan",39 });

注：步骤3也可以通过构造一个MatrixCursor.RowBuilder来实现，也是相当于向数据库中插入一条记录，如下：

          MatrixCursor.RowBuilder builder1 = matrixCursor.newRow();
          builder1.add(R.drawable.ic_launcher);
          builder1.add("zhangsan");
          builder1.add(39);

          //builder1.add(399999);

通过上面三步即可完成MatrixCursor 的构造。从MatrixCursor 中取出数据的过程与Cursor相同，不再赘述！

注释：如果builder1对象add的数量大于字段的个数，即打开builder1.add(399999);注释，那么将会报以下错误：

02-27 19:00:44.882: W/dalvikvm(29036): threadid=1: thread exiting with uncaught exception (group=0x41e689a8)
02-27 19:00:44.882: W/dalvikvm(29036): threadid=1: uncaught exception occurred
02-27 19:00:44.883: W/System.err(29036): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test.matrixcursor/com.test.matrixcursor.MainActivity}:android.database.CursorIndexOutOfBoundsException: No more columns left.
02-27 19:00:44.883: W/System.err(29036):      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2356)
02-27 19:00:44.883: W/System.err(29036):      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2408)
02-27 19:00:44.883: W/System.err(29036):      at android.app.ActivityThread.access$600(ActivityThread.java:167)
02-27 19:00:44.883: W/System.err(29036):      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1378)
02-27 19:00:44.883: W/System.err(29036):      at android.os.Handler.dispatchMessage(Handler.java:107)
02-27 19:00:44.883: W/System.err(29036):      at android.os.Looper.loop(Looper.java:194)
02-27 19:00:44.884: W/System.err(29036):      at android.app.ActivityThread.main(ActivityThread.java:5405)
02-27 19:00:44.884: W/System.err(29036):      at java.lang.reflect.Method.invokeNative(Native Method)
02-27 19:00:44.884: W/System.err(29036):      at java.lang.reflect.Method.invoke(Method.java:525)
02-27 19:00:44.884: W/System.err(29036):      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:838)
02-27 19:00:44.884: W/System.err(29036):      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
02-27 19:00:44.884: W/System.err(29036):      at dalvik.system.NativeStart.main(Native Method)
02-27 19:00:44.886: W/System.err(29036): Caused by: android.database.CursorIndexOutOfBoundsException: No more columns left.
02-27 19:00:44.887: W/System.err(29036):      at android.database.MatrixCursor$RowBuilder.add(MatrixCursor.java:206)
02-27 19:00:44.887: W/System.err(29036):      at com.test.matrixcursor.MainActivity.createList(MainActivity.java:46)
02-27 19:00:44.888: W/System.err(29036):      at com.test.matrixcursor.MainActivity.onCreate(MainActivity.java:20)
02-27 19:00:44.889: W/System.err(29036):      at android.app.Activity.performCreate(Activity.java:5127)
02-27 19:00:44.889: W/System.err(29036):      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1151)
02-27 19:00:44.890: W/System.err(29036):      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2320)

 

程序运行结果：