Android(安卓)浅谈MatrixCursor
16lz
2021-12-04
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
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:
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:
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:
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