Android基类设计方法详解
1 为什么要设计基类
为什么要给程序设计基类呢?主要是出于2个原因,一是方便代码编写,减少重复代码和冗余逻辑,优化代码;二是优化程序架构,降低耦合度,方便拓展、修改。
ok,编写代码是程序员的第一步,那么第二步就是要编写高质量的代码,代码能实现功能是一方面,写的优美则是另一方面,这也是我们所有攻城狮们应该追求的境界。
2 设计基类的基本思路
那么,哪些东西我们需要抽象到基类中呢?
2.1 重复的代码:如果一个逻辑是大多数子类都需要使用的
2.2 臭而长的代码:典型的findviewbyid、Toast
2.3 需要修改原生行为的:要改变某控件的样式
2.4 为子类创建标准流程模板:模板设计模式
2.5 常用的方法:转换dip、px
3 常用基类的设计实例
public abstract class BaseActivity extends Activity { protected int mScreenWidth; protected int mScreenHeight; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // 公共属性 DisplayMetrics metric = new DisplayMetrics(); getWindowManager().getDefaultDisplay().getMetrics(metric); mScreenWidth = metric.widthPixels; mScreenHeight = metric.heightPixels; // 定制流程 setContentView(); initViews(); initListeners(); initData(); } Toast mToast; public abstract void setContentView(); public abstract void initViews(); public abstract void initListeners(); public abstract void initData(); // 常用方法 public void ShowToast(String text) { if (!TextUtils.isEmpty(text)) { if (mToast == null) { mToast = Toast.makeText(getApplicationContext(), text, Toast.LENGTH_SHORT); } else { mToast.setText(text); } mToast.show(); } } // 常用方法 public int getStateBar() { Rect frame = new Rect(); getWindow().getDecorView().getWindowVisibleDisplayFrame(frame); int statusBarHeight = frame.top; return statusBarHeight; } // 常用方法 public static int dip2px(Context context, float dipValue) { float scale = context.getResources().getDisplayMetrics().density; return (int) (scale * dipValue + 0.5f); } }
3.2 BaseAdapter
/** * Copyright 2013 Joan Zapata * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import android.annotation.TargetApi; import android.content.Context; import android.graphics.Bitmap; import android.graphics.Typeface; import android.graphics.drawable.Drawable; import android.os.Build; import android.text.util.Linkify; import android.util.SparseArray; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.view.animation.AlphaAnimation; import android.widget.ImageView; import android.widget.ProgressBar; import android.widget.RatingBar; import android.widget.TextView; import com.squareup.picasso.Picasso; import com.squareup.picasso.RequestCreator; /** * Allows an abstraction of the ViewHolder pattern.<br> * <br> * <p/> * <b>Usage</b> * <p/> * <pre> * return BaseAdapterHelper.get(context, convertView, parent, R.layout.item) * .setText(R.id.tvName, contact.getName()) * .setText(R.id.tvEmails, contact.getEmails().toString()) * .setText(R.id.tvNumbers, contact.getNumbers().toString()) * .getView(); * </pre> */ @TargetApi(Build.VERSION_CODES.HONEYCOMB) public class BaseAdapterHelper { /** Views indexed with their IDs */ private final SparseArray<View> views; private final Context context; private int position; private View convertView; private BaseAdapterHelper(Context context, ViewGroup parent, int layoutId, int position) { this.context = context; this.position = position; this.views = new SparseArray<View>(); convertView = LayoutInflater.from(context) // .inflate(layoutId, parent, false); convertView.setTag(this); } /** * This method is the only entry point to get a BaseAdapterHelper. * @param context The current context. * @param convertView The convertView arg passed to the getView() method. * @param parent The parent arg passed to the getView() method. * @return A BaseAdapterHelper instance. */ public static BaseAdapterHelper get(Context context, View convertView, ViewGroup parent, int layoutId) { return get(context, convertView, parent, layoutId, -1); } /** This method is package private and should only be used by QuickAdapter. */ static BaseAdapterHelper get(Context context, View convertView, ViewGroup parent, int layoutId, int position) { if (convertView == null) { return new BaseAdapterHelper(context, parent, layoutId, position); } return (BaseAdapterHelper) convertView.getTag(); } /** * This method allows you to retrieve a view and perform custom * operations on it, not covered by the BaseAdapterHelper.<br/> * If you think it‘s a common use case, please consider creating * a new issue at https://github.com/JoanZapata/base-adapter-helper/issues. * @param viewId The id of the view you want to retrieve. */ public <T extends View> T getView(int viewId) { return retrieveView(viewId); } /** * Will set the text of a TextView. * @param viewId The view id. * @param value The text to put in the text view. