Android UI篇——DialogFragment系列一之源码分析

《DialogFragment系列一之源码分析》
《DialogFragment系列二之Dialog封装》
《DialogFragment系列三之AlertDialog实现》
《DialogFragment系列四之StatusDialog(Progress、Success、Error)实现》
《DialogFragment系列五之ItemDialog(eg:BottomDialog)实现》
《DialogFragment系列六之常见问题》

Android日常开发中，每一个APP都有使用弹框来进行交互的需求，最常用的有Dialog、PopUpWindow、Toast、SnackBar，有交互的操作最常用的还是Dialog，Android API已经为开发者提供了AlertDialog，相比不少读者都在使用它，但是AlertDialog有一个很大的缺点就是不受Activity/Fragment生命周期的管理，很容易出现Crash，而且屏幕切换以后还不能自动保留状态等，所以Android提供了另一个DialogFragment专门来解决这些问题，而且Google和阿里Android开发手册中都推荐使用DialogFrgament，不推荐使用AlertDialog或其他自定义AlertDialog。

下面就从DialogFragment的优点和使用来展开，想来想去还是直接从源码分析比较直观和有说服力。

源码如下：

public class DialogFragment extends Fragment
        implements DialogInterface.OnCancelListener, DialogInterface.OnDismissListener {

    /** @hide */
    @RestrictTo(LIBRARY_GROUP)
    @IntDef({STYLE_NORMAL, STYLE_NO_TITLE, STYLE_NO_FRAME, STYLE_NO_INPUT})
    @Retention(RetentionPolicy.SOURCE)
    private @interface DialogStyle {}

    public static final int STYLE_NORMAL = 0;

    public static final int STYLE_NO_TITLE = 1;

    public static final int STYLE_NO_FRAME = 2;

    public static final int STYLE_NO_INPUT = 3;

    private static final String SAVED_DIALOG_STATE_TAG = "android:savedDialogState";
    private static final String SAVED_STYLE = "android:style";
    private static final String SAVED_THEME = "android:theme";
    private static final String SAVED_CANCELABLE = "android:cancelable";
    private static final String SAVED_SHOWS_DIALOG = "android:showsDialog";
    private static final String SAVED_BACK_STACK_ID = "android:backStackId";

    int mStyle = STYLE_NORMAL;
    int mTheme = 0;
    boolean mCancelable = true;
    boolean mShowsDialog = true;
    int mBackStackId = -1;

    Dialog mDialog;
    boolean mViewDestroyed;
    boolean mDismissed;
    boolean mShownByMe;

    public DialogFragment() {
    }

    public void setStyle(@DialogStyle int style, @StyleRes int theme) {
        mStyle = style;
        if (mStyle == STYLE_NO_FRAME || mStyle == STYLE_NO_INPUT) {
            mTheme = android.R.style.Theme_Panel;
        }
        if (theme != 0) {
            mTheme = theme;
        }
    }

     public void show(FragmentManager manager, String tag) {
        mDismissed = false;
        mShownByMe = true;
        FragmentTransaction ft = manager.beginTransaction();
        ft.add(this, tag);
        ft.commit();
    }

    public int show(FragmentTransaction transaction, String tag) {
        mDismissed = false;
        mShownByMe = true;
        transaction.add(this, tag);
        mViewDestroyed = false;
        mBackStackId = transaction.commit();
        return mBackStackId;
    }

    public void showNow(FragmentManager manager, String tag) {
        mDismissed = false;
        mShownByMe = true;
        FragmentTransaction ft = manager.beginTransaction();
        ft.add(this, tag);
        ft.commitNow();
    }

    public void dismiss() {
        dismissInternal(false);
    }
    public void dismissAllowingStateLoss() {
        dismissInternal(true);
    }

    void dismissInternal(boolean allowStateLoss) {
        if (mDismissed) {
            return;
        }
        mDismissed = true;
        mShownByMe = false;
        if (mDialog != null) {
            mDialog.dismiss();
        }
        mViewDestroyed = true;
        if (mBackStackId >= 0) {
            getFragmentManager().popBackStack(mBackStackId,
                    FragmentManager.POP_BACK_STACK_INCLUSIVE);
            mBackStackId = -1;
        } else {
            FragmentTransaction ft = getFragmentManager().beginTransaction();
            ft.remove(this);
            if (allowStateLoss) {
                ft.commitAllowingStateLoss();
            } else {
                ft.commit();
            }
        }
    }

    public Dialog getDialog() {
        return mDialog;
    }

    @StyleRes
    public int getTheme() {
        return mTheme;
    }
    public void setCancelable(boolean cancelable) {
        mCancelable = cancelable;
        if (mDialog != null) mDialog.setCancelable(cancelable);
    }

