Preface

There are many ways to create dialog boxes in Android .Dialog、AlertDialog、DialogFragment、PopupWindow even to the extent that Activity Set the theme to Dialog You can also create dialog boxes . among ,AlertDialog and DialogFragment It's all based on Dialog Created .AlertDialog It can be regarded as an official Dialog Wrapper class .DialogFragment Is in Fragment There's an embedded Dialog object , Its biggest advantage is that it can ensure that the previous state remains unchanged when the screen direction is switched , And the official also recommends DialogFragment, So it is gradually used in the project . however , There are also many pits , This article is specially written here to talk about , Also as future notes .

One 、 How to style a dialog box

because dialogFragment There's a built-in dialog Entity , Through this dialog Entity , We can use dialog All the ways to configure this form :

	Window window=getDialog().getWindow();
	window.setWindowAnimations(R.style.BottomWindowAnim);// Set form animation style 
	WindowManager.LayoutParams lp = window.getAttributes();
	lp.gravity = Gravity.BOTTOM;// Set window position 
	lp.dimAmount = 0.7f;// Set the transparency of the mask  0~1
	lp.width = (int) (getResources().getDisplayMetrics().widthPixels*0.8);// Set the width of the form ( It can be a specific pixel value , It can also be WRAP_CONTENT And so on. )
	lp.height = ViewGroup.LayoutParams.WRAP_CONTENT;// Set the height of the form 
	getDialog().onWindowAttributesChanged(lp);// Manual trigger , Application configuration 

Two 、 How to set click the mask or return key to prevent the form from disappearing

Use as before dialog Experience in , We should know ,dialog You can set it like this :

	dialog.setCancelable(false); // Set and click the return key to not disappear 
	dialog.setCanceledOnTouchOutside(false);// Set the click mask not to disappear 

However , When you set it like this , You'll find that , Only by clicking on the mask will it take effect . Clicking the back button can still disappear .

For the processing of the return key , We should call dialogFragment Inside setCancelable To achieve :

	dialogFragment.setCancelable(cancelable);

In fact, the reason for this design is also well understood .dialog Inside cancelable It can only control itself , And its host fragment It's out of control . So this method should be written in fragment Inside .

3、 ... and 、 call getDialog() return null

For example, in the above question , Set up canceledOnTouchOutside The time has come getDialog() Null pointer exception . To understand the problem , Let's take a brief look at dialogFragment What key stages will you go through when creating .

	@Override
    public void onAttach(@NonNull Context context) {
    
        super.onAttach(context);
        Log.d(TAG, "onAttach.getDialog->" + getDialog());
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate.getDialog->" + getDialog());
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
    
        Log.d(TAG, "onCreateDialog.getDialog->" + getDialog());
        return super.onCreateDialog(savedInstanceState);
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    
        Log.d(TAG, "onCreateView.getDialog->" + getDialog());
        rootView = inflater.inflate(getLayoutId(), null);
        return rootView;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    
        super.onViewCreated(view, savedInstanceState);
        Log.d(TAG, "onViewCreated.getDialog->" + getDialog());
    }

I put the log tag in the above code , Let's take a look at :

2021-09-18 09:51:56.779 15075-15075/com.cjs.kotlinapp D/BDF: onAttach.getDialog->null
2021-09-18 09:51:56.780 15075-15075/com.cjs.kotlinapp D/BDF: onCreate.getDialog->null
2021-09-18 09:51:56.780 15075-15075/com.cjs.kotlinapp D/BDF: onCreateDialog.getDialog->null
2021-09-18 09:51:56.786 15075-15075/com.cjs.kotlinapp D/BDF: onCreateView.getDialog->android.app.Dialog@8983aa6
2021-09-18 09:51:56.836 15075-15075/com.cjs.kotlinapp D/BDF: onViewCreated.getDialog->android.app.Dialog@8983aa6

It's not hard to see. ,getDialog() from onCreateView Start , It's worth it .
actually ,getDialog The return is onCreateDialog In return dialog.

in other words , The earliest we can get dialog Value stage , Namely onCreateDialog in , But write it in this form :

	@NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
    
        Dialog dialog = super.onCreateDialog(savedInstanceState);
  		// Here you can write some dialog Configuration operation of , for example 
  		dialog.setCanceledOnTouchOutside(false);
        return dialog;
    }

therefore , The earliest we can set canceledOnTouchOutside The stage of , This is it . thus , There will be no null pointer exception .