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setText(int viewId, String value) { TextView view = retrieveView(viewId); view.setText(value); return this; } /** * Will set the image of an ImageView from a resource id. * @param viewId The view id. * @param imageResId The image resource id. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setImageResource(int viewId, int imageResId) { ImageView view = retrieveView(viewId); view.setImageResource(imageResId); return this; } /** * Will set background color of a view. * @param viewId The view id. * @param color A color, not a resource id. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setBackgroundColor(int viewId, int color) { View view = retrieveView(viewId); view.setBackgroundColor(color); return this; } /** * Will set background of a view. * @param viewId The view id. * @param backgroundRes A resource to use as a background. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setBackgroundRes(int viewId, int backgroundRes) { View view = retrieveView(viewId); view.setBackgroundResource(backgroundRes); return this; } /** * Will set text color of a TextView. * @param viewId The view id. * @param textColor The text color (not a resource id). * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setTextColor(int viewId, int textColor) { TextView view = retrieveView(viewId); view.setTextColor(textColor); return this; } /** * Will set the image of an ImageView from a drawable. * @param viewId The view id. * @param drawable The image drawable. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setImageDrawable(int viewId, Drawable drawable) { ImageView view = retrieveView(viewId); view.setImageDrawable(drawable); return this; } /** * Will download an image from a URL and put it in an ImageView.<br/> * It uses Square‘s Picasso library to download the image asynchronously and put the result into the ImageView.<br/> * Picasso manages recycling of views in a ListView.<br/> * If you need more control over the Picasso settings, use {BaseAdapterHelper#setImageBuilder}. * @param viewId The view id. * @param imageUrl The image URL. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setImageUrl(int viewId, String imageUrl) { ImageView view = retrieveView(viewId); Picasso.with(context).load(imageUrl).into(view); return this; } /** * Will download an image from a URL and put it in an ImageView.<br/> * @param viewId The view id. * @param requestBuilder The Picasso request builder. (e.g. Picasso.with(context).load(imageUrl)) * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setImageBuilder(int viewId, RequestCreator requestBuilder) { ImageView view = retrieveView(viewId); requestBuilder.into(view); return this; } /** Add an action to set the image of an image view. Can be called multiple times. */ public BaseAdapterHelper setImageBitmap(int viewId, Bitmap bitmap) { ImageView view = retrieveView(viewId); view.setImageBitmap(bitmap); return this; } /** * Add an action to set the alpha of a view. Can be called multiple times. * Alpha between 0-1. */ public BaseAdapterHelper setAlpha(int viewId, float value) { if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { retrieveView(viewId).setAlpha(value); } else { // Pre-honeycomb hack to set Alpha value AlphaAnimation alpha = new AlphaAnimation(value, value); alpha.setDuration(0); alpha.setFillAfter(true); retrieveView(viewId).startAnimation(alpha); } return this; } /** * Set a view visibility to VISIBLE (true) or GONE (false). * @param viewId The view id. * @param visible True for VISIBLE, false for GONE. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setVisible(int viewId, boolean visible) { View view = retrieveView(viewId); view.setVisibility(visible ? View.VISIBLE : View.GONE); return this; } /** * Add links into a TextView. * @param viewId The id of the TextView to linkify. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper linkify(int viewId) { TextView view = retrieveView(viewId); Linkify.addLinks(view, Linkify.ALL); return this; } /** Apply the typeface to the given viewId */ public BaseAdapterHelper setTypeface(int viewId, Typeface typeface) { TextView view = retrieveView(viewId); view.setTypeface(typeface); return this; } /** Apply the typeface to all the given viewIds */ public BaseAdapterHelper setTypeface(Typeface typeface, int... viewIds) { for (int viewId : viewIds) { TextView view = retrieveView(viewId); view.setTypeface(typeface); } return this; } /** * Sets the progress of a ProgressBar. * @param viewId The view id. * @param progress The progress. