Android：AlertDialog不显示

Question

I just started learning Android programming and got problem : My alert dialog's don't show up .

My idea : When app have been launched, it automatically checks if device is connected to internet, and gives suggestions (By alert dialog's).

I really hope, that some one have solution, because I was looking in many tutorials, but every where was code that starts with onClickListener (Button)

Code Snippet:

public class SplashActivity extends AppCompatActivity {

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

    checkConnection();

    Intent intent = new Intent(this, MainActivity.class);
    startActivity(intent);
    finish();
}


void checkConnection() {
    final ConnectivityManager connMgr = (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
    final android.net.NetworkInfo wifi = connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
    final android.net.NetworkInfo mobile = connMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);

    AlertDialog.Builder connectionAlert = new AlertDialog.Builder(this);

    if (wifi.isConnectedOrConnecting ()) {
        // Do nothing
    } else if (mobile.isConnectedOrConnecting ()) {

        connectionAlert.setMessage("We recommend to use wifi, enable it?");
        connectionAlert.setPositiveButton("Enable", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface arg0, int arg1) {
                Toast.makeText(SplashActivity.this,"Wifi has been enabled!",Toast.LENGTH_LONG).show();
            }
        });

        connectionAlert.setNegativeButton("No",new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                finish();
            }
        });

        connectionAlert.show();

    } else {

        connectionAlert.setMessage("Please, enable internet connection!");
        connectionAlert.setNeutralButton("Wifi", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface arg0, int arg1) {
                Toast.makeText(SplashActivity.this,"Wifi has been enabled!",Toast.LENGTH_LONG).show();
            }
        });

        connectionAlert.setNeutralButton("Mobile Data", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface arg0, int arg1) {
                Toast.makeText(SplashActivity.this,"Mobile Data has been enabled!",Toast.LENGTH_LONG).show();
            }
        });

        connectionAlert.setNegativeButton("No",new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                finish();
            }
        });

        connectionAlert.show();

    }
}

}

Answer 1

Add context.

public class SplashActivity extends AppCompatActivity {

private Context context;

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

    checkConnection();

    Intent intent = new Intent(this, MainActivity.class);
    startActivity(intent);
    finish();
}

///////

Change this line:

AlertDialog.Builder connectionAlert = new AlertDialog.Builder(this); 

To:

AlertDialog.Builder connectionAlert = new AlertDialog.Builder(context);

Answer 2

i think the issue because you call finish on the splash activity ! why you have to finish it although you need to show alert dialog on its context !

check your logcat you will find this

YourActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40704090 that was originally added here

you can remove finish activity .. and move finish activity action to be one of the dialog buttons actions.

Answer 3

The problem is that you are creating an AlertDialog with the SplashActivity context, but you are finishing your SplashActivity right after and the context where the AlertDialog belongs no longer exists.

Considering that you want to move to your second activity, MainActivity , only before you choose Enable when you are showing this message We recommend to use wifi, enable it? . What you can do is something like this:

public class SplashActivity extends AppCompatActivity {

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

        checkConnection();
    }


    void checkConnection() {
        final ConnectivityManager connMgr = (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
        final android.net.NetworkInfo wifi = connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
        final android.net.NetworkInfo mobile = connMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);

        AlertDialog.Builder connectionAlert = new AlertDialog.Builder(this);

        if (wifi.isConnectedOrConnecting()) {
            // Do nothing
        } else if (mobile.isConnectedOrConnecting()) {

            connectionAlert.setMessage("We recommend to use wifi, enable it?");
            connectionAlert.setPositiveButton("Enable", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface arg0, int arg1) {
                    Toast.makeText(SplashActivity.this, "Wifi has been enabled!", Toast.LENGTH_LONG).show();
                    Intent intent = new Intent(SplashActivity.this, MainActivity.class);
                    startActivity(intent);
                    finish();
                }
            });

            connectionAlert.setNegativeButton("No", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    finish();
                }
            });

            connectionAlert.show();

        } else {

            connectionAlert.setMessage("Please, enable internet connection!");
            connectionAlert.setNeutralButton("Wifi", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface arg0, int arg1) {
                    Toast.makeText(SplashActivity.this, "Wifi has been enabled!", Toast.LENGTH_LONG).show();
                }
            });

            connectionAlert.setNeutralButton("Mobile Data", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface arg0, int arg1) {
                    Toast.makeText(SplashActivity.this, "Mobile Data has been enabled!", Toast.LENGTH_LONG).show();
                }
            });

            connectionAlert.setNegativeButton("No", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    finish();
                }
            });

            connectionAlert.show();

        }
    }
}

There are a lot of options here. But the important thing is that actually you are showing the AlertDialog but you are not being able to see it because you are starting another activity and finishing the SplashActivity , destroying the context ( this ) where the AlertDialog was first instantiated new AlertDialog.Builder(this); .