对话框

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对话框是提示用户做出决定或输入更多信息的小窗口。对话框不会填满屏幕,通常用于需要用户执行操作才能继续的模态事件。

显示基本对话框的图片
图 1.一个基本对话框。

Dialog 类是对话框的基类,但不直接实例化 Dialog,而是应使用下列子类之一:

AlertDialog
此对话框可显示标题、最多三个按钮、可选项目列表或自定义布局。
DatePickerDialogTimePickerDialog
一个对话框,带有可让用户选择日期或时间的预定义界面。

这些类用于定义对话框的样式和结构。您还需要一个 DialogFragment 作为对话框的容器。DialogFragment 类提供了创建对话框和管理其外观所需的所有控件,而不是对 Dialog 对象调用方法。

使用 DialogFragment 管理对话框可以正确处理生命周期事件,例如当用户点按返回按钮或旋转屏幕时。借助 DialogFragment 类,您还可以将对话框的界面作为可嵌入组件在较大界面中重复使用(就像传统的 Fragment 一样),例如当您想让对话框界面在大屏幕和小屏幕上具有不同外观时。

本文档的以下部分介绍了如何将 DialogFragmentAlertDialog 对象结合使用。如果您想创建日期或时间选择器,请阅读向应用添加选择器

创建对话框 fragment

您可以通过扩展 DialogFragment 并在 onCreateDialog() 回调方法中创建 AlertDialog 来实现各种对话框设计,包括自定义布局和 Material Design 对话框中介绍的布局。

例如,以下是在 DialogFragment 内管理的基本 AlertDialog

Kotlin

class StartGameDialogFragment : DialogFragment() {
    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        return activity?.let {
            // Use the Builder class for convenient dialog construction.
            val builder = AlertDialog.Builder(it)
            builder.setMessage("Start game")
                .setPositiveButton("Start") { dialog, id ->
                    // START THE GAME!
                }
                .setNegativeButton("Cancel") { dialog, id ->
                    // User cancelled the dialog.
                }
            // Create the AlertDialog object and return it.
            builder.create()
        } ?: throw IllegalStateException("Activity cannot be null")
    }
}

class OldXmlActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_old_xml)

        StartGameDialogFragment().show(supportFragmentManager, "GAME_DIALOG")
    }
}

Java

public class StartGameDialogFragment 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_start_game)
               .setPositiveButton(R.string.start, new DialogInterface.OnClickListener() {
                   public void onClick(DialogInterface dialog, int id) {
                       // START THE GAME!
                   }
               })
               .setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
                   public void onClick(DialogInterface dialog, int id) {
                       // User cancels the dialog.
                   }
               });
        // Create the AlertDialog object and return it.
        return builder.create();
    }
}
// ...

StartGameDialogFragment().show(supportFragmentManager, "GAME_DIALOG");

当您创建此类的实例并对该对象调用 show() 时,对话框将如下图所示。

一张图片,显示包含两个操作按钮的基本对话框
图 2. 一个包含一条消息和两个操作按钮的对话框。

下一部分将详细介绍如何使用 AlertDialog.Builder API 创建对话框。

根据对话框的复杂程度,您可以在 DialogFragment 中实现各种其他回调方法,包括所有基本的 fragment 生命周期方法

构建提醒对话框

借助 AlertDialog 类,您可以构建各种对话框设计,并且这通常是您需要的唯一对话框类。如下图所示,提醒对话框有三个区域:

  • Title:可选,仅当详细消息、列表或自定义布局占据内容区域时使用。如果您需要陈述简单的消息或问题,则不需要标题。
  • 内容区域:此区域可以显示消息、列表或其他自定义布局。
  • 操作按钮:一个对话框中最多可以有三个操作按钮。

AlertDialog.Builder 类提供的 API 可让您创建包含这些类型的内容(包括自定义布局)的 AlertDialog

如需构建 AlertDialog,请执行以下操作:

Kotlin

val builder: AlertDialog.Builder = AlertDialog.Builder(context)
builder
    .setMessage("I am the message")
    .setTitle("I am the title")

val dialog: AlertDialog = builder.create()
dialog.show()

