我们知道AlertDialog是使用建造者模式构建的，方便将复杂的构建过程进行封装隔离，并将其初始化过程延迟到使用的时候才创建。使用链式编程，方便调用者使用。
AlertDialog.Builder(this).setTitle("标题").create().show()一行代码即可创建一个弹窗。
我们先看一看AlertDialog的类结构图，对其有个大致了解及其主要方法和属性。
AlertDialog类图.png
AlertDialog继承自Dialog，其含有静态内部类Builder，持有AlertController的引用mAlert。AlertController含有静态内部类AlertParams，Builder内部持有AlertParams的引用P。
现在对其结构有了大致了解后，我们看看其方法调用时序图，在我们脑海中有个印象，便于下面源码分析。
AlertDialog时序图.png
我们通过
AlertDialog.Builder(this)创建Builder对象，然后通过各种setXX(XXX)设置状态，其实这里并没有直接将我们设置的状态直接保存到AlertDialog中，而是将其保存到AlertParams中。
public static class Builder {
//用于保存对AlertDialog的状态设置
private final AlertController.AlertParams P;
...
public Builder(Context context, int themeResId) {
//创建AlertParams
P = new AlertController.AlertParams(new ContextThemeWrapper(
context, resolveDialogTheme(context, themeResId)));
}
public Builder setTitle(@StringRes int titleId) {
//属性设置并保存到AlertParams 中
P.mTitle = P.mContext.getText(titleId);
return this;
}
...
public AlertDialog create() {
// 创建AlertDialog 对象，并初始化AlertController
final AlertDialog dialog = new AlertDialog(P.mContext, 0, false);
//调用AlertParams的apply
P.apply(dialog.mAlert);
dialog.setCancelable(P.mCancelable);
if (P.mCancelable) {
dialog.setCanceledOnTouchOutside(true);
}
dialog.setOnCancelListener(P.mOnCancelListener);
dialog.setOnDismissListener(P.mOnDismissListener);
if (P.mOnKeyListener != null) {
dialog.setOnKeyListener(P.mOnKeyListener);
}
return dialog;
}
...
}
public class AlertDialog extends Dialog implements DialogInterface {
//用于转存通过Builder设置的属性（即保存到AlertParams中的属性）
private AlertController mAlert;
...
AlertDialog(Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
super(context, createContextThemeWrapper ? resolveDialogTheme(context, themeResId) : 0,
createContextThemeWrapper);
mWindow.alwaysReadCloseOnTouchAttr();
//创建AlertController
mAlert = AlertController.create(getContext(), this, getWindow());
}
...
//通过调用Dialog的show()，然后调用Dialog的dispatchOnCreate()，最终回调onCreate()初始化AlertDialog的属性
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//将AlertController 转存的属性设置到AlerDialog中
mAlert.installContent();
}
...
//将Builder中设置的状态，转存到AlertController中，由AlertParams 的apply()回调
@Override
public void setTitle(CharSequence title) {
super.setTitle(title);
mAlert.setTitle(title);
}
...
}
public static class AlertParams {
public final Context mContext;
public final LayoutInflater mInflater;
public int mIconId = 0;
public Drawable mIcon;
public int mIconAttrId = 0;
public CharSequence mTitle;
public View mCustomTitleView;
public CharSequence mMessage;
public CharSequence mPositiveButtonText;
...
//将Builder中设置给AlertParams 的属性状态通过调用AlertDialog的setXX(XX)方法转存到AlertController 中
public void apply(AlertController dialog) {
if (mCustomTitleView != null) {
dialog.setCustomTitle(mCustomTitleView);
} else {
if (mTitle != null) {
dialog.setTitle(mTitle);
}
if (mIcon != null) {
dialog.setIcon(mIcon);
}
if (mIconId != 0) {
dialog.setIcon(mIconId);
}
if (mIconAttrId != 0) {
dialog.setIcon(dialog.getIconAttributeResId(mIconAttrId));
}
}
if (mMessage != null) {
dialog.setMessage(mMessage);
}
if (mPositiveButtonText != null) {
dialog.setButton(DialogInterface.BUTTON_POSITIVE, mPositiveButtonText,
mPositiveButtonListener, null);
}
if (mNegativeButtonText != null) {
dialog.setButton(DialogInterface.BUTTON_NEGATIVE, mNegativeButtonText,
mNegativeButtonListener, null);
}
if (mNeutralButtonText != null) {
dialog.setButton(DialogInterface.BUTTON_NEUTRAL, mNeutralButtonText,
mNeutralButtonListener, null);
}
if (mForceInverseBackground) {
dialog.setInverseBackgroundForced(true);
}
// For a list, the client can either supply an array of items or an
// adapter or a cursor
if ((mItems != null) || (mCursor != null) || (mAdapter != null)) {
createListView(dialog);
}
if (mView != null) {
if (mViewSpacingSpecified) {
dialog.setView(mView, mViewSpacingLeft, mViewSpacingTop, mViewSpacingRight,
mViewSpacingBottom);
} else {
dialog.setView(mView);
}
} else if (mViewLayoutResId != 0) {
dialog.setView(mViewLayoutResId);
}
}
...
}
public class AlertController {
private CharSequence mTitle;
private CharSequence mButtonNegativeText;
private Message mButtonNegativeMessage;
...