    /**
     * Return the current value of {@link #setCancelable(boolean)}.
     */
    public boolean isCancelable() {
        return mCancelable;
    }

    public void setShowsDialog(boolean showsDialog) {
        mShowsDialog = showsDialog;
    }

    /**
     * Return the current value of {@link #setShowsDialog(boolean)}.
     */
    public boolean getShowsDialog() {
        return mShowsDialog;
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (!mShownByMe) {
            // If not explicitly shown through our API, take this as an
            // indication that the dialog is no longer dismissed.
            mDismissed = false;
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        if (!mShownByMe && !mDismissed) {
            // The fragment was not shown by a direct call here, it is not
            // dismissed, and now it is being detached...  well, okay, thou
            // art now dismissed.  Have fun.
            mDismissed = true;
        }
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mShowsDialog = mContainerId == 0;

        if (savedInstanceState != null) {
            mStyle = savedInstanceState.getInt(SAVED_STYLE, STYLE_NORMAL);
            mTheme = savedInstanceState.getInt(SAVED_THEME, 0);
            mCancelable = savedInstanceState.getBoolean(SAVED_CANCELABLE, true);
            mShowsDialog = savedInstanceState.getBoolean(SAVED_SHOWS_DIALOG, mShowsDialog);
            mBackStackId = savedInstanceState.getInt(SAVED_BACK_STACK_ID, -1);
        }
    }

    @Override
    @NonNull
    public LayoutInflater onGetLayoutInflater(@Nullable Bundle savedInstanceState) {
        if (!mShowsDialog) {
            return super.onGetLayoutInflater(savedInstanceState);
        }

        mDialog = onCreateDialog(savedInstanceState);

        if (mDialog != null) {
            setupDialog(mDialog, mStyle);

            return (LayoutInflater) mDialog.getContext().getSystemService(
                    Context.LAYOUT_INFLATER_SERVICE);
        }
        return (LayoutInflater) mHost.getContext().getSystemService(
                Context.LAYOUT_INFLATER_SERVICE);
    }

    /** @hide */
    @RestrictTo(LIBRARY_GROUP)
    public void setupDialog(Dialog dialog, int style) {
        switch (style) {
            case STYLE_NO_INPUT:
                dialog.getWindow().addFlags(
                        WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
                                WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE);
                // fall through...
            case STYLE_NO_FRAME:
            case STYLE_NO_TITLE:
                dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        }
    }

    @NonNull
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        return new Dialog(getActivity(), getTheme());
    }

    @Override
    public void onCancel(DialogInterface dialog) {
    }

    @Override
    public void onDismiss(DialogInterface dialog) {
        if (!mViewDestroyed) {
            // Note: we need to use allowStateLoss, because the dialog
            // dispatches this asynchronously so we can receive the call
            // after the activity is paused.  Worst case, when the user comes
            // back to the activity they see the dialog again.
            dismissInternal(true);
        }
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        if (!mShowsDialog) {
            return;
        }

        View view = getView();
        if (view != null) {
            if (view.getParent() != null) {
                throw new IllegalStateException(
                        "DialogFragment can not be attached to a container view");
            }
            mDialog.setContentView(view);
        }
        final Activity activity = getActivity();
        if (activity != null) {
            mDialog.setOwnerActivity(activity);
        }
        mDialog.setCancelable(mCancelable);
        mDialog.setOnCancelListener(this);
        mDialog.setOnDismissListener(this);
        if (savedInstanceState != null) {
            Bundle dialogState = savedInstanceState.getBundle(SAVED_DIALOG_STATE_TAG);
            if (dialogState != null) {
                mDialog.onRestoreInstanceState(dialogState);
            }
        }
    }

    @Override
    public void onStart() {
        super.onStart();

        if (mDialog != null) {
            mViewDestroyed = false;
            mDialog.show();
        }
    }

    @Override
    public void onSaveInstanceState(@NonNull Bundle outState) {
        super.onSaveInstanceState(outState);
        if (mDialog != null) {
            Bundle dialogState = mDialog.onSaveInstanceState();
            if (dialogState != null) {
                outState.putBundle(SAVED_DIALOG_STATE_TAG, dialogState);
            }
        }
        if (mStyle != STYLE_NORMAL) {
            outState.putInt(SAVED_STYLE, mStyle);
        }
        if (mTheme != 0) {
            outState.putInt(SAVED_THEME, mTheme);
        }
        if (!mCancelable) {
            outState.putBoolean(SAVED_CANCELABLE, mCancelable);
        }
        if (!mShowsDialog) {
            outState.putBoolean(SAVED_SHOWS_DIALOG, mShowsDialog);
        }
        if (mBackStackId != -1) {
            outState.putInt(SAVED_BACK_STACK_ID, mBackStackId);
        }
    }