Java

// 1. Instantiate an AlertDialog.Builder with its constructor.
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());

// 2. Chain together various setter methods to set the dialog characteristics.
builder.setMessage(R.string.dialog_message)
       .setTitle(R.string.dialog_title);

// 3. Get the AlertDialog.
AlertDialog dialog = builder.create();

上面的代码段会生成以下对话框:

图片显示了一个对话框,其中包含标题、内容区域和两个操作按钮。
图 3. 基本提醒对话框的布局。

添加按钮

如需添加如图 2 所示的操作按钮,请调用 setPositiveButton()setNegativeButton() 方法:

Kotlin

val builder: AlertDialog.Builder = AlertDialog.Builder(context)
builder
    .setMessage("I am the message")
    .setTitle("I am the title")
    .setPositiveButton("Positive") { dialog, which ->
        // Do something.
    }
    .setNegativeButton("Negative") { dialog, which ->
        // Do something else.
    }

val dialog: AlertDialog = builder.create()
dialog.show()

Java

AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
// Add the buttons.
builder.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
           public void onClick(DialogInterface dialog, int id) {
               // User taps OK button.
           }
       });
builder.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
           public void onClick(DialogInterface dialog, int id) {
               // User cancels the dialog.
           }
       });
// Set other dialog properties.
...

// Create the AlertDialog.
AlertDialog dialog = builder.create();

set...Button() 方法需要按钮的标题(由字符串资源提供)以及 DialogInterface.OnClickListener(用于定义用户点按该按钮时执行的操作)。

您可以添加三个操作按钮:

  • 肯定:使用此字段表示接受并继续执行操作(“确定”操作)。
  • 否定匹配:使用此字段可取消操作。
  • 中性:当用户可能不想继续执行操作但也不一定想要取消时,请使用此选项。它显示在肯定按钮和否定按钮之间。例如,操作可能是“以后再提醒我”。

对于每种按钮类型,您只能为 AlertDialog 添加一个该类型的按钮。例如,您不能有多个“肯定”按钮。

前面的代码段为您提供了如下所示的提醒对话框:

图片:显示提醒对话框,其中包含标题、消息和两个操作按钮。
图 4. 一个提醒对话框,其中包含标题、消息和两个操作按钮。

添加列表

AlertDialog API 提供三种类型的列表:

  • 传统的单选列表。
  • 永久性单选列表(单选按钮)。
  • 永久性多选列表(复选框)。

如需创建如图 5 所示的单选列表,请使用 setItems() 方法:


Kotlin

val builder: AlertDialog.Builder = AlertDialog.Builder(context)
builder
    .setTitle("I am the title")
    .setPositiveButton("Positive") { dialog, which ->
        // Do something.
    }
    .setNegativeButton("Negative") { dialog, which ->
        // Do something else.
    }
    .setItems(arrayOf("Item One", "Item Two", "Item Three")) { dialog, which ->
        // Do something on item tapped.
    }

val dialog: AlertDialog = builder.create()
dialog.show()

Java

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    builder.setTitle(R.string.pick_color)
           .setItems(R.array.colors_array, new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int which) {
               // The 'which' argument contains the index position of the selected item.
           }
    });
    return builder.create();
}

以下代码段会生成如下所示的对话框:

一张图片,显示了一个包含标题和列表的对话框。
图 5. 一个包含标题和列表的对话框。

由于列表显示在对话框的内容区域中,因此对话框无法同时显示消息和列表。使用 setTitle() 为对话框设置标题。如需为列表指定项,请调用 setItems() 并传递数组。或者,您也可以使用 setAdapter() 指定列表。这样,您就可以使用 ListAdapter 以动态数据(如来自数据库的数据)支持列表。

如果您使用 ListAdapter 支持列表,请始终使用 Loader,以便内容异步加载。使用适配器构建布局加载器中对此进行了详细说明。

添加永久性多选或单选列表

如需添加多选(复选框)或单选(单选按钮)列表,请分别使用 setMultiChoiceItems()setSingleChoiceItems() 方法。

例如,以下代码段展示了如何创建如图 6 所示的多选列表,将选定项保存在 ArrayList 中:

