Android应用程序组件Content Provider应用实例（3）-白红宇

下面是ArticlesAdapter类的实现，它实现在src/shy/luo/ArticlesAdapter.java文件中：

package shy.luo.article;

import java.util.LinkedList;

import shy.luo.providers.articles.Articles;

import android.content.ContentResolver;

import android.content.ContentUris;

import android.content.ContentValues;

import android.content.Context;

import android.content.IContentProvider;

import android.database.Cursor;

import android.net.Uri;

import android.os.Bundle;

import android.os.RemoteException;

import android.util.Log;

public class ArticlesAdapter {

private static final String LOG_TAG = "shy.luo.article.ArticlesAdapter";

private ContentResolver resolver = null;

public ArticlesAdapter(Context context) {

resolver = context.getContentResolver();

}

public long insertArticle(Article article) {

ContentValues values = new ContentValues();

values.put(Articles.TITLE, article.getTitle());

values.put(Articles.ABSTRACT, article.getAbstract());

values.put(Articles.URL, article.getUrl());

Uri uri = resolver.insert(Articles.CONTENT_URI, values);

String itemId = uri.getPathSegments().get(1);

return Integer.valueOf(itemId).longValue();

}

public boolean updateArticle(Article article) {

Uri uri = ContentUris.withAppendedId(Articles.CONTENT_URI, article.getId());

ContentValues values = new ContentValues();

values.put(Articles.TITLE, article.getTitle());

values.put(Articles.ABSTRACT, article.getAbstract());

values.put(Articles.URL, article.getUrl());

int count = resolver.update(uri, values, null, null);

return count > 0;

}

public boolean removeArticle(int id) {

Uri uri = ContentUris.withAppendedId(Articles.CONTENT_URI, id);

int count = resolver.delete(uri, null, null);

return count > 0;

}

public LinkedList<Article> getAllArticles() {

LinkedList<Article> articles = new LinkedList<Article>();

String[] projection = new String[] {

Articles.ID,

Articles.TITLE,

Articles.ABSTRACT,

Articles.URL

};

Cursor cursor = resolver.query(Articles.CONTENT_URI, projection, null, null, Articles.DEFAULT_SORT_ORDER);

if (cursor.moveToFirst()) {

do {

int id = cursor.getInt(0);

String title = cursor.getString(1);

String abs = cursor.getString(2);

String url = cursor.getString(3);

Article article = new Article(id, title, abs, url);

articles.add(article);

} while(cursor.moveToNext());

}

return articles;

}

public int getArticleCount() {

int count = 0;

try {

IContentProvider provider = resolver.acquireProvider(Articles.CONTENT_URI);

Bundle bundle = provider.call(Articles.METHOD_GET_ITEM_COUNT, null, null);

count = bundle.getInt(Articles.KEY_ITEM_COUNT, 0);

} catch(RemoteException e) {

e.printStackTrace();

}

return count;

}

public Article getArticleById(int id) {

Uri uri = ContentUris.withAppendedId(Articles.CONTENT_URI, id);

String[] projection = new String[] {

Articles.ID,

Articles.TITLE,

Articles.ABSTRACT,

Articles.URL

};

Cursor cursor = resolver.query(uri, projection, null, null, Articles.DEFAULT_SORT_ORDER);

Log.i(LOG_TAG, "cursor.moveToFirst");

if (!cursor.moveToFirst()) {

return null;

}

String title = cursor.getString(1);

String abs = cursor.getString(2);

String url = cursor.getString(3);

return new Article(id, title, abs, url);

}

public Article getArticleByPos(int pos) {

Uri uri = ContentUris.withAppendedId(Articles.CONTENT_POS_URI, pos);

String[] projection = new String[] {

Articles.ID,

Articles.TITLE,

Articles.ABSTRACT,

Articles.URL

};

Cursor cursor = resolver.query(uri, projection, null, null, Articles.DEFAULT_SORT_ORDER);

if (!cursor.moveToFirst()) {

return null;

}

int id = cursor.getInt(0);

String title = cursor.getString(1);

String abs = cursor.getString(2);

String url = cursor.getString(3);

return new Article(id, title, abs, url);

}

}

这个类首先在构造函数里面获得应用程序上下文的ContentResolver接口，然后通过就可以通过这个接口来访问ArticlesProvider中的文章信息了。成员函数insertArticle、updateArticle和removeArticle分别用来新增、更新和删除一个文章信息条目；成员函数getAllArticlese用来获取所有的文章信息；成员函数getArticleById和getArticleByPos分别根据文章的ID和位置来获得具体文章信息条目；成员函数getArticleCount直接使用ContentProvider的未公开接口call来获得文章信息条目的数量，注意，这个函数要源代码环境下编译才能通过。