Four 、 Abnormal display of form size

1、 Problem recurrence

for instance , When customizing the dialog box , The form you see after configuration is like this :

Window layout :

<?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" android:padding="10dp">

    <TextView android:id="@+id/tv_title" android:layout_width="wrap_content" android:layout_height="wrap_content" android:gravity="center_vertical" android:drawableLeft="@drawable/ic__info" android:drawablePadding="2dp" android:textColor="@color/dialog_title" android:textSize="18sp" />

    <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="8dp" android:gravity="center" android:orientation="vertical">

        <TextView android:id="@+id/tv_msg" android:minLines="2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:textColor="@color/dialog_msg" android:textSize="14sp" />
    </LinearLayout>

    <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:gravity="right" android:orientation="horizontal">
        <!-- The buttons here use TextView Rather than using Button The reason is that Button There will be a default background inside , Own width and height , It's not easy to format -->
        <TextView android:visibility="gone" android:id="@+id/btn_cancel" style="@style/DialogButton" android:textColor="@color/dialog_button_cancel" />

        <TextView android:id="@+id/btn_submit" style="@style/DialogButton"/>
    </LinearLayout>
    
</LinearLayout>

It's simple , It's an external one LinearLayout. Then the outer layout is wide and high match_parent.

2、 Problem analysis & solve

The reason for the abnormal display of the above form is that when you use the first point of this article to configure the dialog box , Those codes are filled in the wrong place . Let's look at the first line of code :

Window window=getDialog().getWindow();

First , Need to ensure getDialog() Can't be empty . Based on the previous analysis , As early as onCreateDialog Get value in it . But if you write the code of the first point here , congratulations , Successfully captured an abnormal pop-up window .
Why? ？ Think about our line of code , We don't operate dialog, It's inside window object . We set the width and height of the dialog box to match_parent. Therefore, it will involve the width and height of its host layout . The host of the dialog box is fragment,fragment When creating a layout, it is in onCreateView in .view When the creation is completed, it is in onViewCreated(View v) in , Inside v Namely onCreateView The one returned in .view After you create , Naturally, there is the width and height of the host layout , Then call the method of the first point , Can solve the problem .

	@Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    
        super.onViewCreated(view, savedInstanceState);
        initWindow(getDialog().getWindow());
    }

there initWindow The method is the content of the first point .

5、 ... and 、getActivity() return null

1、 Problem recurrence

dialogFragment There's a way to :

This method is used to display a dialogFragment. These two methods actually correspond to Fragment Some processes during creation . among , first fragmentManager Parameters , In general , We can use activity Of getSupportFragmentManager Come and get it , So , We can encapsulate a simple show Method :

	public void show(){
    
        show(getActivity().getSupportFragmentManager(),"XXXX");
    }

Suppose we customize one MsgDialog Pop-up windows , To display this pop-up window , We can write this way :

MsgDialog d=new MsgDialog();
d.show();

look , It is much simpler than the official method call . But once you run , Will report getActivity() Null pointer exception .

2、 Problem analysis & solve

First , We'll settle it according to the getDialog Think about the empty solution , have a look , Isn't there a step in the life cycle that doesn't get getActivity.

