前言
最近在研究设计模式中的建造者模式，而AlertDialog源码正是采用这种模式进行设计的，故将整个AlertDialog源码都给分析了一遍。
总体框架
在MainActivity中实例化一个AlertDialog对象：
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new AlertDialog.Builder(this)
.setTitle("标题")
.setMessage("内容")
.show();
}
}
源码分析，整个时序图如下：
1.png
源码分析
1.首先我们在MainActivity中实例化一个AlertDialog.Builder对象，构造方法如下：
public Builder(Context context, int themeResId) {
P = new AlertController.AlertParams(new ContextThemeWrapper(
context, resolveDialogTheme(context, themeResId)));
}
在这个构造方法中会实例化AlertController.AlertParams对象，其实这个AlertParams就是我们传递的某些设置，诸如title、message等。
如果没做任何处理，Android Studio乃至其它的IDE是无法查看Android隐藏的源码的，而AlertController属于隐藏的源码，我们该怎么处理呢？可以查看我的另外一个博客：Android Studio 查看Android内部隐藏源码
2.然后我们调用show方法，show方法内部如下：
public AlertDialog show() {
final AlertDialog dialog = create();
dialog.show();
return dialog;
}
调用AlertDialog内部类Builder中的create方法，我们可以看看create方法内部做了哪些处理：
public AlertDialog create() {
// Context has already been wrapped with the appropriate theme.
final AlertDialog dialog = new AlertDialog(P.mContext, 0, false);
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;
}
创建了AlertDialog对象，并调用AlertParams对象的apply方法，接着就是给AlertDialog设置一些监听器。我们来仔细看看这个apply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);
}
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);
}
/*
dialog.setCancelable(mCancelable);
dialog.setOnCancelListener(mOnCancelListener);
if (mOnKeyListener != null) {
dialog.setOnKeyListener(mOnKeyListener);
}
*/
}
其实这里也没什么，无非就是将我们通过链式调用设置的一些重新设置到AlertController中。
3.接下来我们返回到Builder类的show方法：
public AlertDialog show() {
final AlertDialog dialog = create();
dialog.show();
return dialog;
}
我们已经查看了create方法，再来看dialog.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();
}
其实这里是调用父类Dialog的show方法，可以看到调用了dispatchOnCreate方法，点击进去：
void dispatchOnCreate(Bundle savedInstanceState) {
if (!mCreated) {
onCreate(savedInstanceState);
mCreated = true;
}
}
调用了onCreate方法，点击进去，Dialog类没有任何实现，这时候我们想到它的子类AlertDialog，去这个类找onCreate的实现：
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mAlert.installContent();
}
调用了AlertController对象的installContent方法，点击进去：
public void installContent() {
int contentView = selectContentView();
mWindow.setContentView(contentView);
setupView();
}
可以看到这里调用了setupView方法，点击进去：
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);
```
```
}
原来真正的布局与设置都是在这里，如果拿房子举例来说，这个AlertController类才是房子，而AlertDialog这个类是建造者Builder，只不过它将Builder又封装了一层而已。
这里我们看到了熟悉的findViewById，那么有人又会想，那布局到底是哪一个呢？其实是alert_dialog，我们可以在AlertController这个类中搜索alert_dialog即可。
总结
细细查看一些Android源码，其实也没那么难，关键在于事在人为，但是对于一些为何要这样设计，这样设计有什么好处，这个就需要我们花时间去深思其中的奥秘！
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