Kotlin

val builder: AlertDialog.Builder = AlertDialog.Builder(context)
builder
    .setTitle("I am the title")
    .setPositiveButton("Positive") { dialog, which ->
        // Do something.
    }
    .setNegativeButton("Negative") { dialog, which ->
        // Do something else.
    }
    .setMultiChoiceItems(
        arrayOf("Item One", "Item Two", "Item Three"), null) { dialog, which, isChecked ->
        // Do something.
    }

val dialog: AlertDialog = builder.create()
dialog.show()

Java

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    selectedItems = new ArrayList();  // Where we track the selected items
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    // Set the dialog title.
    builder.setTitle(R.string.pick_toppings)
    // Specify the list array, the items to be selected by default (null for
    // none), and the listener through which to receive callbacks when items
    // are selected.
           .setMultiChoiceItems(R.array.toppings, null,
                      new DialogInterface.OnMultiChoiceClickListener() {
               @Override
               public void onClick(DialogInterface dialog, int which,
                       boolean isChecked) {
                   if (isChecked) {
                       // If the user checks the item, add it to the selected
                       // items.
                       selectedItems.add(which);
                   } else if (selectedItems.contains(which)) {
                       // If the item is already in the array, remove it.
                       selectedItems.remove(which);
                   }
               }
           })
    // Set the action buttons
           .setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
               @Override
               public void onClick(DialogInterface dialog, int id) {
                   // User taps OK, so save the selectedItems results
                   // somewhere or return them to the component that opens the
                   // dialog.
                   ...
               }
           })
           .setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
               @Override
               public void onClick(DialogInterface dialog, int id) {
                   ...
               }
           });

    return builder.create();
}
此图片显示了一个包含多选列表的对话框。
图 6. 单选题列表。

您可以通过以下方式获取单选提醒对话框:

Kotlin

val builder: AlertDialog.Builder = AlertDialog.Builder(context)
builder
    .setTitle("I am the title")
    .setPositiveButton("Positive") { dialog, which ->
        // Do something.
    }
    .setNegativeButton("Negative") { dialog, which ->
        // Do something else.
    }
    .setSingleChoiceItems(
        arrayOf("Item One", "Item Two", "Item Three"), 0
    ) { dialog, which ->
        // Do something.
    }

val dialog: AlertDialog = builder.create()
dialog.show()

Java

        String[] choices = {"Item One", "Item Two", "Item Three"};
        
        AlertDialog.Builder builder = AlertDialog.Builder(context);
        builder
                .setTitle("I am the title")
                .setPositiveButton("Positive", (dialog, which) -> {

                })
                .setNegativeButton("Negative", (dialog, which) -> {

                })
                .setSingleChoiceItems(choices, 0, (dialog, which) -> {

                });

        AlertDialog dialog = builder.create();
        dialog.show();

这会生成以下示例:

此图片显示了一个包含单选列表的对话框。
图 7. 单选列表。

创建自定义布局

如果您希望在对话框中使用自定义布局,请创建布局,然后通过对 AlertDialog.Builder 对象调用 setView() 来将其添加到 AlertDialog

显示自定义对话框布局的图片。
图 8. 自定义对话框布局。

默认情况下,自定义布局会填充对话框窗口,但您仍然可以使用 AlertDialog.Builder 方法添加按钮和标题。

例如,以下是上述自定义对话框布局的布局文件:

res/layout/dialog_signin.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">
    <ImageView
        android:src="@drawable/header_logo"
        android:layout_width="match_parent"
        android:layout_height="64dp"
        android:scaleType="center"
        android:background="#FFFFBB33"
        android:contentDescription="@string/app_name" />
    <EditText
        android:id="@+id/username"
        android:inputType="textEmailAddress"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:layout_marginLeft="4dp"
        android:layout_marginRight="4dp"
        android:layout_marginBottom="4dp"
        android:hint="@string/username" />
    <EditText
        android:id="@+id/password"
        android:inputType="textPassword"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="4dp"
        android:layout_marginLeft="4dp"
        android:layout_marginRight="4dp"
        android:layout_marginBottom="16dp"
        android:fontFamily="sans-serif"
        android:hint="@string/password"/>
</LinearLayout>

