详解Android应用中DialogFragment的基本用法

DialogFragment的基本用法
1. 创建DialogFragment

public class DialogA extends DialogFragment implements DialogInterface.OnClickListener {

 @Override
 public Dialog onCreateDialog(Bundle savedInstanceState) {
  AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
  builder.setMessage(R.string.dialoga_title)
    .setPositiveButton(R.string.ok, this)
    .setNegativeButton(R.string.cancel, this);

  return builder.create();
 } 

 @Override
 public void onClick(DialogInterface dialog, int id) {
  switch(id) {
   case AlertDialog.BUTTON_NEGATIVE:
    Toast.makeText(getActivity(), "Negative", Toast.LENGTH_SHORT).show();
    break;
   case AlertDialog.BUTTON_POSITIVE:
    Toast.makeText(getActivity(), "Positive", Toast.LENGTH_SHORT).show();
    break;
   default:
    break;
  }
 }
}

说明：自定义一个DialogFragment，并重写它的onCreateDialog()方法。
2. 调用该DialogFragment
下面是在FragmentActivity中调用该DialogFragment对话框。

public class DialogTest extends FragmentActivity {

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

  showDialog();
 }

 private void showDialog() {
  FragmentManager fm = getSupportFragmentManager();
  DialogA dialoga = new DialogA();
  dialoga.show(fm, "fragmenta");
 }
}

自定义DialogFragment布局
下面介绍自定义DialogFragment的布局的方法
点击查看：自定义DialogFragment布局的完整代码
1. 设置布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical" >

 <TextView
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:hint="@string/dialoga_intro" />

 <ImageView
  android:id="@+id/image"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:src="@drawable/ic_action_video" />

</LinearLayout>

2. 使用布局

public class DialogA extends DialogFragment implements DialogInterface.OnClickListener {

 @Override
 public Dialog onCreateDialog(Bundle savedInstanceState) {
  AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
  LayoutInflater inflater = getActivity().getLayoutInflater();
  builder.setView(inflater.inflate(R.layout.dialoga, null))
    .setMessage(R.string.dialoga_title)
    .setPositiveButton(R.string.ok, this)
    .setNegativeButton(R.string.cancel, this);

  return builder.create();
 }

 @Override
 public void onClick(DialogInterface dialog, int id) {
  switch(id) {
   case AlertDialog.BUTTON_NEGATIVE:
    Toast.makeText(getActivity(), "Negative", Toast.LENGTH_SHORT).show();
    break;
   case AlertDialog.BUTTON_POSITIVE:
    Toast.makeText(getActivity(), "Positive", Toast.LENGTH_SHORT).show();
    break;
   default:
    break;
  }
 }
}

DialogFragment和Activity的交互
下面介绍自定义DialogFragment和Activity交互的方法
点击查看：DialogFragment和Activity交互的完整代码
1. 定义通信接口
在DialogFragment中定义它们之间的通信接口。

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");
 }
}

2. 在DialogFragment中调用该接口

@Override
public void onClick(DialogInterface dialog, int id) {
 switch(id) {
  case AlertDialog.BUTTON_POSITIVE:
   //Toast.makeText(getActivity(), "Negative", Toast.LENGTH_SHORT).show();
   mListener.onDialogPositiveClick(DialogA.this);
   break;
  case AlertDialog.BUTTON_NEGATIVE:
   //Toast.makeText(getActivity(), "Positive", Toast.LENGTH_SHORT).show();
   mListener.onDialogNegativeClick(DialogA.this);
   break;
  default:
   break;
 }
}

3. 在Activity中实现该接口

public class DialogTest extends FragmentActivity
 implements DialogA.NoticeDialogListener {

 ...

