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WeiCzai authored Jan 8, 2021
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# 实验五：Android存储编程

## 一、实验目标

1. 了解Andoid的存储手段
2. 掌握Android的文件存储
3. 掌握Android的数据库存储

## 二、实验内容

1. 将应用产生的数据保存到文件存储中；
2. 使用文件外部存储方式
3. 运行结果截图。

## 三、实验步骤

1. 建立自己用于保存图片相关信息的Activity
```java
public class ContentProviderActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_content_provider);

final ContentProviderActivity thisActivity = this;

// 保存图片信息
findViewById(R.id.button_save).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
thisActivity.savePicture();
}
});

// 加载下一张图片信息
findViewById(R.id.button_next).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
thisActivity.showNextPicture();
}
});

}

// 保存图片信息
private void savePicture() {
String name = ((EditText) findViewById(R.id.picture_name)).getText().toString();
String tags = ((EditText) findViewById(R.id.picture_tags)).getText().toString();

// 插入新记录
ContentValues picture = new ContentValues();
picture.put(ContentProviderOfPicture.NAME, name);
picture.put(ContentProviderOfPicture.TAGS, tags);
Uri uri = getContentResolver() // 执行插入操作
.insert(ContentProviderOfPicture.CONTENT_URI, picture);

Toast.makeText(getBaseContext(), //
"保存成功! \n" + uri.toString(), Toast.LENGTH_LONG).show();

this.showPictureInfo("", ""); // 清除内容
}

private void showPictureInfo(String name, String tags) {
((EditText) findViewById(R.id.Picture_name)).setText(name);
((EditText) findViewById(R.id.Picture_tags)).setText(tags);
}

// 显示下一张图片
private void showNextPicture() {
Cursor c = getContentResolver() // 执行查询
.query(ContentProviderOfPicture.CONTENT_URI, null, null, null, null);

// 随机取1条记录
int random = (new Random()).nextInt(10);

if (c.moveToFirst()) {
String name = "";
String tags = "";
int count = 1;
do {
name = c.getString(c.getColumnIndex(ContentProviderOfPicture.NAME));
tags = c.getString(c.getColumnIndex(ContentProviderOfPicture.TAGS));
if (count++ == random) {
break;
}
} while (c.moveToNext());
// 显示在界面上
this.showPictureInfo(name, tags);
} else {
Toast.makeText(getBaseContext(), //
"没有可显示的图片!", Toast.LENGTH_LONG).show();
}
}
}
```
2. 创建java类ContentProviderOfPicture实现用于操作数据库
```java
public class ContentProviderOfPicture extends ContentProvider {




static final String PROVIDER_NAME = "edu.hzuapps.androidlabs.tuku";
static final String URL = "content://" + PROVIDER_NAME + "/picture";
static final Uri CONTENT_URI = Uri.parse(URL);

static final String _ID = "_id";
static final String NAME = "name";
static final String TAGS = "tags";

static final int Picture = 1;
static final int Picture_ID = 2;

static final UriMatcher uriMatcher;

static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(PROVIDER_NAME, "Picture", Picture);
uriMatcher.addURI(PROVIDER_NAME, "Picture/#", Picture_ID);
}

// 数据库相关操作
private SQLiteDatabase db;
static final String DATABASE_NAME = "tuku";
static final String TABLE_Picture = "Picture";
static final int DATABASE_VERSION = 1;
static final String CREATE_DB_TABLE =
" CREATE TABLE " + TABLE_Picture +
" (_id INTEGER PRIMARY KEY AUTOINCREMENT, " +
" name TEXT NOT NULL, " +
" tags TEXT NOT NULL);";

/**
* 用于创建数据库的帮助类
*/
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_DB_TABLE);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_Picture);
// backup data, recover data
onCreate(db);
}
}

private static HashMap<String, String> DRESS_PROJECTION_MAP;

public ContentProviderOfPicture() {
}

@Override
public String getType(Uri uri) {switch (uriMatcher.match(uri)){
case Picture:
return "vnd.android.cursor.dir/vnd.example.students";
case Picture_ID:
return "vnd.android.cursor.item/vnd.example.students";

default:
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
}

// 初始化内容提供器
@Override
public boolean onCreate() {
Context context = getContext(); // Activity
DatabaseHelper dbHelper = new DatabaseHelper(context);
// 创建可写的数据库（如果没有则新建）
this.db = dbHelper.getWritableDatabase(); // insert, update, delete
//db = dbHelper.getReadableDatabase() // query (select)
return (db == null) ? false : true;
}

// 插入|保存一条记录
@Override
public Uri insert(Uri uri, ContentValues values) {
long rowID = db.insert(TABLE_Picture, "", values);
if (rowID > 0) {
Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
getContext().getContentResolver().notifyChange(_uri, null);
return _uri;
}
throw new SQLException("无法插入数据 " + uri);
}

// 查询记录
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
qb.setTables(TABLE_Picture);

switch (uriMatcher.match(uri)) {
case Picture:
qb.setProjectionMap(DRESS_PROJECTION_MAP);
break;

case Picture_ID:
qb.appendWhere(_ID + "=" + uri.getPathSegments().get(1));
break;

default:
throw new IllegalArgumentException("Unknown URI " + uri);
}

if (sortOrder == null || sortOrder == "") {
sortOrder = NAME;
}
Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, sortOrder);
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}

@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
int count = 0;
switch (uriMatcher.match(uri)) {
case Picture:
count = db.update(TABLE_Picture, values, selection, selectionArgs);
break;

case Picture_ID:
count = db.update(TABLE_Picture, values, _ID + " = " + uri.getPathSegments().get(1) +
(!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : ""), selectionArgs);
break;

default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}

@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
int count = 0;
switch (uriMatcher.match(uri)) {
case Picture:
count = db.delete(TABLE_Picture, selection, selectionArgs);
break;

case Picture_ID:
String id = uri.getPathSegments().get(1);
count = db.delete(TABLE_Picture, _ID + " = " + id +
(!TextUtils.isEmpty(selection) ? " AND (" + selection + ')' : ""), selectionArgs);
break;

default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
}
```

3.对activity_content_provider.xml进行一些页面的设计
```xml
<RelativeLayout


android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="edu.hzuapps.net1814080903301.ContentProviderActivity">

<TextView
android:id="@+id/Picture_title"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="30dp"
android:text="图片信息"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"/>

<ImageView
android:id="@+id/picture_cover"
android:layout_width="256px"
android:layout_height="256px"
android:src="@drawable/tuku"
android:layout_below="@+id/Picture_title"
android:layout_centerHorizontal="true"/>

<EditText
android:id="@+id/picture_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="图片名"
android:layout_below="@+id/picture_cover"
android:layout_centerHorizontal="true"/>

<EditText
android:id="@+id/picture_tags"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="图片备注信息"
android:layout_below="@+id/picture_name"
android:layout_centerHorizontal="true"/>

<Button
android:id="@+id/button_save"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="保存"
android:layout_below="@+id/picture_tags"
android:layout_alignParentLeft="true"/>

<Button
android:id="@+id/button_next"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="下一张图片"
android:layout_below="@+id/picture_tags"
android:layout_alignParentRight="true"/>

</RelativeLayout>
```
## 四、运行结果及截图

![avatar](https://raw.githubusercontent.com/WeiCzai/android-labs-2020/master/students/net1814080903315/labs5.png)

## 五、实验心得

这次实验内容主要是了解安卓的储存机制，学习了老师给的例子，了解了相关知识，进行修改添加，从未想过可以给每张图片加上描述，就是可以给每个图片都可以做上备注。运行时候也有有很多问题，百度查找资料
解决了。

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