1.权限种类

1.1权限种类区分-普通权限、危险权限、特殊权限

首先 Android 的权限大致分为三种：
普通权限：只需要在清单文件中注册即可
危险权限：需要在代码中动态申请，以弹系统 Dialog 的形式进行请求
特殊权限：需要在代码中动态申请，以跳系统 Activity 的形式进行请求

1.2存储权限-变化

存储权限：
在 Android 6.0 之后就变成了危险权限；
在 Android 11 上面变成了特殊权限；
申请方式的发生了不同

2.外部存储和内部存储对比

2.1外部存储在手机哪个位置？

Android4.4之前：
内部存储在手机ROM上的一块存储区域；
外部存储在SD卡上；

Android4.4之后：
内部存储在手机ROM上的一块存储区域；
外部存储也在手机ROM上的一块存储区域；

2.2外部存储和内部存储的访问权限区别

3.外部存储适配方案

3.1 Android 10.0 以下外部存储权限适配

• 升级 targetSdkVersion

android 
    defaultConfig {
        targetSdkVersion 23
    }
}

• 添加清单权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

• 如果 targetSdkVersion >= 29 上，还需要在清单文件中加上

<application
    android:requestLegacyExternalStorage="true">

• 代码动态申请

public final class PermissionActivity extends AppCompatActivity {

    private static final int REQUEST_CODE = 1024;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestPermission();
    }

    private void requestPermission() {
    	//判断版本大于等于android 6.0
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            // 先判断有没有权限
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED &&
                    ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
                writeFile();
            } else {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CODE);
            }
        } else {
            writeFile();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == REQUEST_CODE) {
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED &&
                    ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
                writeFile();
            } else {
                ToastUtils.show("存储权限获取失败");
            }
        }
    }

    /**
     * 模拟文件写入
     */
    private void writeFile() {
        ToastUtils.show("写入文件成功");
    }
}

3.2 Android 11 及以上申请外部存储权限

• 升级 targetSdkVersion

android 
    defaultConfig {
        targetSdkVersion 30
    }
}

• 添加清单权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />

• 代码动态申请

public final class PermissionActivity extends AppCompatActivity {

    private static final int REQUEST_CODE = 1024;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestPermission();
    }

    private void requestPermission() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
            // 先判断有没有权限
            if (Environment.isExternalStorageManager()) {
                writeFile();
            } else {
                Intent intent = new Intent(Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION);
                intent.setData(Uri.parse("package:" + context.getPackageName()));
                startActivityForResult(intent, REQUEST_CODE);
            }
        } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            // 先判断有没有权限
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED &&
                    ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
                writeFile();
            } else {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CODE);
            }
        } else {
            writeFile();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == REQUEST_CODE) {
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED &&
                    ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
                writeFile();
            } else {
                ToastUtils.show("存储权限获取失败");
            }
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == REQUEST_CODE && Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
            if (Environment.isExternalStorageManager()) {
                writeFile();
            } else {
                ToastUtils.show("存储权限获取失败");
            }
        }
    }

    /**
     * 模拟文件写入
     */
    private void writeFile() {
        ToastUtils.show("写入文件成功");
    }
}

4.权限申请框架推荐

4.1 XXPermissions

4.1 AndPermission