android Dialogs

1.引言

Dialog是對話框的基類，可以實現以下子類：

AlertDialog,DatePickerDialog,TimPickerDialog。

這些類為你定義了樣式和結構，不過你可以使用DialogFragment作為對話框的內容。通過DialogFragment你可以自由控制你的對話框，而不是繼承Dialog對象沿用Dialog對象的一些方法。

當用戶按返回鍵或屏幕翻轉的時候要注意DialogFragment的生命周期。DialogFragment也允許你把它的UI用在打的UI上。

如果使用Support library記得引用android.support.v4.app.DialogFragment而不是android.app.DialogFragment.

2.一個最簡單的例子

public class FireMissilesDialogFragment extends DialogFragment {
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        // Use the Builder class for convenient dialog construction
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setMessage(R.string.dialog_fire_missiles)
               .setPositiveButton(R.string.fire, new DialogInterface.OnClickListener() {
                   public void onClick(DialogInterface dialog, int id) {
                       // FIRE ZE MISSILES!
                   }
               })
               .setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
                   public void onClick(DialogInterface dialog, int id) {
                       // User cancelled the dialog
                   }
               });
        // Create the AlertDialog object and return it
        return builder.create();
    }
}

當你想顯示Dialog時，只需調用show()

3.方法回調

在DialogFragment中設置一個interface,通過這個接口可以將事件傳遞到主activity中

public class NoticeDialogFragment extends DialogFragment {
    
    /* The activity that creates an instance of this dialog fragment must
     * implement this interface in order to receive event callbacks.
     * Each method passes the DialogFragment in case the host needs to query it. */
    public interface NoticeDialogListener {
        public void onDialogPositiveClick(DialogFragment dialog);
        public void onDialogNegativeClick(DialogFragment dialog);
    }
    
    // Use this instance of the interface to deliver action events
    NoticeDialogListener mListener;
    
    // Override the Fragment.onAttach() method to instantiate the NoticeDialogListener
    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        // Verify that the host activity implements the callback interface
        try {
            // Instantiate the NoticeDialogListener so we can send events to the host
            mListener = (NoticeDialogListener) activity;
        } catch (ClassCastException e) {
            // The activity doesn't implement the interface, throw exception
            throw new ClassCastException(activity.toString()
                    + " must implement NoticeDialogListener");
        }
    }
    ...
}

4.DialogFragmnt既可以顯示為一個全屏的對話框，亦可以顯示為一個嵌入的Fragment

public class CustomDialogFragment extends DialogFragment {
    /** The system calls this to get the DialogFragment's layout, regardless
        of whether it's being displayed as a dialog or an embedded fragment. */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the layout to use as dialog or embedded fragment
        return inflater.inflate(R.layout.purchase_items, container, false);
    }
  
    /** The system calls this only when creating the layout in a dialog. */
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        // The only reason you might override this method when using onCreateView() is
        // to modify any dialog characteristics. For example, the dialog includes a
        // title by default, but your custom layout might not need it. So here you can
        // remove the dialog title, but you must call the superclass to get the Dialog.
        Dialog dialog = super.onCreateDialog(savedInstanceState);
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        return dialog;
    }
}

public void showDialog() {
    FragmentManager fragmentManager = getSupportFragmentManager();
    CustomDialogFragment newFragment = new CustomDialogFragment();
    
    if (mIsLargeLayout) {
        // The device is using a large layout, so show the fragment as a dialog
        newFragment.show(fragmentManager, "dialog");
    } else {
        // The device is smaller, so show the fragment fullscreen
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        // For a little polish, specify a transition animation
        transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        // To make it fullscreen, use the 'content' root view as the container
        // for the fragment, which is always the root view for the activity
        transaction.add(android.R.id.content, newFragment)
                   .addToBackStack(null).commit();
    }
}

其中mIsLargeLayout根據當前設備判斷是否使用app的大UI布局。

mIsLargeLayout的取值方法如下：

res/values/bools.xml

    false

res/values-large/bools.xml

    true

boolean mIsLargeLayout;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mIsLargeLayout = getResources().getBoolean(R.bool.large_layout);
}

5.如果你的應用只是適配了小屏幕的手機，那麼：

將你的activity設置為Theme.Holo.DialogWhenLarge會在大屏幕上展示為對話框。