Android SDK范例源码学习系列三 ActionBarCompat

   (本系列基于Jelly Bean,Android OS4.2,API 17版本) 

操作栏Action Bar是在Android3.0版本中引入的，用来替代之前的标题栏。ActionBar提供了更丰富的导航效果，它可用来显示用户动作和全局的菜单选项，还可以增强标识，或者在Fragment之间切换，提供下拉导航栏、显示搜索和分享等动作。.  使用ActionBar很简单，在3.0以后的版本中都默认包含ActionBar组件。如果不想使用，需要将Activity的主题设置为Theme.Holo.NoActionBar：  <activity android:theme="@android:style/Theme.Holo.NoActionBar">  如果仅仅不想显示，可以调用ActionBar.hide()方法，这样当你想显示时，就可以用show()方法达到目的。  本范例中实现了不同版本中ActionBar的兼容功能，一共使用了8个类，下面一一介绍：  ActionBarHelper.class处理ActionBar基础功能的抽象类。实现这个类的是下面的两个类：  ActionBarHelperBase.class 在3.0以前版本中使用，弄明白这个类也就学会了自定义菜单栏的方法  ActionBarHelperHoneycomb在3.0以后版本中使用，后面的类继承了这个类  ActionBarHelperICS在4.0版本后使用，继承了上面类的大部分方法  SimpleMenu.class和SimpleMenuItem是 用于兼容的类，在低版本上使用。  然后就负责具体交互的Activity类MainActivity，继承自实现了ActionBar功能的ActionBarActivity。  下面着重分析ActionBarHelperBase类