 @Override
 public void onDialogPositiveClick(DialogFragment dialog) {
  Toast.makeText(this, "Positive Callback", Toast.LENGTH_SHORT).show();
 }
 @Override
 public void onDialogNegativeClick(DialogFragment dialog) {
  Toast.makeText(this, "Negative Callback", Toast.LENGTH_SHORT).show();
 }
}

Dialog与DialogFragment的对比
从代码的编写角度看，Dialog使用起来要更为简单，但是Google则是推荐尽量使用DialogFragment（对于Android 3.0以下的版本，可以结合使用support包中提供的DialogFragment以及FragmentActivity）。今天试着用这两种方式来创建对话框，发现DialogFragment果然有一个非常好的特性（在手机配置变化，导致Activity需要重新创建时，例如旋屏，基于DialogFragment的对话框将会由FragmentManager自动重建，然而基于Dialog实现的对话框则没有这样的能力）。

下面是两段实例代码：

他们使用的界面都一样：（dialog.xml）

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical" >

 <ImageView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:src="@drawable/ic_launcher" />

</LinearLayout>

1.基于Dialog实现的对话框

public class MainActivity extends Activity {
 private Button clk;
 private Dialog dialog;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  clk = (Button) findViewById(R.id.clk);
  dialog = new Dialog(this);
  dialog.setContentView(R.layout.dialog);
  clk.setOnClickListener(new OnClickListener() {

   @Override
   public void onClick(View v) {
    dialog.show();
   }
  });
 }
}

当我们点击按钮时，会弹出对话框（内容为android logo），当我们旋转屏幕后，Activity重新创建，整个Activity的界面没有问题，而对话框消失了。
除此之外，其实还有一个问题，就是在logcat中会看到异常信息：Android..leaked .. window，这是因为在Activity结束之前，Android要求所有的Dialog必须要关闭。我们旋屏后，Activity会被重建，而上面的代码逻辑并没有考虑到对话框的状态以及是否已关闭。

于是将上述代码修改为：

public class MainActivity extends Activity {
 private Button clk;
 private Dialog dialog;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  clk = (Button) findViewById(R.id.clk);
  dialog = new Dialog(this);
  dialog.setContentView(R.layout.dialog);
  clk.setOnClickListener(new OnClickListener() {

   @Override
   public void onClick(View v) {
    dialog.show();
   }
  });

  //用户恢复对话框的状态
  if(savedInstanceState != null && savedInstanceState.getBoolean("dialog_show"))
   clk.performClick();
 }

 /**
  * 用于保存对话框的状态以便恢复
  */
 @Override
 protected void onSaveInstanceState(Bundle outState) {
  super.onSaveInstanceState(outState);
  if(dialog != null && dialog.isShowing())
   outState.putBoolean("dialog_show", true);
  else
   outState.putBoolean("dialog_show", false);
 }

 /**
  * 在Activity销毁之前，确保对话框以关闭
  */
 @Override
 protected void onDestroy() {
  super.onDestroy();
  if(dialog != null && dialog.isShowing())
   dialog.dismiss();
 }
}

2. 基于DialogFragment的对话框

与上面的对话框使用同样的界面布局，此处仅仅展现一个简单对话框，因此只重写了onCreateView方法

public class MyDialogFragment extends DialogFragment {
 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container,
   Bundle savedInstanceState) {
  View v = inflater.inflate(R.layout.dialog, container, false);
  return v;
 }
}

public class MainActivity extends FragmentActivity {
 private Button clk;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  clk = (Button) findViewById(R.id.clk);
  clk.setOnClickListener(new OnClickListener() {

   @Override
   public void onClick(View v) {
    MyDialogFragment mdf = new MyDialogFragment();
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
    mdf.show(ft, "df");
   }
  });
 }
}

这两段代码可以实现第一种方式的同样功能，此处我们并没有去关心对话框的重建，以及Activity销毁前对话框是否已关闭，这一切都是由FragmentManager来管理。
其实DialogFragment还拥有fragment的优点，即可以在一个Activity内部实现回退（因为FragmentManager会管理一个回退栈）