如何在phonestatelistener中创建Android AlertDialog？

Question

The code looks like this:

1) Declare the new activity in manifest file. (AndroidManifest.xml):

    <activity
        android:name=".ConfirmDialog"
        android:label="@string/app_name"
        android:theme="@android:style/Theme.Dialog"
        android:launchMode="singleTask"
        android:screenOrientation="vertical">          
    </activity>

2) Create new class extends activity. (public class ConfirmDialog extends Activity)

private static final int DIALOG_YES_NO_MESSAGE = 1;

@Override
protected Dialog onCreateDialog(int id) {
    switch (id) {
    case DIALOG_YES_NO_MESSAGE:
        return new AlertDialog.Builder(ConfirmDialog.this)
            .setIconAttribute(android.R.attr.alertDialogIcon)
            .setTitle(R.string.app_name)
            .setMessage(R.string.ask_confirm)
            .setPositiveButton(R.string.ask_confirm_yes, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int whichButton) {
                    dialog.cancel();
                    finish();
                }
            })
            .setNegativeButton(R.string.ask_confirm_no, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int whichButton) {
                    dialog.cancel();
                    finish();
                }
            })
            .create();
    }
    return null;
}

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

3) Use the new created activity in phonestatelistener. (public class Listener extends PhoneStateListener)

public void onCallStateChanged(int state, String incomingNumber){

    switch(state){              
        case TelephonyManager.CALL_STATE_OFFHOOK:
            confirmCall();          
        break;
    }

    super.onCallStateChanged(state, incomingNumber);

}   

private void confirmCall(){
    Intent intent = new Intent();
    intent.setComponent(new ComponentName("com.example", "com.example.ConfirmDialog"));
    mContext.startActivity(intent);
}

Answer 1

Not all Context objects are equal, and reusing them is dangerous because it can result in the error that you're seeing. Per your comment, your revised code is storing a Context from SherlockFragmentActivity in your Config class, and then using it later when that Activity (and the window that it was using) may not exist anymore. The Context isn't null and can probably be used to do a Toast , but doing windowing operations is very risky.

One solution is to create a dialog-themed activity in your app that will only show the dialog. In confirmCall() , launch your activity with startActivity() , and then let the activity create the dialog. To the user, a dialog will appear on the screen without an app running, but in fact your app is running and can respond to the user's Yes/No choice on the dialog. Be sure to use

new AlertDialog.Builder(this)

so that the dialog's Context is an Activity .