Android：AlertDialog不显示

Question

我刚刚开始学习Android编程，但遇到了问题： My alert dialog's don't show up 。

我的想法：启动应用程序后，它将自动检查设备是否已连接到互联网，并给出建议（通过警报对话框）。

我真的希望有人能找到解决方案，因为我在看很多教程，但是每个地方都以onClickListener （Button）开头的代码

代码段：

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

添加上下文。

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();
}

///////

更改此行：

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

至：

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

Answer 2

我认为这个问题是因为您要求在启动活动上完成！ 为什么您必须完成它，尽管您需要在上下文中显示警报对话框！

检查你的logcat，你会发现这个

YourActivity泄漏了最初在此处添加的窗口com.android.internal.policy.impl.PhoneWindow$DecorView@40704090

您可以删除完成活动..，并将完成活动动作移动为对话框按钮动作之一。

Answer 3

问题在于您正在使用SplashActivity上下文创建AlertDialog ，但是SplashActivity您将完成SplashActivity ，并且AlertDialog所属的上下文不再存在。

考虑到您只想在显示此消息时选择“ Enable ，然后再转到第二个活动MainActivity ， We recommend to use wifi, enable it? 。 您可以执行以下操作：

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();

        }
    }
}

这里有很多选择。 但是重要的是，实际上您正在显示AlertDialog但是却看不到它，因为您正在启动另一个活动并完成SplashActivity ，破坏了AlertDialog首先实例化的上下文（ this ） new AlertDialog.Builder(this); 。