四大組件之一ContentProvider內容提供者

ContentProvider 的介紹和使用

什麼是ContentProvider？

ContentProvider內容提供者（四大組件之一）主要用於在不同的應用程序之間實現數據共享的功能，使用時需要導入註解的包並在清單文件中註冊，就是簡而言之內容提供者提供一個地址，分享內容內容解析者把uri解析一下,去指向提供者的地址

使用步驟

（1）創建數據庫，自定義類繼承SQLiteOpenHelper
（2）自定義內容提供者類，繼承ContentProvider，重寫insert/delete/update/query方法，向外界提供方法
（3）清單文件中註冊內容提供者

自定義ContentProvider

1.提供方：ContentProvider
（1）創建數據庫，自定義類繼承SQLiteOpenHelper
（2）自定義內容提供者類，繼承ContentProvider，重寫insert/delete/update/query方法，向外界提供方法
（3）清單文件中註冊內容提供者

2.索要方：ContentResolver
（1）通過Context的getContentResolver方法獲得ContentResolver對象
（2）確定uri
（3）調用insert/delete/update/query方法訪問數據庫

ContentProvider

內容解析者
（1）通過Context的getContentResolver方法獲得ContentResolver對象
（2）確定uri
（3）調用insert/delete/update/query方法訪問數據庫

自定義權限

寫在清單文件中，application外面

<permission
        android:name="com.bawei.permission.READ"
        android:protectionLevel="normal"
        >
    </permission>
    <permission
        android:name="com.bawei.permission.WRITE"
        android:protectionLevel="normal"
        >
    </permission>

內容解析方清單文件添加權限

<uses-permission android:name="com.bawei.permission.WRITE"></uses-permission>
<uses-permission android:name="com.bawei.permission.READ"></uses-permission>

基本展示案例代碼

public class MyHelper extends SQLiteOpenHelper {
    public MyHelper(Context context) {
        super(context, "user.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table user (_id integer primary key autoincrement ,name varchar(30),age integer)");
        for(int i=1;i<10;i++){
            db.execSQL("insert into user values(null,?,?)",new String[]{"非常的帥"+i+"",i+""});
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

public class MyProvider extends ContentProvider {
    private MyHelper myHelper;
    private SQLiteDatabase db;
    //獲取數據庫
    @Override
    public boolean onCreate() {
        myHelper=new MyHelper(getContext());
        db=myHelper.getWritableDatabase();
        if(db==null){
            return false;
        }else{
            return true;
        }
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        return  db.query("user",projection,selection,selectionArgs,null,null,sortOrder);
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        return null;
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        db.insert("user",null,values);
        return uri;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        return db.delete("user",selection,selectionArgs);
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        return db.update("user",values,selection,selectionArgs);
    }
}

public class Main2Activity extends AppCompatActivity {
    private ContentResolver contentResolver;
    private Uri uri;
    private Button buttonId;
    private static final String TAG = "Main2Activity";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        uri=Uri.parse("content://com.bawei");
        contentResolver=getContentResolver();


        buttonId = findViewById(R.id.button_id);
        buttonId.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
               query();
            }
        });

//
    }
    //user (_id integer primary key autoincrement ,name varchar(30),age integer)
    public void query(){
        //參數一：uri 參數二：查詢的字段 參數三：條件  參數四：爲?賦值 參數五：排序
        Toast.makeText(this, "cha", Toast.LENGTH_SHORT).show();
        Cursor cursor=contentResolver.query(uri,new String[]{"_id","name"},null,null,null);
        while (cursor.moveToNext()){
            String name = cursor.getString(cursor.getColumnIndex("name"));
            Log.i(TAG, "query: "+name);
            Toast.makeText(this, name, Toast.LENGTH_SHORT).show();
        }
        //遍歷
    }
    public  void delete(){
        //參數一：uri  參數二：條件 參數三：爲?賦值
        int raw=contentResolver.delete(uri,"name=?",new String[]{"非常的帥1"});
    }
    public void insert(){
        //添加數據
        ContentValues contentValues=new ContentValues();
        contentValues.put("name","要甜雪");
        contentValues.put("age",18);
        contentResolver.insert(uri,contentValues);
        //遍歷
    }
}

通訊錄案例代碼

創建外部類儲存聯繫人信息

public class Phone {
    private String name;
    private String number;

    public Phone() {
    }

    public Phone(String name, String number) {
        this.name = name;
        this.number = number;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    @Override
    public String toString() {
        return "Phone{" +
                "name='" + name + '\'' +
                ", number='" + number + '\'' +
                '}';
    }
}

主函數獲取通訊錄

public class MainActivity extends AppCompatActivity {
    private Button buttonId;

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

        buttonId = findViewById(R.id.button_id);

        buttonId.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            //根據版本動態獲取授權(6.0以上)
                if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.M){
                   requestPermissions(new String[]{Manifest.permission.WRITE_CONTACTS,Manifest.permission.READ_CONTACTS},100);
                }else{
                    resolverMethod();
                }
            }
        });
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if(requestCode == 100 & grantResults[0] == PackageManager.PERMISSION_GRANTED){
            resolverMethod();
        }
    }

    //因爲重複使用,所有封裝
    private void resolverMethod() {
        ContentResolver contentResolver = getContentResolver();
        Uri uri = ContactsContract.CommonDataKinds.Phone.CONTENT_URI;
        String[] strings = {ContactsContract.CommonDataKinds.Phone.NUMBER, ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME};
        Cursor cursor = contentResolver.query(uri, strings, null, null, null);
        while (cursor.moveToNext()){
            String name = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
            String number = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
            Toast.makeText(MainActivity.this, name, Toast.LENGTH_SHORT).show();
            //有了對象,其他都好說了.
            Phone phone = new Phone(name, number);
        }
    }
}