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setProgress(int viewId, int progress) { ProgressBar view = retrieveView(viewId); view.setProgress(progress); return this; } /** * Sets the progress and max of a ProgressBar. * @param viewId The view id. * @param progress The progress. * @param max The max value of a ProgressBar. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setProgress(int viewId, int progress, int max) { ProgressBar view = retrieveView(viewId); view.setProgress(progress); view.setMax(max); return this; } /** * Sets the range of a ProgressBar to 0...max. * @param viewId The view id. * @param max The max value of a ProgressBar. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setMax(int viewId, int max) { ProgressBar view = retrieveView(viewId); view.setMax(max); return this; } /** * Sets the rating (the number of stars filled) of a RatingBar. * @param viewId The view id. * @param rating The rating. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setRating(int viewId, float rating) { RatingBar view = retrieveView(viewId); view.setRating(rating); return this; } /** * Sets the rating (the number of stars filled) and max of a RatingBar. * @param viewId The view id. * @param rating The rating. * @param max The range of the RatingBar to 0...max. * @return The BaseAdapterHelper for chaining. */ public BaseAdapterHelper setRating(int viewId, float rating, int max) { RatingBar view = retrieveView(viewId); view.setRating(rating); view.setMax(max); return this; } /** Retrieve the convertView */ public View getView() { return convertView; } /** * Retrieve the overall position of the data in the list. * @throws IllegalArgumentException If the position hasn‘t been set at the construction of the this helper. */ public int getPosition() { if (position == -1) throw new IllegalStateException("Use BaseAdapterHelper constructor " + "with position if you need to retrieve the position."); return position; } @SuppressWarnings("unchecked") private <T extends View> T retrieveView(int viewId) { View view = views.get(viewId); if (view == null) { view = convertView.findViewById(viewId); views.put(viewId, view); } return (T) view; } }
如何使用呢:
/** * Copyright 2013 Joan Zapata * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import android.content.Context; import android.view.Gravity; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.FrameLayout; import android.widget.ProgressBar; import java.util.ArrayList; import java.util.List; /** * Abstraction class of a BaseAdapter in which you only need * to provide the convert() implementation.<br/> * Using the provided BaseAdapterHelper, your code is minimalist. * @param <T> The type of the items in the list. */ public abstract class BaseQuickAdapter<T, H extends BaseAdapterHelper> extends BaseAdapter { protected static final String TAG = BaseQuickAdapter.class.getSimpleName(); protected final Context context; protected final int layoutResId; protected final List<T> data; protected boolean displayIndeterminateProgress = false; /** * Create a QuickAdapter. * @param context The context. * @param layoutResId The layout resource id of each item. */ public BaseQuickAdapter(Context context, int layoutResId) { this(context, layoutResId, null); } /** * Same as QuickAdapter#QuickAdapter(Context,int) but with * some initialization data. * @param context The context. * @param layoutResId The layout resource id of each item. * @param data A new list is created out of this one to avoid mutable list */ public BaseQuickAdapter(Context context, int layoutResId, List<T> data) { this.data = data == null ? new ArrayList<T>() : new ArrayList<T>(data); this.context = context; this.layoutResId = layoutResId; } @Override public int getCount() { int extra = displayIndeterminateProgress ? 