如需膨胀 DialogFragment 中的布局,请使用 getLayoutInflater() 获取 LayoutInflater 并调用 inflate()。 第一个参数是布局资源 ID,第二个参数是布局的父视图。然后,您可以调用 setView() 来将布局放入对话框中。详见下例。

Kotlin

override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    return activity?.let {
        val builder = AlertDialog.Builder(it)
        // Get the layout inflater.
        val inflater = requireActivity().layoutInflater;

        // Inflate and set the layout for the dialog.
        // Pass null as the parent view because it's going in the dialog
        // layout.
        builder.setView(inflater.inflate(R.layout.dialog_signin, null))
                // Add action buttons.
                .setPositiveButton(R.string.signin,
                        DialogInterface.OnClickListener { dialog, id ->
                            // Sign in the user.
                        })
                .setNegativeButton(R.string.cancel,
                        DialogInterface.OnClickListener { dialog, id ->
                            getDialog().cancel()
                        })
        builder.create()
    } ?: throw IllegalStateException("Activity cannot be null")
}

Java

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    // Get the layout inflater.
    LayoutInflater inflater = requireActivity().getLayoutInflater();

    // Inflate and set the layout for the dialog.
    // Pass null as the parent view because it's going in the dialog layout.
    builder.setView(inflater.inflate(R.layout.dialog_signin, null))
    // Add action buttons
           .setPositiveButton(R.string.signin, new DialogInterface.OnClickListener() {
               @Override
               public void onClick(DialogInterface dialog, int id) {
                   // Sign in the user.
               }
           })
           .setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {
                   LoginDialogFragment.this.getDialog().cancel();
               }
           });
    return builder.create();
}

如果您需要自定义对话框,可以改为将 Activity 显示为对话框,而不是使用 Dialog API。创建一个 activity,并在 <activity> 清单元素中将其主题背景设置为 Theme.Holo.Dialog

<activity android:theme="@android:style/Theme.Holo.Dialog" >

Activity 现在会显示在一个对话框窗口中,而非全屏显示。

将事件传递回对话框的宿主

当用户点按对话框的某个操作按钮或从列表中选择某个项时,您的 DialogFragment 可能会自行执行必要的操作,但通常情况下您需要将事件传递给打开该对话框的 activity 或 fragment。为此,请定义一个接口,为每种点击事件定义一个方法。然后,在从对话框接收操作事件的主机组件中实现该接口。

例如,以下 DialogFragment 定义了一个接口,通过该接口将事件传回给宿主 activity:

Kotlin

class NoticeDialogFragment : DialogFragment() {
    // Use this instance of the interface to deliver action events.
    internal lateinit var listener: NoticeDialogListener

    // The activity that creates an instance of this dialog fragment must
    // implement this interface to receive event callbacks. Each method passes
    // the DialogFragment in case the host needs to query it.
    interface NoticeDialogListener {
        fun onDialogPositiveClick(dialog: DialogFragment)
        fun onDialogNegativeClick(dialog: DialogFragment)
    }

    // Override the Fragment.onAttach() method to instantiate the
    // NoticeDialogListener.
    override fun onAttach(context: Context) {
        super.onAttach(context)
        // Verify that the host activity implements the callback interface.
        try {
            // Instantiate the NoticeDialogListener so you can send events to
            // the host.
            listener = context as NoticeDialogListener
        } catch (e: ClassCastException) {
            // The activity doesn't implement the interface. Throw exception.
            throw ClassCastException((context.toString() +
                    " must implement NoticeDialogListener"))
        }
    }
}

Java

public class NoticeDialogFragment extends DialogFragment {

    // The activity that creates an instance of this dialog fragment must
    // implement this interface 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 listener;

    // Override the Fragment.onAttach() method to instantiate the
    // NoticeDialogListener.
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        // Verify that the host activity implements the callback interface.
        try {
            // Instantiate the NoticeDialogListener so you can send events to
            // the host.
            listener = (NoticeDialogListener) context;
        } catch (ClassCastException e) {
            // The activity doesn't implement the interface. Throw exception.
            throw new ClassCastException(activity.toString()
                    + " must implement NoticeDialogListener");
        }
    }
    ...
}

