Android 11访问外部文件，又增加额外权限，需要另外申请A

Android 陈芝麻烂谷子，屁事儿真多，提高版本，就会增加额外的权限；原有的项目，莫名其妙的就运行时发生崩溃；

从发展的角度，Android的确越来越完善，但是这期间，新老版本的升级和过渡，对开发者确实不是很好友的，尤其是对于新手，需要考虑的事情太多，对老版本项目的理解，更是困难；

Android 11
如果需要支持Android 11（targetSDKVersion 30），那么就需要在AndroidManifest.xml中下列权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"
    android:maxSdkVersion="28" />
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />

对于Android 10，还有设置

android:requestLegacyExternalStorage="true"

下面的方法是检查权限是否已授权或拒绝

private boolean checkPermission() {
    if (SDK_INT >= Build.VERSION_CODES.R) {
        return Environment.isExternalStorageManager();
    } else {
        int result = ContextCompat.checkSelfPermission(PermissionActivity.this, READ_EXTERNAL_STORAGE);
        int result1 = ContextCompat.checkSelfPermission(PermissionActivity.this, WRITE_EXTERNAL_STORAGE);
        return result == PackageManager.PERMISSION_GRANTED && result1 == PackageManager.PERMISSION_GRANTED;
    }
}

下面的方法可以用于在Android 11及较低版本申请权限：

private void requestPermission() {
    if (SDK_INT >= Build.VERSION_CODES.R) {
        try {
            Intent intent = new Intent(Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION);
            intent.addCategory("android.intent.category.DEFAULT");
            intent.setData(Uri.parse(String.format("package:%s",getApplicationContext().getPackageName())));
            startActivityForResult(intent, 2296);
        } catch (Exception e) {
            Intent intent = new Intent();
            intent.setAction(Settings.ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION);
            startActivityForResult(intent, 2296);
        }
    } else {
        //below android 11
        ActivityCompat.requestPermissions(PermissionActivity.this, new String[]{WRITE_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
    }
}

Android 11及更高版本，处理权限回调

@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == 2296) {
        if (SDK_INT >= Build.VERSION_CODES.R) {
            if (Environment.isExternalStorageManager()) {
                // perform action when allow permission success
            } else {
                Toast.makeText(this, "Allow permission for storage access!", Toast.LENGTH_SHORT).show();
            }
        }
    }
}

Android 11以下版本，处理权限回调

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
    switch (requestCode) {
        case PERMISSION_REQUEST_CODE:
            if (grantResults.length > 0) {
                boolean READ_EXTERNAL_STORAGE = grantResults[0] == PackageManager.PERMISSION_GRANTED;
                boolean WRITE_EXTERNAL_STORAGE = grantResults[1] == PackageManager.PERMISSION_GRANTED;

                if (READ_EXTERNAL_STORAGE && WRITE_EXTERNAL_STORAGE) {
                    // perform action when allow permission success
                } else {
                    Toast.makeText(this, "Allow permission for storage access!", Toast.LENGTH_SHORT).show();
                }
            }
            break;
    }
}

注意：MANAGE_EXTERNAL_STORAGE是特殊权限，只有少数应用才被允许，比如反病毒、文件管理等。在上架应用市场时，可能需要说明原因。