//转存AlertParams 中的保存的属性状态
public void setTitle(CharSequence title) {
mTitle = title;
if (mTitleView != null) {
mTitleView.setText(title);
}
}
...
public void installContent() {
int contentView = selectContentView();
mWindow.setContentView(contentView);
setupView();
}
//将转存的属性状态设置给AlertDialog
private void setupView() {
final View parentPanel = mWindow.findViewById(R.id.parentPanel);
final View defaultTopPanel = parentPanel.findViewById(R.id.topPanel);
final View defaultContentPanel = parentPanel.findViewById(R.id.contentPanel);
final View defaultButtonPanel = parentPanel.findViewById(R.id.buttonPanel);
// Install custom content before setting up the title or buttons so
// that we can handle panel overrides.
final ViewGroup customPanel = (ViewGroup) parentPanel.findViewById(R.id.customPanel);
setupCustomContent(customPanel);
final View customTopPanel = customPanel.findViewById(R.id.topPanel);
final View customContentPanel = customPanel.findViewById(R.id.contentPanel);
final View customButtonPanel = customPanel.findViewById(R.id.buttonPanel);
// Resolve the correct panels and remove the defaults, if needed.
final ViewGroup topPanel = resolvePanel(customTopPanel, defaultTopPanel);
final ViewGroup contentPanel = resolvePanel(customContentPanel, defaultContentPanel);
final ViewGroup buttonPanel = resolvePanel(customButtonPanel, defaultButtonPanel);
setupContent(contentPanel);
setupButtons(buttonPanel);
setupTitle(topPanel);
final boolean hasCustomPanel = customPanel != null
&& customPanel.getVisibility() != View.GONE;
final boolean hasTopPanel = topPanel != null
&& topPanel.getVisibility() != View.GONE;
final boolean hasButtonPanel = buttonPanel != null
&& buttonPanel.getVisibility() != View.GONE;
// Only display the text spacer if we don't have buttons.
if (!hasButtonPanel) {
if (contentPanel != null) {
final View spacer = contentPanel.findViewById(R.id.textSpacerNoButtons);
if (spacer != null) {
spacer.setVisibility(View.VISIBLE);
}
}
mWindow.setCloseOnTouchOutsideIfNotSet(true);
}
if (hasTopPanel) {
// Only clip scrolling content to padding if we have a title.
if (mScrollView != null) {
mScrollView.setClipToPadding(true);
}
// Only show the divider if we have a title.
View divider = null;
if (mMessage != null || mListView != null || hasCustomPanel) {
if (!hasCustomPanel) {
divider = topPanel.findViewById(R.id.titleDividerNoCustom);
}
if (divider == null) {
divider = topPanel.findViewById(R.id.titleDivider);
}
} else {
divider = topPanel.findViewById(R.id.titleDividerTop);
}
if (divider != null) {
divider.setVisibility(View.VISIBLE);
}
} else {
if (contentPanel != null) {
final View spacer = contentPanel.findViewById(R.id.textSpacerNoTitle);
if (spacer != null) {
spacer.setVisibility(View.VISIBLE);
}
}
}
if (mListView instanceof RecycleListView) {
((RecycleListView) mListView).setHasDecor(hasTopPanel, hasButtonPanel);
}
// Update scroll indicators as needed.
if (!hasCustomPanel) {
final View content = mListView != null ? mListView : mScrollView;
if (content != null) {
final int indicators = (hasTopPanel ? View.SCROLL_INDICATOR_TOP : 0)
| (hasButtonPanel ? View.SCROLL_INDICATOR_BOTTOM : 0);
content.setScrollIndicators(indicators,
View.SCROLL_INDICATOR_TOP | View.SCROLL_INDICATOR_BOTTOM);
}
}
final TypedArray a = mContext.obtainStyledAttributes(
null, R.styleable.AlertDialog, R.attr.alertDialogStyle, 0);
setBackground(a, topPanel, contentPanel, customPanel, buttonPanel,
hasTopPanel, hasCustomPanel, hasButtonPanel);
a.recycle();
}
...
}
然后我们调用AlertDialog的show()即调用父类Dialog的show()方法：
public class Dialog implements DialogInterface, Window.Callback,
KeyEvent.Callback, OnCreateContextMenuListener, Window.OnWindowDismissedCallback {
...
//控制AlertDialog的初始化及生命周期
public void show() {
if (mShowing) {
if (mDecor != null) {
if (mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {
mWindow.invalidatePanelMenu(Window.FEATURE_ACTION_BAR);
}
mDecor.setVisibility(View.VISIBLE);
}
return;
}
mCanceled = false;
if (!mCreated) {
//调用Dialog的onCreate()
dispatchOnCreate(null);
} else {
// Fill the DecorView in on any configuration changes that
// may have occured while it was removed from the WindowManager.
final Configuration config = mContext.getResources().getConfiguration();
mWindow.getDecorView().dispatchConfigurationChanged(config);
}
onStart();
mDecor = mWindow.getDecorView();
if (mActionBar == null && mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {
final ApplicationInfo info = mContext.getApplicationInfo();
mWindow.setDefaultIcon(info.icon);
mWindow.setDefaultLogo(info.logo);
mActionBar = new WindowDecorActionBar(this);
}
WindowManager.LayoutParams l = mWindow.getAttributes();
boolean restoreSoftInputMode = false;
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION) == 0) {
l.softInputMode |=
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
restoreSoftInputMode = true;
}
mWindowManager.addView(mDecor, l);
if (restoreSoftInputMode) {
l.softInputMode &=
~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
}
mShowing = true;
sendShowMessage();
}
void dispatchOnCreate(Bundle savedInstanceState) {
if (!mCreated) {
//调用AlertDialog的onCreate()，然后调用AlertController的installContent()最终完成AlertDialog的初始化
onCreate(savedInstanceState);
mCreated = true;
}
}
...
}
最终AlertDialog的初始化完成。好了，AlertDialog的源码分析到此结束了，我们可以从中学习到，通过建造者模式，将属性封装到AlertParams 中然后转存到AlertController 中，达到复杂参数初始化的隔离，在调用show()方法后，才真正初始化AlertDialog，隔离了外部调用者对其构造过程的了解及控制。