1 : 0; return data.size() + extra; } @Override public T getItem(int position) { if (position >= data.size()) return null; return data.get(position); } @Override public long getItemId(int position) { return position; } @Override public int getViewTypeCount() { return 2; } @Override public int getItemViewType(int position) { return position >= data.size() ? 1 : 0; } @Override public View getView(int position, View convertView, ViewGroup parent) { if (getItemViewType(position) == 0) { final H helper = getAdapterHelper(position, convertView, parent); convert(helper, getItem(position)); return helper.getView(); } return createIndeterminateProgressView(convertView, parent); } private View createIndeterminateProgressView(View convertView, ViewGroup parent) { if (convertView == null) { FrameLayout container = new FrameLayout(context); container.setForegroundGravity(Gravity.CENTER); ProgressBar progress = new ProgressBar(context); container.addView(progress); convertView = container; } return convertView; } @Override public boolean isEnabled(int position) { return position < data.size(); } public void add(T elem) { data.add(elem); notifyDataSetChanged(); } public void addAll(List<T> elem) { data.addAll(elem); notifyDataSetChanged(); } public void set(T oldElem, T newElem) { set(data.indexOf(oldElem), newElem); } public void set(int index, T elem) { data.set(index, elem); notifyDataSetChanged(); } public void remove(T elem) { data.remove(elem); notifyDataSetChanged(); } public void remove(int index) { data.remove(index); notifyDataSetChanged(); } public boolean contains(T elem) { return data.contains(elem); } /** Clear data list */ public void clear() { data.clear(); notifyDataSetChanged(); } public void showIndeterminateProgress(boolean display) { if (display == displayIndeterminateProgress) return; displayIndeterminateProgress = display; notifyDataSetChanged(); } /** * Implement this method and use the helper to adapt the view to the given item. * @param helper A fully initialized helper. * @param item The item that needs to be displayed. */ protected abstract void convert(H helper, T item); /** * You can override this method to use a custom BaseAdapterHelper in order to fit your needs * * @param position The position of the item within the adapter‘s data set of the item whose view we want. * @param convertView The old view to reuse, if possible. Note: You should check that this view * is non-null and of an appropriate type before using. If it is not possible to convert * this view to display the correct data, this method can create a new view. * Heterogeneous lists can specify their number of view types, so that this View is * always of the right type (see {@link #getViewTypeCount()} and * {@link #getItemViewType(int)}). * @param parent The parent that this view will eventually be attached to * @return An instance of BaseAdapterHelper */ protected abstract H getAdapterHelper(int position, View convertView, ViewGroup parent); }
最后再看下我们在设置adapter的时候如何使用:
/** * Copyright 2013 Joan Zapata * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import java.util.List; import android.content.Context; import android.view.View; import android.view.ViewGroup; import static com.bmob.lostfound.adapter.BaseAdapterHelper.get; /** * Abstraction class of a BaseAdapter in which you only need * to provide the convert() implementation.<br/> * Using the provided BaseAdapterHelper, your code is minimalist. * @param <T> The type of the items in the list. */ public abstract class QuickAdapter<T> extends BaseQuickAdapter<T, BaseAdapterHelper> { /** * Create a QuickAdapter. * @param context The context. * @param layoutResId The layout resource id of each item. */ public QuickAdapter(Context context, int layoutResId) { super(context, layoutResId); } /** * Same as QuickAdapter#QuickAdapter(Context,int) but with * some initialization data. * @param context The context. * @param layoutResId The layout resource id of each item. * @param data A new list is created out of this one to avoid mutable list */ public QuickAdapter(Context context, int layoutResId, List<T> data) { super(context,layoutResId,data); } protected BaseAdapterHelper getAdapterHelper(int position, View convertView, ViewGroup parent) { return get(context, convertView, parent, layoutResId, position); } }
是不算少写很多代码,也许有人会说你写前面那么多代码,比你后面少写的还要多。确实,但是你忽略了一点就是上面的基类是通用的,也就是说,你一句话不用改就可以在其他项目中用了,你的程序员生涯就再也不用写那么多adapter了。
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