将事件传递回对话框的宿主
当用户触摸对话框的某个操作按钮或从列表中选择某一项时,您的 DialogFragment 可能会自行执行必要的操作,但通常您想将事件传递给打开该对话框的 Activity 或片段。 为此,请定义一个界面,为每种点击事件定义一种方法。然后在从该对话框接收操作事件的宿主组件中实现该界面。
/*对话框的宿主 Activity 会通过对话框片段的构造函数创建一个对话框实例,并通过实现的 NoticeDialogListener 界面接收对话框的事件:*/
public class MainActivity extends FragmentActivity
implements NoticeDialogFragment.NoticeDialogListener{
...
public void showNoticeDialog() {
// Create an instance of the dialog fragment and show it
//显示对话框
DialogFragment dialog = new NoticeDialogFragment();
dialog.show(getSupportFragmentManager(), "NoticeDialogFragment");
//第二个参数是系统用于保存片段状态并在必要时进行恢复的唯一标记名称。
// 该标记还允许您通过调用 findFragmentByTag() 获取片段的句柄。
}
// The dialog fragment receives a reference to this Activity through the
// Fragment.onAttach() callback, which it uses to call the following methods
// defined by the NoticeDialogFragment.NoticeDialogListener interface
@Override
public void onDialogPositiveClick(DialogFragment dialog) {
// User touched the dialog's positive button
...
}
@Override
public void onDialogNegativeClick(DialogFragment dialog) {
// User touched the dialog's negative button
...
}
}
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");
}
}
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
// Build the dialog and set up the button click handlers
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) {
// Send the positive button event back to the host activity
mListener.onDialogPositiveClick(NoticeDialogFragment.this);
}
})
.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
// Send the negative button event back to the host activity
mListener.onDialogNegativeClick(NoticeDialogFragment.this);
}
});
return builder.create();
}
}