下面是程序主界面MainActivity类的实现，它实现在src/shy/luo/article/MainActivity.java文件中：

package shy.luo.article;

import shy.luo.providers.articles.Articles;

import android.app.Activity;

import android.content.Context;

import android.content.Intent;

import android.database.ContentObserver;

import android.os.Bundle;

import android.os.Handler;

import android.util.Log;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.AdapterView;

import android.widget.BaseAdapter;

import android.widget.Button;

import android.widget.ListView;

import android.widget.TextView;

public class MainActivity extends Activity implements View.OnClickListener, AdapterView.OnItemClickListener {

private final static String LOG_TAG = "shy.luo.article.MainActivity";

private final static int ADD_ARTICAL_ACTIVITY = 1;

private final static int EDIT_ARTICAL_ACTIVITY = 2;

private ArticlesAdapter aa = null;

private ArticleAdapter adapter = null;

private ArticleObserver observer = null;

private ListView articleList = null;

private Button addButton = null;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

aa = new ArticlesAdapter(this);

articleList = (ListView)findViewById(R.id.listview_article);

adapter = new ArticleAdapter(this);

articleList.setAdapter(adapter);

articleList.setOnItemClickListener(this);

observer = new ArticleObserver(new Handler());

getContentResolver().registerContentObserver(Articles.CONTENT_URI, true, observer);

addButton = (Button)findViewById(R.id.button_add);

addButton.setOnClickListener(this);

Log.i(LOG_TAG, "MainActivity Created");

}

@Override

public void onDestroy() {

super.onDestroy();

getContentResolver().unregisterContentObserver(observer);

}

@Override

public void onClick(View v) {

if(v.equals(addButton)) {

Intent intent = new Intent(this, ArticleActivity.class);

startActivityForResult(intent, ADD_ARTICAL_ACTIVITY);

}

}

@Override

public void onItemClick(AdapterView<?> parent, View view, int pos, long id) {

Intent intent = new Intent(this, ArticleActivity.class);

Article article = aa.getArticleByPos(pos);

intent.putExtra(Articles.ID, article.getId());

intent.putExtra(Articles.TITLE, article.getTitle());

intent.putExtra(Articles.ABSTRACT, article.getAbstract());

intent.putExtra(Articles.URL, article.getUrl());

startActivityForResult(intent, EDIT_ARTICAL_ACTIVITY);

}

@Override

public void onActivityResult(int requestCode,int resultCode, Intent data) {

super.onActivityResult(requestCode, resultCode, data);

switch(requestCode) {

case ADD_ARTICAL_ACTIVITY: {

if(resultCode == Activity.RESULT_OK) {

String title = data.getStringExtra(Articles.TITLE);

String abs = data.getStringExtra(Articles.ABSTRACT);

String url = data.getStringExtra(Articles.URL);

Article article = new Article(-1, title, abs, url);

aa.insertArticle(article);

}

break;

}

case EDIT_ARTICAL_ACTIVITY: {

if(resultCode == Activity.RESULT_OK) {

int action = data.getIntExtra(ArticleActivity.EDIT_ARTICLE_ACTION, -1);

if(action == ArticleActivity.MODIFY_ARTICLE) {

int id = data.getIntExtra(Articles.ID, -1);

String title = data.getStringExtra(Articles.TITLE);

String abs = data.getStringExtra(Articles.ABSTRACT);

String url = data.getStringExtra(Articles.URL);

Article article = new Article(id, title, abs, url);

aa.updateArticle(article);

} else if(action == ArticleActivity.DELETE_ARTICLE) {

int id = data.getIntExtra(Articles.ID, -1);

aa.removeArticle(id);

}

}

break;

}

}

}

private class ArticleObserver extends ContentObserver {

public ArticleObserver(Handler handler) {

super(handler);

}

@Override

public void onChange (boolean selfChange) {

adapter.notifyDataSetChanged();

}

}

private class ArticleAdapter extends BaseAdapter {

private LayoutInflater inflater;

public ArticleAdapter(Context context){

inflater = LayoutInflater.from(context);

}

@Override

public int getCount() {

return aa.getArticleCount();

}

@Override

public Object getItem(int pos) {

return aa.getArticleByPos(pos);

}

@Override

public long getItemId(int pos) {

return aa.getArticleByPos(pos).getId();

}

@Override

public View getView(int position, View convertView, ViewGroup parent) {

Article article = (Article)getItem(position);

if (convertView == null) {

convertView = inflater.inflate(R.layout.item, null);

}

TextView titleView = (TextView)convertView.findViewById(R.id.textview_article_title);

titleView.setText("Title: " + article.getTitle());

TextView abstractView = (TextView)convertView.findViewById(R.id.textview_article_abstract);

abstractView.setText("Abstract: " + article.getAbstract());

