Prometheus Prometheus - 3 years ago 186
Java Question

Requesting Runtime Permissions Causes Crash

The main reason I'm posting here is that I'm currently stuck without a computer that can run an emulator, I've been having to send the APK to my phone to test it. Even if my phone's connected to my computer, or I have a third party emulator running, it wont work. Due to this...I have no error logs.

The app is a simple password manager, and all the other functions thus far work. I was trying to add an export function, I can't get either to actually write anything. I've checked other questions and various sources online, but I cannot seem to figure out what could be causing it. When the method is called, it simply doesn't do anything as far as I can tell. I apologize if I'm missing something, or if there was indeed another question with the same issue. I couldn't find anything missing.

Here is the method I'm using;

EDIT: The code has been updated to reflect a better method of requesting runtime permissions, which was suggested here. This ultimately is what fixed the application.

//Method017: Exports the account info to a .txt file.
public void exportData() throws IOException {

//Opens dialog to request permission.
ActivityCompat.requestPermissions(Main.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
}

//Method to handle result of permission request.
@Override
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
switch (requestCode) {
case 1: {

// If request is cancelled, the result arrays are empty.
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

//Attempt to write a file to the Download folder.
String content = "hello world";
File file;
FileOutputStream outputStream;
try {
file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), "MyCache");

outputStream = new FileOutputStream(file);
outputStream.write(content.getBytes());
outputStream.close();

//According to an online source, this is necessary to make the file viewable on the device.
Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
intent.setData(Uri.fromFile(file));
sendBroadcast(intent);
} catch (IOException e) {
e.printStackTrace();
}

} else {

// permission denied, boo! Disable the
// functionality that depends on this permission.
Toast.makeText(Main.this, "Permission denied to read your External storage", Toast.LENGTH_SHORT).show();
}
return;
}

// other 'case' lines to check for other
// permissions this app might request
}
}


And my manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.brand.psync">

<application

android:allowBackup="true"
android:icon="@drawable/psynclogo"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme"
android:screenOrientation="portrait">
<activity android:name=".Main">
<intent-filter>
<action
android:name="android.intent.action.MAIN"
android:screenOrientation="portrait" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<category
android:name="android.intent.category.LAUNCHER"
android:screenOrientation="portrait" />
</intent-filter>
</activity>
</application>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
</manifest>


Sorry about the lack of error log...but if I had that, I likely wouldn't need to post here.

Answer Source

I have try your code and it working.

public class SaveFileSampleActivity extends Activity {

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

        TextView lblBackground = new TextView(this);
        lblBackground.setBackgroundColor(Color.WHITE);
        setContentView(lblBackground);

        ActivityCompat.requestPermissions(SaveFileSampleActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
    }


    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case 1: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                    //Attempt to write a file to the Download folder.
                    String content = "hello world";
                    File file;
                    FileOutputStream outputStream;
                    try {
                        file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), "MyCache");

                        outputStream = new FileOutputStream(file);
                        outputStream.write(content.getBytes());
                        outputStream.close();

                        //According to an online source, this is necessary to make the file viewable on the device.
                        Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
                        intent.setData(Uri.fromFile(file));
                        sendBroadcast(intent);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                } else {

                    // permission denied, boo! Disable the
                    // functionality that depends on this permission.
                    Toast.makeText(SaveFileSampleActivity.this, "Permission denied to read your External storage", Toast.LENGTH_SHORT).show();
                }
                return;
            }
            // other 'case' lines to check for other
            // permissions this app might request
        }
    }
}

And mainifest

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity
        android:name=".SaveFileSampleActivity"
        android:label="@string/app_name"
        android:theme="@style/AppTheme.NoActionBar">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

It's work and result: enter image description here

You can review your code. I hope it can help you!

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