	@Override
    public void onAttach(@NonNull Context context) {
    
        super.onAttach(context);
        Log.d(TAG, "onAttach.getActivity->" + getActivity());
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate.getActivity->" + getActivity());
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
    
        Log.d(TAG, "onCreateDialog.getActivity->" + getActivity());
        return super.onCreateDialog(savedInstanceState);
    }

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    
        Log.d(TAG, "onCreateView.getActivity->" + getActivity());
        rootView = inflater.inflate(getLayoutId(), null);
        return rootView;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    
        super.onViewCreated(view, savedInstanceState);
        Log.d(TAG, "onViewCreated.getActivity->" + getActivity());
    }

But a look at the log , Just stunned :

2021-09-18 10:48:06.645 15631-15631/com.cjs.kotlinapp D/BDF: onAttach.getActivity->com.cjs.kotlinapp.MainActivity@97996d1
2021-09-18 10:48:06.645 15631-15631/com.cjs.kotlinapp D/BDF: onCreate.getActivity->com.cjs.kotlinapp.MainActivity@97996d1
2021-09-18 10:48:06.645 15631-15631/com.cjs.kotlinapp D/BDF: onCreateDialog.getActivity->com.cjs.kotlinapp.MainActivity@97996d1
2021-09-18 10:48:06.648 15631-15631/com.cjs.kotlinapp D/BDF: onCreateView.getActivity->com.cjs.kotlinapp.MainActivity@97996d1
2021-09-18 10:48:06.678 15631-15631/com.cjs.kotlinapp D/BDF: onViewCreated.getActivity->com.cjs.kotlinapp.MainActivity@97996d1

All life cycles can get values .onAttach It's the earliest , You can get values here , Naturally, the back can .
Is there anything better than attach Earlier ？ Think about it. , only MsgDialog The constructor for ., So , I also printed it in the constructor , As a result, the cause of the problem was found :

2021-09-18 10:48:06.628 15631-15631/com.cjs.kotlinapp D/BDF:  structure 
2021-09-18 10:48:06.645 15631-15631/com.cjs.kotlinapp D/BDF: onAttach.getActivity->com.cjs.kotlinapp.MainActivity@97996d1
2021-09-18 10:48:06.645 15631-15631/com.cjs.kotlinapp D/BDF: onCreate.getActivity->com.cjs.kotlinapp.MainActivity@97996d1
2021-09-18 10:48:06.645 15631-15631/com.cjs.kotlinapp D/BDF: onCreateDialog.getActivity->com.cjs.kotlinapp.MainActivity@97996d1
2021-09-18 10:48:06.648 15631-15631/com.cjs.kotlinapp D/BDF: onCreateView.getActivity->com.cjs.kotlinapp.MainActivity@97996d1
2021-09-18 10:48:06.678 15631-15631/com.cjs.kotlinapp D/BDF: onViewCreated.getActivity->com.cjs.kotlinapp.MainActivity@97996d1

We show the operation of the form , First new Again show. only new When , Will find , Not going dialogFragment Any life cycle of , If you leave , Must be calling show after . Then I went to see show Source code :

	/** * Display the dialog, adding the fragment to the given FragmentManager. This * is a convenience for explicitly creating a transaction, adding the * fragment to it with the given tag, and {@link FragmentTransaction#commit() committing} it. * This does <em>not</em> add the transaction to the fragment back stack. When the fragment * is dismissed, a new transaction will be executed to remove it from * the activity. * @param manager The FragmentManager this fragment will be added to. * @param tag The tag for this fragment, as per * {@link FragmentTransaction#add(Fragment, String) FragmentTransaction.add}. */
    public void show(@NonNull FragmentManager manager, @Nullable String tag) {
    
        mDismissed = false;
        mShownByMe = true;
        FragmentTransaction ft = manager.beginTransaction();
        ft.add(this, tag);
        ft.commit();
    }

Found only when calling show Only when I go to FragmentTransaction Add fragment And then commit. So the answer is clear , only new It's only equivalent to creating a hair dryer , Only a call show Plug in the power , The wind will turn .
So let's be honest where to call , Just where fragmentManager.