TextView urlView = (TextView)convertView.findViewById(R.id.textview_article_url);

urlView.setText("URL: " + article.getUrl());

return convertView;

}

}

}

在应用程序的主界面中，我们使用一个ListView来显示文章信息条目，这个ListView的数据源由ArticleAdapter类来提供，而ArticleAdapter类又是通过ArticlesAdapter类来获得ArticlesProvider中的文章信息的。在MainActivity的onCreate函数，我们还通过应用程序上下文的ContentResolver接口来注册了一个ArticleObserver对象来监控ArticlesProvider中的文章信息。一旦ArticlesProvider中的文章信息发生变化，就会通过ArticleAdapter类来实时更新ListView中的文章信息。

下面是ArticleActivity类的实现，它实现在src/shy/luo/article/ArticleActivity.java文件中：

package shy.luo.article;

import shy.luo.providers.articles.Articles;

import android.app.Activity;

import android.content.Intent;

import android.os.Bundle;

import android.util.Log;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

public class ArticleActivity extends Activity implements View.OnClickListener {

private final static String LOG_TAG = "shy.luo.article.ArticleActivity";

public final static String EDIT_ARTICLE_ACTION = "EDIT_ARTICLE_ACTION";

public final static int MODIFY_ARTICLE = 1;

public final static int DELETE_ARTICLE = 2;

private int articleId = -1;

private EditText titleEdit = null;

private EditText abstractEdit = null;

private EditText urlEdit = null;

private Button addButton = null;

private Button modifyButton = null;

private Button deleteButton = null;

private Button cancelButton = null;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.article);

titleEdit = (EditText)findViewById(R.id.edit_article_title);

abstractEdit = (EditText)findViewById(R.id.edit_article_abstract);

urlEdit = (EditText)findViewById(R.id.edit_article_url);

addButton = (Button)findViewById(R.id.button_add_article);

addButton.setOnClickListener(this);

modifyButton = (Button)findViewById(R.id.button_modify);

modifyButton.setOnClickListener(this);

deleteButton = (Button)findViewById(R.id.button_delete);

deleteButton.setOnClickListener(this);

cancelButton = (Button)findViewById(R.id.button_cancel);

cancelButton.setOnClickListener(this);

Intent intent = getIntent();

articleId = intent.getIntExtra(Articles.ID, -1);

if(articleId != -1) {

String title = intent.getStringExtra(Articles.TITLE);

titleEdit.setText(title);

String abs = intent.getStringExtra(Articles.ABSTRACT);

abstractEdit.setText(abs);

String url = intent.getStringExtra(Articles.URL);

urlEdit.setText(url);

addButton.setVisibility(View.GONE);

} else {

modifyButton.setVisibility(View.GONE);

deleteButton.setVisibility(View.GONE);

}

Log.i(LOG_TAG, "ArticleActivity Created");

}

@Override

public void onClick(View v) {

if(v.equals(addButton)) {

String title = titleEdit.getText().toString();

String abs = abstractEdit.getText().toString();

String url = urlEdit.getText().toString();

Intent result = new Intent();

result.putExtra(Articles.TITLE, title);

result.putExtra(Articles.ABSTRACT, abs);

result.putExtra(Articles.URL, url);

setResult(Activity.RESULT_OK, result);

finish();

} else if(v.equals(modifyButton)){

String title = titleEdit.getText().toString();

String abs = abstractEdit.getText().toString();

String url = urlEdit.getText().toString();

Intent result = new Intent();

result.putExtra(Articles.ID, articleId);

result.putExtra(Articles.TITLE, title);

result.putExtra(Articles.ABSTRACT, abs);

result.putExtra(Articles.URL, url);

result.putExtra(EDIT_ARTICLE_ACTION, MODIFY_ARTICLE);

setResult(Activity.RESULT_OK, result);

finish();

} else if(v.equals(deleteButton)) {

Intent result = new Intent();

result.putExtra(Articles.ID, articleId);

result.putExtra(EDIT_ARTICLE_ACTION, DELETE_ARTICLE);

setResult(Activity.RESULT_OK, result);

finish();

} else if(v.equals(cancelButton)) {

setResult(Activity.RESULT_CANCELED, null);

finish();

}

}

}

在ArticleActivity窗口中，我们可以执行新增、更新和删除文章信息的操作。如果启动ArticleActivity时，没有把文章ID传进来，就说明要执行操作是新增文章信息；如果启动ArticleActivity时，把文章ID和其它信自都传进来了，就说明要执行的操作是更新或者删除文章，根据用户在界面点击的是更新按钮还是删除按钮来确定。

本文转自 Luoshengyang 51CTO博客，原文链接：http://blog.51cto.com/shyluo/966942，如需转载请自行联系原作者