Android ListActivity没有'；t在数据到达时更新

我正在构建一个小应用程序，我希望在新数据到达时自动更新它

从我读到的android文档来看，我认为因为我使用了更新的技术，ContentObserver将在后台为我创建，我只会自动调用加载程序

如果有更多有用的信息，我很乐意添加，或者将整个项目上传到某个地方

此外，我的目标是KitKat（sdk版本19）

应用程序概述

我们有一个使用内置ListView的ListActivity

ListActivity通过使用加载器和SimpleCursorAdapter获取数据

加载程序通过查询ContentProvider来检索其数据

ContentProvider由SQLite数据库支持

此外，在操作栏中，我添加了两个操作，一个用于添加项目，另一个用于清除所有项目

当我添加项目时，ListView不会用新条目更新，我还可以看到ContentProvider上没有运行新的查询。如果关闭并重新启动应用程序，这些条目现在在ListView中可见

源代码如下 Activity.java

package us.lynch.listdemo;

import java.text.DateFormat;
import java.util.Date;

import us.lynch.listdemo.R;
import android.app.ListActivity;
import android.app.LoaderManager.LoaderCallbacks;
import android.content.ContentValues;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.CursorAdapter;
import android.widget.SimpleCursorAdapter;

public class Activity extends ListActivity implements LoaderCallbacks<Cursor> {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setListAdapter(new SimpleCursorAdapter(this, R.layout.listitem, null, new String[] { "string" }, new int[] { R.id.text }, 0));
        getLoaderManager().initLoader(0, null, this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        ContentValues values = new ContentValues();

        switch (item.getItemId()) {
            case R.id.action_add:
                values.put("string", DateFormat.getDateTimeInstance().format(new Date()));
                getContentResolver().insert(Uri.parse("content://us.lynch.listdemo/data"), values);
                return true;

            case R.id.action_clear:
                getContentResolver().delete(Uri.parse("content://us.lynch.listdemo/data"), null, null);
                return true;

            default:
                return super.onOptionsItemSelected(item);
        }
    }

    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        Uri uri = Uri.parse("content://us.lynch.listdemo/data");
        String[] projection = { "_id", "string" };
        return new CursorLoader(this, uri, projection, null, null, "_id");
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
        ((CursorAdapter) getListAdapter()).swapCursor(cursor);
    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        ((CursorAdapter) getListAdapter()).swapCursor(null);
    }
}

package us.lynch.listdemo;

import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.DatabaseUtils;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;
import android.text.TextUtils;

public class ContentProvider extends android.content.ContentProvider {
    private static final UriMatcher sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    private Database mDatabase;

    private static final int MATCH = 1;
    private static final int MATCH_ID = 2;

    static {
        sUriMatcher.addURI("us.lynch.listdemo", "data", MATCH);
        sUriMatcher.addURI("us.lynch.listdemo", "data/#", MATCH_ID);
    }

    @Override
    public boolean onCreate() {
        mDatabase = new Database(getContext());
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        switch (sUriMatcher.match(uri)) {
            case MATCH:
                return database().query("data", projection, selection, selectionArgs, null, null, sortOrder);
            case MATCH_ID:
                selection = addIdToSelection(uri, selection);
                return database().query("data", projection, selection, selectionArgs, null, null, sortOrder);
            default:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        switch (sUriMatcher.match(uri)) {
            case MATCH: {
                return ContentUris.withAppendedId(uri, database().insertOrThrow("data", null, values));
            }
            default:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        switch (sUriMatcher.match(uri)) {
            case MATCH:
                return database().delete("data", selection, selectionArgs);
            case MATCH_ID:
                selection = addIdToSelection(uri, selection);
                return database().delete("data", selection, selectionArgs);
            default:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        switch (sUriMatcher.match(uri)) {
            case MATCH:
                return database().update("data", values, selection, selectionArgs);
            case MATCH_ID:
                selection = addIdToSelection(uri, selection);
                return database().update("data", values, selection, selectionArgs);
            default:
                throw new IllegalArgumentException("Unknown URI " + uri);
        }
    }

    @Override
    public String getType(Uri uri) {
        throw new IllegalArgumentException("Unknown URI " + uri);
    }

    private SQLiteDatabase database() {
        return mDatabase.getWritableDatabase();
    }

    private static String addIdToSelection(Uri uri, String selection) {
        return DatabaseUtils.concatenateWhere(selection, "_id = " + Long.toString(ContentUris.parseId(uri)));
    }
}

class Database extends SQLiteOpenHelper {
    Database(Context context) {
        super(context, "database", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase database) {
        final String[] columns = new String[] {
                "_id integer primary key autoincrement",
                "string text not null",
        };

        database.execSQL("create table data (" + TextUtils.join(",", columns) + ");");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        assert (false);
    }
}

res/layout/listitem.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:text="Large Text"
        android:textAppearance="?android:attr/textAppearanceLarge" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <item
        android:id="@+id/action_clear"
        android:title="Clear Items"
        android:visible="true">
    </item>
    <item
        android:id="@+id/action_add"
        android:title="Add Item"
        android:visible="true">
    </item>

</menu>

res/menu/main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:text="Large Text"
        android:textAppearance="?android:attr/textAppearanceLarge" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <item
        android:id="@+id/action_clear"
        android:title="Clear Items"
        android:visible="true">
    </item>
    <item
        android:id="@+id/action_add"
        android:title="Add Item"
        android:visible="true">
    </item>

</menu>

---

您不使用

Uri

通知机制

在query（）方法中写入：

Cursor cursor = database().query("data", projection, selection, selectionArgs, null, null, sortOrder);
cursor.setNotificationUri(getContext().getContentResolver(), uri);
return cursor;

在修改内容的方法（插入、更新、删除）中，通知相同的Uri：

ContentResolver cr = getContext().getContentResolver();
cr.notifyChange(uri, null);

---

这很有趣。我以前尝试过

notifyChange（）

部分，但没有看到

setNotificationUri（）

。测试这个。你确实也需要那个。加载程序将在后台重新加载查询（Uri必须相同）