AlertDialog 源码解析一

概要：

AlertDialog，平常用的很多，今天走了一遍内部实现，记录一下。

解析：

一AlertDialog的常用调用：

new AlertDialog.Builder(mContext)
.setTitle("title")
.setMessage("message")
.create()
.show();

这是一个典型的Builder的构建者模式，Builder作为AlertDialog的内部类，专门用于构建AlertDialog对象。

Builder的链式调用，能够很好的简化代码。

AlertDialog与Builder的内部实现：

public class AlertDialog extends Dialog implements DialogInterface {
private AlertController mAlert;

AlertDialog(Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
super(context, createContextThemeWrapper ? resolveDialogTheme(context, themeResId) : 0,
createContextThemeWrapper);

mWindow.alwaysReadCloseOnTouchAttr();
mAlert = AlertController.create(getContext(), this, getWindow());
}

@Override
public void setTitle(CharSequence title) {
super.setTitle(title);
mAlert.setTitle(title);
}

public void setMessage(CharSequence message) {
mAlert.setMessage(message);
}

public static class Builder {
private final AlertController.AlertParams P;

public Builder(Context context, int themeResId) {
P = new AlertController.AlertParams(new ContextThemeWrapper(
context, resolveDialogTheme(context, themeResId)));
}

public Builder setTitle(CharSequence title) {
P.mTitle = title;
return this;
}

public Builder setMessage(@StringRes int messageId) {
P.mMessage = P.mContext.getText(messageId);
return this;
}

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;
}

public AlertDialog show() {
final AlertDialog dialog = create();
dialog.show();
return dialog;
}
}

}

通过上面的代码分析：

1，创建AlertDialog.Builder的时候，会创建AlertController.AlertParams对象P，P里面封装了所有的Dialog

的属性。

2，我们在调用Builder的setTitle，setMessage的时候，其实就是在将方法的参数值赋值给AlertParams P;

3，在Builder的create方法里面，会构建AlertDialog对像dialog。其中P.apply(dialog.mAlert);就是将P的属性

全部设置到Dialog的属性变量mAlert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);
}
//省略了次要代码
}

4，Builder的create方法，最后返回了AlertDialog对象dialog。所以最后show方法，是dialog.show();

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();
}

5，这里会调用dispatchOnCreate(null)，最终会回调AlertDialog的onCreate方法。

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mAlert.installContent();
}
//一下是AlertController类中方法。
public void installContent() {
int contentView = selectContentView();
mWindow.setContentView(contentView);
setupView();
}

private int selectContentView() {
if (mButtonPanelSideLayout == 0) {
return mAlertDialogLayout;
}
if (mButtonPanelLayoutHint == AlertDialog.LAYOUT_HINT_SIDE) {
return mButtonPanelSideLayout;
}
// TODO: use layout hint side for long messages/lists
return mAlertDialogLayout;
}

6，mAlert.installContent，即是在初始化AlertDialog的控件。（即通过fingViewById,关联控件）

7，最后通过mWindowManager.addView(mDecorView, l);加载到屏幕上。

注：

1，由上分析可知，我们如果想要自定义Dialog，继承AlertDialog，重新onCreate方法（给个建议）。

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
initViews(getContext());
}

private void initViews(Context context){
setContentView(R.layout.dialog_horizontal);
tv_title = getWindow().findViewById(R.id.tv_title);
tv_size = getWindow().findViewById(R.id.tv_size);
progressBar = getWindow().findViewById(R.id.progress);

WindowManager.LayoutParams lp = getWindow().getAttributes();
lp.width = DensityUtil.dp2px(context.getApplicationContext(), 320);
//        lp.width = WindowManager.LayoutParams.MATCH_PARENT;
lp.height = WindowManager.LayoutParams.WRAP_CONTENT;
getWindow().setAttributes(lp);
}

2，其中mWindow是PhoneWindow。在AlertDialog的构造方法中生成。

Dialog(@NonNull Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
if (createContextThemeWrapper) {
if (themeResId == ResourceId.ID_NULL) {
final TypedValue outValue = new TypedValue();
context.getTheme().resolveAttribute(R.attr.dialogTheme, outValue, true);
themeResId = outValue.resourceId;
}
mContext = new ContextThemeWrapper(context, themeResId);
} else {
mContext = context;
}

mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

final Window w = new PhoneWindow(mContext);//
mWindow = w;
w.setCallback(this);
w.setOnWindowDismissedCallback(this);
w.setOnWindowSwipeDismissedCallback(() -> {
if (mCancelable) {
cancel();
}
});
w.setWindowManager(mWindowManager, null, null);
w.setGravity(Gravity.CENTER);

mListenersHandler = new ListenersHandler(this);
}