托管对话框的 activity 会使用对话框 fragment 的构造函数创建对话框实例,并通过 NoticeDialogListener 接口的实现接收对话框的事件:

Kotlin

class MainActivity : FragmentActivity(),
        NoticeDialogFragment.NoticeDialogListener {

    fun showNoticeDialog() {
        // Create an instance of the dialog fragment and show it.
        val dialog = NoticeDialogFragment()
        dialog.show(supportFragmentManager, "NoticeDialogFragment")
    }

    // 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 fun onDialogPositiveClick(dialog: DialogFragment) {
        // User taps the dialog's positive button.
    }

    override fun onDialogNegativeClick(dialog: DialogFragment) {
        // User taps the dialog's negative button.
    }
}

Java

public class MainActivity extends FragmentActivity
                          implements NoticeDialogFragment.NoticeDialogListener{
    ...
    public void showNoticeDialog() {
        // Create an instance of the dialog fragment and show it.
        DialogFragment dialog = new NoticeDialogFragment();
        dialog.show(getSupportFragmentManager(), "NoticeDialogFragment");
    }

    // 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 taps the dialog's positive button.
        ...
    }

    @Override
    public void onDialogNegativeClick(DialogFragment dialog) {
        // User taps the dialog's negative button.
        ...
    }
}

由于宿主 activity 会实现 NoticeDialogListener(由上例中显示的 onAttach() 回调方法强制执行),因此对话框 fragment 可以使用接口回调方法向 activity 传递点击事件:

Kotlin

    override fun onCreateDialog(savedInstanceState: Bundle): Dialog {
        return activity?.let {
            // Build the dialog and set up the button click handlers.
            val builder = AlertDialog.Builder(it)

            builder.setMessage(R.string.dialog_start_game)
                    .setPositiveButton(R.string.start,
                            DialogInterface.OnClickListener { dialog, id ->
                                // Send the positive button event back to the
                                // host activity.
                                listener.onDialogPositiveClick(this)
                            })
                    .setNegativeButton(R.string.cancel,
                            DialogInterface.OnClickListener { dialog, id ->
                                // Send the negative button event back to the
                                // host activity.
                                listener.onDialogNegativeClick(this)
                            })

            builder.create()
        } ?: throw IllegalStateException("Activity cannot be null")
    }

Java

public class NoticeDialogFragment extends DialogFragment {
    ...
    @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_start_game)
               .setPositiveButton(R.string.start, new DialogInterface.OnClickListener() {
                   public void onClick(DialogInterface dialog, int id) {
                       // Send the positive button event back to the host activity.
                       listener.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.
                       listener.onDialogNegativeClick(NoticeDialogFragment.this);
                   }
               });
        return builder.create();
    }
}

显示对话框

如果要显示对话框,请创建 DialogFragment 的实例并调用 show(),并传递对话框 fragment 的 FragmentManager 和标记名称。

您可以通过从 FragmentActivity 调用 getSupportFragmentManager() 或从 Fragment 调用 getParentFragmentManager() 来获取 FragmentManager。请参阅以下示例:

Kotlin

fun confirmStartGame() {
    val newFragment = StartGameDialogFragment()
    newFragment.show(supportFragmentManager, "game")
}

Java

public void confirmStartGame() {
    DialogFragment newFragment = new StartGameDialogFragment();
    newFragment.show(getSupportFragmentManager(), "game");
}

第二个参数 "game" 是系统用于保存 fragment 状态并在必要时进行恢复的唯一标记名称。利用此标记,您还可以通过调用 findFragmentByTag() 获取 fragment 的句柄。

全屏显示对话框或将其作为嵌入式 Fragment 显示

您可能希望界面设计的一部分在某些情况下显示为对话框,而在其他情况下显示为全屏或嵌入式 fragment。您可能还希望它根据设备的屏幕尺寸显示不同的效果。DialogFragment 类可灵活实现这一点,因为它可以充当可嵌入的 Fragment

但在这种情况下,您不能使用 AlertDialog.Builder 或其他 Dialog 对象来构建对话框。如果您希望 DialogFragment 是可嵌入的,请在布局中定义对话框的界面,然后在 onCreateView() 回调中加载布局。

