当应用程序启动时，我们会显示启动屏幕，并且还会请求读取/写入 SD 卡的权限。从开始的活动开始，2 秒后，有一个过渡到另一个活动。用户没有时间阅读权限请求，对话框仍然挂在应用程序“后面”。告诉我在处理权限请求对话框后如何转换到另一个活动？或者如何将请求对话框带到前台。这是活动代码：
public class WelcomeActivity extends AppCompatActivity {
private ArrayList<String> urlsFromServer = new ArrayList<>();
private ArrayList<Uri> filesPath = new ArrayList<>();
private boolean CheckFileStorage = false;
private final int MY_PERMISSIONS_REQUEST_CODE = 1;
private String fileNamePath = "filesPath.json";
private String urlServerJson = "http://*****.ru/todbook/booklist.json";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_welcome);
new ParseJsonServer().execute();
}
private class ParseJsonServer extends AsyncTask<Void, Void, String> {
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
String resultJsonServer = "";
@Override
protected String doInBackground(Void... params) {
// получаем данные с внешнего ресурса
try {
URL url = new URL(urlServerJson);
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line);
}
resultJsonServer = buffer.toString();
} catch (Exception e) {
e.printStackTrace();
}
return resultJsonServer;
}
@Override
protected void onPostExecute(String strJson) {
if (resultJsonServer != "") {
urlsFromServer = GetListUrlCovers(resultJsonServer);
} else {
CheckListFile(fileNamePath);
if (!CheckFileStorage) {
Toast toast = Toast.makeText(getApplicationContext(),
getString(R.string.NoInternetText), Toast.LENGTH_LONG);
toast.show();
NextActivity();
} else {
NextActivity();
}
}
CheckListFile(fileNamePath);
if (CheckFileStorage) {
String jsResult = MyJSON.getData(getApplicationContext(), fileNamePath);
filesPath = getFilesPathFromFile(jsResult);
} else {
filesPath = new ArrayList<>();
for (int i = 0; i < urlsFromServer.size(); i++) {
int d = i + 1;
String fileUrl = urlsFromServer.get(i);
String filenam = getApplicationContext().getFilesDir() + File.separator + "bookcover_" + d + ".jpg";
FileLoader(fileUrl, filenam);
}
String strJs = new Gson().toJson(filesPath);
if (!checkPermissions()) {
// Toast.makeText(WelcomeActivity.this, "Разрешения уже получены", Toast.LENGTH_SHORT).show();
setPermissions();
}
MyJSON.saveData(getApplicationContext(), strJs, fileNamePath);
}
if (filesPath.size() == urlsFromServer.size()) {
NextActivity();
} else {
try {
deleteFile(fileNamePath);
} catch (Exception e) {
e.printStackTrace();
}
for (int i = 0; i < urlsFromServer.size(); i++) {
int d = i + 1;
String fileUrl = urlsFromServer.get(i);
String filenam = getApplicationContext().getFilesDir() + File.separator + "bookcover_" + d + ".jpg";
FileLoader(fileUrl, filenam);
}
String strJs = new Gson().toJson(filesPath);
if (!checkPermissions()) {
setPermissions();
// Toast.makeText(WelcomeActivity.this, "Разрешения уже получены", Toast.LENGTH_SHORT).show();
}
/*
else {
setPermissions();
}
*/
MyJSON.saveData(getApplicationContext(), strJs, fileNamePath);
NextActivity();
}
}
}
private ArrayList<String> GetListUrlCovers(String strJson) {
JSONObject dataJsonObj;
try {
dataJsonObj = new JSONObject(strJson);
JSONArray books = dataJsonObj.getJSONArray("books");
for (int i = 0; i < books.length(); i++) {
JSONObject book = books.getJSONObject(i);
String url_book = book.getString("coverUrl");
urlsFromServer.add(url_book);// пишу урлы в ArrayList
}
} catch (JSONException e) {
e.printStackTrace();
}
return urlsFromServer;
}
private void CheckListFile(String fileNameStorage) {
File fileUrls = new File(getApplicationContext().getFilesDir().getPath() + "/" + fileNameStorage);
if (fileUrls.exists()) {
CheckFileStorage = true;
}
}
private void FileLoader(String fileUrl, String filename) {
if (!checkPermissions()) {
setPermissions();
// Toast.makeText(WelcomeActivity.this, "Разрешения уже получены", Toast.LENGTH_SHORT).show();
}
/*
else {
setPermissions();
}
*/
ThinDownloadManager downloadManager = new ThinDownloadManager(5); //количество потоков загрузки
Uri downloadUri = Uri.parse(fileUrl);
Uri destinationUri = Uri.parse(filename);
DownloadRequest downloadRequest = new DownloadRequest(downloadUri).setDestinationURI(destinationUri);
downloadManager.add(downloadRequest);
filesPath.add(destinationUri);
}
private ArrayList<Uri> getFilesPathFromFile(String jsResult) {
ArrayList<Uri> urisImg = new ArrayList<>();
try {
JSONArray rootJson = new JSONArray(new JSONTokener(jsResult));
for (int i = 0; i < rootJson.length(); i++) {
JSONObject o = rootJson.getJSONObject(i);
String strTo = (String) o.get("uriString");
urisImg.add(Uri.parse(strTo));
}
} catch (JSONException e) {
e.printStackTrace();
}
return urisImg;
}
private void NextActivity() {
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
Intent intent = new Intent(WelcomeActivity.this, MainActivity.class);
startActivity(intent);
finish();
}
}, 2000);
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
if (requestCode != MY_PERMISSIONS_REQUEST_CODE) {
return;
}
boolean isGranted = true;
for (int result : grantResults) {
if (result != PackageManager.PERMISSION_GRANTED) {
isGranted = false;
break;
}
}
if (isGranted) {
Toast.makeText(WelcomeActivity.this, "Разрешения получены", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(this, "В разрешениях отказано", Toast.LENGTH_LONG).show();
}
}
private boolean checkPermissions() {
if (ActivityCompat.checkSelfPermission(this,
Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
return false;
}
return true;
}
private void setPermissions() {
ActivityCompat.requestPermissions(this, new String[]{
Manifest.permission.WRITE_EXTERNAL_STORAGE}, MY_PERMISSIONS_REQUEST_CODE);
}
}
WelcomeActivity在 课堂上onCreate写如果您使用支持库 - AppCompatActivity 并使用它，则无需检查 api。也可以不检查是否已经有权限，即 checkSelfPermission 方法可以省略。请求许可，如果之前已经获得过，不会有什么不好的事情发生。
接下来，在 WelcomeActivity 类中，添加这个方法
失败时调用的 Toast 会很快消失（他们将没有时间阅读它），因为。随后是第二次请求许可。所以这个实现不是很漂亮。但是你必须明白，在获得许可后，必须从这里调用所需的代码。
一般来说，最好阅读文档，即使使用谷歌翻译，那里的一切都非常清楚。