    @Override
    public void onStop() {
        super.onStop();
        if (mDialog != null) {
            mDialog.hide();
        }
    }

    /**
     * Remove dialog.
     */
    @Override
    public void onDestroyView() {
        super.onDestroyView();
        if (mDialog != null) {
            mViewDestroyed = true;
            mDialog.dismiss();
            mDialog = null;
        }
    }
}

DialogFragment是个什么东东？

我们看到DialogFragment直接继承自Fragment，但是实现了DialogInterface.OnCancelListener, DialogInterface.OnDismissListener，这俩接口熟悉不？再看里面onCreateDialog这个方法，我们可以发现DialogFragment就是Dialog和Fragment的合体。

为什么DialogFragment可以解决Dialog不能保存状态的问题？

状态数据保存：

    @Override
    public void onSaveInstanceState(@NonNull Bundle outState) {
        super.onSaveInstanceState(outState);
        if (mDialog != null) {
            Bundle dialogState = mDialog.onSaveInstanceState();
            if (dialogState != null) {
                outState.putBundle(SAVED_DIALOG_STATE_TAG, dialogState);
            }
        }
        if (mStyle != STYLE_NORMAL) {
            outState.putInt(SAVED_STYLE, mStyle);
        }
        if (mTheme != 0) {
            outState.putInt(SAVED_THEME, mTheme);
        }
        if (!mCancelable) {
            outState.putBoolean(SAVED_CANCELABLE, mCancelable);
        }
        if (!mShowsDialog) {
            outState.putBoolean(SAVED_SHOWS_DIALOG, mShowsDialog);
        }
        if (mBackStackId != -1) {
            outState.putInt(SAVED_BACK_STACK_ID, mBackStackId);
        }
    }

状态保存数据取出:

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mShowsDialog = mContainerId == 0;

        if (savedInstanceState != null) {
            mStyle = savedInstanceState.getInt(SAVED_STYLE, STYLE_NORMAL);
            mTheme = savedInstanceState.getInt(SAVED_THEME, 0);
            mCancelable = savedInstanceState.getBoolean(SAVED_CANCELABLE, true);
            mShowsDialog = savedInstanceState.getBoolean(SAVED_SHOWS_DIALOG, mShowsDialog);
            mBackStackId = savedInstanceState.getInt(SAVED_BACK_STACK_ID, -1);
        }
    }

状态数据取出后直接复制给成员变量，这样全局只要使用到就可设置相关属性，这样就达到了状态保存的目的，其实就是使用了Fragment状态保存机制(savedInstanceState)

为什么DialogFragment的生命周期可控呢？

     @Override
    public void onStart() {
        super.onStart();

        if (mDialog != null) {
            mViewDestroyed = false;
            mDialog.show();
        }
    }
    @Override
    public void onStop() {
        super.onStop();
        if (mDialog != null) {
            mDialog.hide();
        }
    }
    /**
     * Remove dialog.
     */
    @Override
    public void onDestroyView() {
        super.onDestroyView();
        if (mDialog != null) {
            // Set removed here because this dismissal is just to hide
            // the dialog -- we don't want this to cause the fragment to
            // actually be removed.
            mViewDestroyed = true;
            mDialog.dismiss();
            mDialog = null;
        }
    }

    public int show(FragmentTransaction transaction, String tag) {
        mDismissed = false;
        mShownByMe = true;
        transaction.add(this, tag);
        mViewDestroyed = false;
        mBackStackId = transaction.commit();
        return mBackStackId;
    }

从源码中可以看出，Dialog的显示、隐藏和销毁分别在Fragment的onStart()、onStop()、onDestroyView()中做了处理，而我们看DialogFragment的show方法需要传入FragmentTransaction参数，也就是说DialogFragment完全受FragmentManager的管理即生命周期就普通Fragment无异，所以Dialog就被Fragment给“控制”了，就再也不会出现放浪不羁的情形了！

DialogFragment怎样使用？

 public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        return new Dialog(getActivity(), getTheme());
 }

从源码中发现了这样一个方法，就是这个方法提供Dialog，所以我们可以通过重写这个方法来自定义DialogFragment，例如可以直接将AlertDialog写进去，其实这是体现了DialogFragment的Dialog属性，那么既然是Fragment，那就可以通过Fragment一个布局实现自定义（因为不重写onCreateDialog的话有默认）即重写onCreateView()来实现，这就是自定义DialogFragment主要的两个方法。

好了，针对DialogFragment的分析和使用就到这里吧，如果你还是使用普通的Dialog的话赶紧换成DialogFragment吧，省心省力省事！！！