package com.example.android.actionbarcompat;import org.import org.import android.app.Activity;import android.content.Context;import android.content.res.import android.os.Bundle;import android.view.InflateException;import android.view.Menu;import android.view.MenuInflater;import android.view.MenuItem;import android.view.View;import android.view.ViewGroup;import android.view.Window;import android.widget.ImageButton;import android.widget.ImageView;import android.widget.LinearLayout;import android.widget.ProgressBar;import android.widget.TextView;import java.io.IOException;import java.util.HashSet;import java.util.Set;/** * A class that implements the action bar pattern for pre-Honeycomb devices. */public class ActionBarHelperBase extends ActionBarHelper {  private static final String MENU_RES_NAMESPACE = "http://schemas.android.com/apk/res/android";  private static final String MENU_ATTR_ID = "id";  private static final String MENU_ATTR_SHOW_AS_ACTION = "showAsAction";  protected Set<Integer> mActionItemIds = new HashSet<Integer>();  protected ActionBarHelperBase(Activity activity) {    super(activity);  }@Overridepublic void onCreate(Bundle savedInstanceState) {    mActivity.requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);  }@Overridepublic void onPostCreate(Bundle savedInstanceState) {    mActivity.getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE,        R.layout.actionbar_compat);    setupActionBar();    SimpleMenu menu = new SimpleMenu(mActivity);    mActivity.onCreatePanelMenu(Window.FEATURE_OPTIONS_PANEL, menu);    mActivity.onPrepareOptionsMenu(menu);    for (int i = 0; i < menu.size(); i++) {      MenuItem item = menu.getItem(i);      if (mActionItemIds.contains(item.getItemId())) {        addActionItemCompatFromMenuItem(item);      }    }  }  /**   * Sets up the compatibility action bar with the given title.   */private void setupActionBar() {    final ViewGroup actionBarCompat = getActionBarCompat();    if (actionBarCompat == null) {      return;    }    LinearLayout.LayoutParams springLayoutParams = new LinearLayout.LayoutParams(        0, ViewGroup.LayoutParams.FILL_PARENT);    springLayoutParams.weight = 1;    // Add Home buttonSimpleMenu tempMenu = new SimpleMenu(mActivity);    SimpleMenuItem homeItem = new SimpleMenuItem(        tempMenu, android.R.id.home, 0, mActivity.getString(R.string.app_name));    homeItem.setIcon(R.drawable.ic_home);    addActionItemCompatFromMenuItem(homeItem);    // Add title textTextView titleText = new TextView(mActivity, null, R.attr.actionbarCompatTitleStyle);    titleText.setLayoutParams(springLayoutParams);    titleText.setText(mActivity.getTitle());    actionBarCompat.addView(titleText);  }@Overridepublic void setRefreshActionItemState(boolean refreshing) {    View refreshButton = mActivity.findViewById(R.id.actionbar_compat_item_refresh);    View refreshIndicator = mActivity.findViewById(        R.id.actionbar_compat_item_refresh_progress);    if (refreshButton != null) {      refreshButton.setVisibility(refreshing ? View.GONE : View.VISIBLE);    }    if (refreshIndicator != null) {      refreshIndicator.setVisibility(refreshing ? View.VISIBLE : View.GONE);    }  }  /**   * NOTE: This code will mark on-screen menu items as invisible.   */@Overridepublic boolean onCreateOptionsMenu(Menu menu) {    // Hides on-screen action items from the options menu.for (Integer id : mActionItemIds) {      menu.findItem(id).setVisible(false);    }    return true;  }@Overrideprotected void onTitleChanged(CharSequence title, int color) {    TextView titleView = (TextView) mActivity.findViewById(R.id.actionbar_compat_title);    if (titleView != null) {      titleView.setText(title);    }  }  /**   * Returns a {@link android.view.MenuInflater} that can read action bar metadata on   * pre-Honeycomb devices.   */public MenuInflater getMenuInflater(MenuInflater superMenuInflater) {    return new WrappedMenuInflater(mActivity, superMenuInflater);  }  /**   * Returns the {@link android.view.ViewGroup} for the action bar on phones (compatibility action   * bar). Can return null, and will return null on Honeycomb.   */private ViewGroup getActionBarCompat() {    return (ViewGroup) mActivity.findViewById(R.id.actionbar_compat);  }  /**   * Adds an action button to the compatibility action bar, using menu information from a {@link* android.view.MenuItem}. If the menu item ID is <code>menu_refresh</code>, the menu item's   * state can be changed to show a loading spinner using   * {@link com.example.android.actionbarcompat.ActionBarHelperBase#setRefreshActionItemState(boolean)}.   */private View addActionItemCompatFromMenuItem(final MenuItem item) {    final int itemId = item.getItemId();    final ViewGroup actionBar = getActionBarCompat();    if (actionBar == null) {      return null;    }    // Create the buttonImageButton actionButton = new ImageButton(mActivity, null,        itemId == android.R.id.home? R.attr.actionbarCompatItemHomeStyle: R.attr.actionbarCompatItemStyle);    actionButton.setLayoutParams(new ViewGroup.LayoutParams(        (int) mActivity.getResources().getDimension(            itemId == android.R.id.home? R.dimen.actionbar_compat_button_home_width: R.dimen.actionbar_compat_button_width),        ViewGroup.LayoutParams.FILL_PARENT));    if (itemId == R.id.menu_refresh) {      actionButton.setId(R.id.actionbar_compat_item_refresh);    }    actionButton.setImageDrawable(item.getIcon());    actionButton.setScaleType(ImageView.ScaleType.CENTER);    actionButton.setContentDescription(item.getTitle());    actionButton.setOnClickListener(new View.OnClickListener() {      public void onClick(View view) {        mActivity.onMenuItemSelected(Window.FEATURE_OPTIONS_PANEL, item);      }    });    actionBar.addView(actionButton);    if (item.getItemId() == R.id.menu_refresh) {      // Refresh buttons should be stateful, and allow for indeterminate progress indicators,      // so add those.ProgressBar indicator = new ProgressBar(mActivity, null,          R.attr.actionbarCompatProgressIndicatorStyle);      final int buttonWidth = mActivity.getResources().getDimensionPixelSize(          R.dimen.actionbar_compat_button_width);      final int buttonHeight = mActivity.getResources().getDimensionPixelSize(          R.dimen.actionbar_compat_height);      final int progressIndicatorWidth = buttonWidth / 2;      LinearLayout.LayoutParams indicatorLayoutParams = new LinearLayout.LayoutParams(          progressIndicatorWidth, progressIndicatorWidth);      indicatorLayoutParams.setMargins(          (buttonWidth - progressIndicatorWidth) / 2,          (buttonHeight - progressIndicatorWidth) / 2,          (buttonWidth - progressIndicatorWidth) / 2,          0);      indicator.setLayoutParams(indicatorLayoutParams);      indicator.setVisibility(View.GONE);      indicator.setId(R.id.actionbar_compat_item_refresh_progress);      actionBar.addView(indicator);    }    return actionButton;  }  /**   * A {@link android.view.MenuInflater} that reads action bar metadata.   */private class WrappedMenuInflater extends MenuInflater {    MenuInflater mInflater;    public WrappedMenuInflater(Context context, MenuInflater inflater) {      super(context);      mInflater = inflater;    }    @Overridepublic void inflate(int menuRes, Menu menu) {      loadActionBarMetadata(menuRes);      mInflater.inflate(menuRes, menu);    }    /**     * Loads action bar metadata from a menu resource, storing a list of menu item IDs that     * should be shown on-screen (i.e. those with showAsAction set to always or ifRoom).*/private void loadActionBarMetadata(int menuResId) {      null;      try {        parser = mActivity.getResources().getint eventType = parser.getEventType();        int itemId;        int showAsAction;        boolean eof = false;        while (!eof) {          switch (eventType) {            case START_TAG:              if (!parser.getName().equals("item")) {                break;              }              itemId = parser.getAttributeResourceValue(MENU_RES_NAMESPACE,                  MENU_ATTR_ID, 0);              if (itemId == 0) {                break;              }              showAsAction = parser.getAttributeIntValue(MENU_RES_NAMESPACE,                  MENU_ATTR_SHOW_AS_ACTION, -1);              if (showAsAction == MenuItem.SHOW_AS_ACTION_ALWAYS ||                  showAsAction == MenuItem.SHOW_AS_ACTION_IF_ROOM) {                mActionItemIds.add(itemId);              }              break;            case END_DOCUMENT:              eof = true;              break;          }          eventType = parser.next();        }      } catch (throw new InflateException("Error inflating menu , e);      } catch (IOException e) {        throw new InflateException("Error inflating menu , e);      } finally {        if (parser != null) {          parser.close();        }      }    }  }}

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