以下示例 DialogFragment 可以使用名为 purchase_items.xml 的布局显示为对话框或可嵌入式 fragment:

Kotlin

class CustomDialogFragment : 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 fun onCreateView(
            inflater: LayoutInflater,
            container: ViewGroup?,
            savedInstanceState: Bundle?
    ): View {
        // Inflate the layout to use as a 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 fun onCreateDialog(savedInstanceState: Bundle): Dialog {
        // The only reason you might override this method when using
        // onCreateView() is to modify the dialog characteristics. For example,
        // the dialog includes a title by default, but your custom layout might
        // not need it. Here, you can remove the dialog title, but you must
        // call the superclass to get the Dialog.
        val dialog = super.onCreateDialog(savedInstanceState)
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE)
        return dialog
    }
}

Java

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 a 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 the dialog characteristics. For example,
        // the dialog includes a title by default, but your custom layout might
        // not need it. 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;
    }
}

以下示例根据屏幕尺寸确定是将 fragment 显示为对话框还是全屏界面:

Kotlin

fun showDialog() {
    val fragmentManager = supportFragmentManager
    val newFragment = CustomDialogFragment()
    if (isLargeLayout) {
        // 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.
        val transaction = fragmentManager.beginTransaction()
        // For a polished look, 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()
    }
}

Java

public void showDialog() {
    FragmentManager fragmentManager = getSupportFragmentManager();
    CustomDialogFragment newFragment = new CustomDialogFragment();

    if (isLargeLayout) {
        // 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 polished look, 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();
    }
}

如需详细了解如何执行 fragment 事务,请参阅 fragment

在此示例中,mIsLargeLayout 布尔值指定当前设备是否必须使用应用的大布局设计,从而将此 fragment 显示为对话框而非全屏。设置此类布尔值的最佳方法是声明一个 bool 资源值,其中包含适用于不同屏幕尺寸的备用资源值。例如,以下两个版本的布尔资源适用于不同屏幕尺寸:

res/values/bools.xml

<!-- Default boolean values -->
<resources>
    <bool name="large_layout">false</bool>
</resources>

res/values-large/bools.xml

<!-- Large screen boolean values -->
<resources>
    <bool name="large_layout">true</bool>
</resources>

然后,您可以在 activity 的 onCreate() 方法执行期间初始化 mIsLargeLayout 值,如以下示例所示:

Kotlin

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    isLargeLayout = resources.getBoolean(R.bool.large_layout)
}

Java

boolean isLargeLayout;

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

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

在大屏幕上将 activity 显示为对话框

与在小屏幕上将对话框显示为全屏界面,您可以在大屏幕上将 Activity 显示为对话框来获得相同的结果。您选择的方法取决于应用设计,但如果您的应用是针对小屏幕设计的,并且您希望通过将短期存在的 activity 显示为对话框来改善平板电脑体验,将 activity 显示为对话框往往会很有用。

如需仅在大屏幕上将 activity 显示为对话框,请将 Theme.Holo.DialogWhenLarge 主题应用于 <activity> 清单元素:

<activity android:theme="@android:style/Theme.Holo.DialogWhenLarge" >

如需详细了解如何使用主题设置 activity 的样式,请参阅样式和主题

关闭对话框

当用户点按使用 AlertDialog.Builder 创建的操作按钮时,系统会为您关闭对话框。

系统还会在用户点按对话框列表中的项时关闭对话框,除非列表使用单选按钮或复选框。否则,您也可以通过对 DialogFragment 调用 dismiss() 来手动关闭对话框。

如果您需要在对话框消失时执行某些操作,可以在 DialogFragment 中实现 onDismiss() 方法。

您还可取消对话框。这是一个特殊事件,表示用户未完成任务就离开对话框。如果用户点按“返回”按钮或点按对话框区域以外的屏幕,或者您对 Dialog 明确调用 cancel()(例如为了响应对话框中的“取消”按钮),就会发生这种情况。

如上例所示,您可以通过在 DialogFragment 类中实现 onCancel() 来响应取消事件。