内容提供器

1.权限机制

添加权限后

• 用户在安装时知道程序需要哪些权限。
• 用户在程序管理界面查看程序申请了哪些权限。

  2.运行时权限

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button makeCall = findViewById(R.id.make_call);
        makeCall.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CALL_PHONE) != PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(MainActivity.this, new String[]{
                        Manifest.permission.CALL_PHONE
                        }, 1);
                } else {
                    call();
                }
            }
        });
    }
    private void call() {
        try {
            Intent intent = new Intent(Intent.ACTION_CALL);
            intent.setData(Uri.parse("tel:10086"));
            startActivity(intent);
        } catch (SecurityException e) {
            e.printStackTrace();
        }
    }
    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case 1:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    call();
                } else {
                    Toast.makeText(MainActivity.this, "You denied the permission", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }
}

3. 访问其他程序中的数据

内容提供器分为系统内置和 自定义实现的内容提供器。应用程序通过内容提供器对其数据提供了外部访问接口。Android系统中自带的电话簿，短信，媒体库等程序都提供了类似的访问接口。

ContentResolver**

应用程序通过ContentResolver类来访问其他应用程序共享的数据，可以通过Context中的getContentResolver()方法获取到该类的实例。

package com.example.contactstest;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import android.Manifest;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.Currency;
import java.util.List;
public class MainActivity extends AppCompatActivity {
    ArrayAdapter<String> adapter;
    List<String> contactList = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView contactView = (ListView) findViewById(R.id.contacts_view);
        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, contactList);
        contactView.setAdapter(adapter);
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_CONTACTS) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{
                Manifest.permission.READ_CONTACTS
                }, 1);
        } else {
            readContacts();
        }
    }
    private void readContacts() {
        Cursor cursor = null;
        try {
            cursor = getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI, null, null, null, null);
            if (cursor != null) {
                while (cursor.moveToNext()) {
                    String displayName = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
                    String number = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
                    contactList.add(displayName + "\n" + number);
                }
                adapter.notifyDataSetChanged();
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }
    }
    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int [] grantResults) {
        switch (requestCode) {
            case 1:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    readContacts();
                } else {
                    Toast.makeText(this, "You denied the permission", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }
}

4.创建自己的内容提供器

TODO