AlertDialog采用了builder建造者模式，今天咱们来分析下它是怎样与view关联起来并进行绘制的。
先看看大致源码。
public class AlertDialog extends AppCompatDialog implements DialogInterface {
final AlertController mAlert;
protected AlertDialog(@NonNull Context context) {
this(context, 0);
}
protected AlertDialog(@NonNull Context context, @StyleRes int themeResId) {
super(context, resolveDialogTheme(context, themeResId));
mAlert = new AlertController(getContext(), this, getWindow());
}
protected AlertDialog(@NonNull Context context, boolean cancelable,
@Nullable OnCancelListener cancelListener) {
this(context, 0);
setCancelable(cancelable);
setOnCancelListener(cancelListener);
}
@Override
public void setTitle(CharSequence title) {
super.setTitle(title);
mAlert.setTitle(title);
}
public void setView(View view) {
mAlert.setView(view);
}
public void setView(View view, int viewSpacingLeft, int viewSpacingTop, int viewSpacingRight,
int viewSpacingBottom) {
mAlert.setView(view, viewSpacingLeft, viewSpacingTop, viewSpacingRight, viewSpacingBottom);
}
//设置其他属性...
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mAlert.installContent();
}
public static class Builder {
private final AlertController.AlertParams P;
private final int mTheme;
public Builder(@NonNull Context context) {
this(context, resolveDialogTheme(context, 0));
}
public Builder(@NonNull Context context, @StyleRes int themeResId) {
P = new AlertController.AlertParams(new ContextThemeWrapper(
context, resolveDialogTheme(context, themeResId)));
mTheme = themeResId;
}
public Builder setTitle(@StringRes int titleId) {
P.mTitle = P.mContext.getText(titleId);
return this;
}
public Builder setCustomTitle(@Nullable View customTitleView) {
P.mCustomTitleView = customTitleView;
return this;
}
public Builder setView(int layoutResId) {
P.mView = null;
P.mViewLayoutResId = layoutResId;
P.mViewSpacingSpecified = false;
return this;
}
//设置其他属性...
public AlertDialog create() {
// We can't use Dialog's 3-arg constructor with the createThemeContextWrapper param,
// so we always have to re-set the theme
final AlertDialog dialog = new AlertDialog(P.mContext, mTheme);
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 AlertDialog show() {
final AlertDialog dialog = create();
dialog.show();
return dialog;
}
}
}
如上，大致构造就是AlertDialog内部有一个Builder内部类，通过它可以设置dialog的各种属性，Builder内部有一个AlertController.AlertParams变量P，负责把外部设置的属性保存下来，然后在create()方法里面将这些属性传递给AlertDialog的AlertController变量mAlert，具体方法是P.apply(dialog.mAlert)。实际将AlertParams就是AlertController的内部类，为什么P的类型不直接设置成AlertController呢？因为从名字上我们可以看出，AlertParams显然只负责保存和设置参数，而AlertController还有更多，所以用了一个内部类。
看看P.apply(dialog.mAlert)方法。
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);
}
//设置其他属性...
*/
}
可以看出，这个方法就是将title、icon、layout等各种属性传回给AlertController本身。
属性设置后，再调用show()函数就可以创建出对话框了。因此我们再看show()方法。
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) {
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();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION) == 0) {
WindowManager.LayoutParams nl = new WindowManager.LayoutParams();
nl.copyFrom(l);
nl.softInputMode |=
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
l = nl;
}
mWindowManager.addView(mDecor, l);
mShowing = true;
sendShowMessage();
}
show()函数主要做了这几个事情：
1、先判断当前的显示状态，如果是已经show了，则返回。如果不是，那么通过dispatchOnCreate()调用onCreate函数，然后调用onStart函数。
2、将decorView添加到windowManager里面，并发送一个显示dialog的消息。
很显然，这就是一系列生命周期的函数（onCreate()、onStart()），因此视图的创建应该在onCreate()函数里。看下是不是：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mAlert.installContent();
}
父类dialog的onCreate方法是一个空实现，因此看AlertDialog的onCreate方法，而具体还看mAlert.installContent()：
public void installContent() {
final int contentView = selectContentView();
mDialog.setContentView(contentView);
setupView();
}
setContentView是不是很熟悉，这个和activity的setContentView几乎一模一样，继续追踪我们发现，最终都是调用了window对象的setContentView方法。
继续看setupView():
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);
}
}
}
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) {
divider = topPanel.findViewById(R.id.titleDividerNoCustom);
}
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 ? ViewCompat.SCROLL_INDICATOR_TOP : 0)
| (hasButtonPanel ? ViewCompat.SCROLL_INDICATOR_BOTTOM : 0);
setScrollIndicators(contentPanel, content, indicators,
ViewCompat.SCROLL_INDICATOR_TOP | ViewCompat.SCROLL_INDICATOR_BOTTOM);
}
}
final ListView listView = mListView;
if (listView != null && mAdapter != null) {
listView.setAdapter(mAdapter);
final int checkedItem = mCheckedItem;
if (checkedItem > -1) {
listView.setItemChecked(checkedItem, true);
listView.setSelection(checkedItem);
}
}
}
此方法就是设置了alertDialog的各个区域布局，如标题、按钮、标题icon以及内容等等。当用户调用show函数时，windowManager会将window对象的DecorView添加到用户的窗口上，并显示出来，至此，整个dialog就出现在屏幕上了。