Android code wiki

Android code wiki

Tip1:

类的全局静态变量的使用，这样可以静态变量只分配一次内存，可以不通过类的对象也就是可以通过类名直接使用该变量。（使用场景：Request_Code ,Result_Code,Log Tag,权限名字，Activity之间传递参数Name eg:bundle,公用参数名字,接受回调的参数( eg: getIntent() )，可以防止分配内存 etc）

/*
* Copyright (C) 2015 The Android Open Source Project
*
* 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.
*/

package com.android.cts.permissionapp;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;

import java.lang.Override;

/**
* A simple activity that requests permissions and returns the result.
*/
public class PermissionActivity extends Activity {
;

private String mPermission;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

final Intent received = getIntent();
Log.d(TAG, "Started with " + received);

final String action = received.getAction();
mPermission = received.getStringExtra(EXTRA_PERMISSION);
if (ACTION_REQUEST_PERMISSION.equals(action)) {
Log.d(TAG, "Requesting permission " + mPermission);
requestPermissions(new String[] {mPermission}, PERMISSIONS_REQUEST_CODE);
} else if (ACTION_CHECK_HAS_PERMISSION.equals(action)) {
Log.d(TAG, "Checking permission " + mPermission);
sendResultBroadcast(checkSelfPermission(mPermission));
} else {
Log.w(TAG, "Unknown intent received: " + received);
finish();
}
}

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions,
int[] grantResults) {
if (requestCode != PERMISSIONS_REQUEST_CODE ||
permissions.length != 1 ||
!permissions[].equals(mPermission)) {
Log.d(TAG, "Received wrong permissions result");
sendResultBroadcast(PERMISSION_ERROR);
} else {
Log.d(])]);
}
}

private void sendResultBroadcast(int result) {
Log.d(TAG, "Sending result broadcast: " + result);
Intent broadcast = new Intent(ACTION_PERMISSION_RESULT);
broadcast.putExtra(EXTRA_GRANT_STATE, result);
sendBroadcast(broadcast);
finish();
}
}

Tip 2:

namespace的小技巧，在Android 中最常用到的namespace 就是在XML里面的android:***，这样的写法非常方便，现在要说的不是android 这个namespace,是另外一个namespace tools.它非常有用。

tools的URI的全称是”http://schemas.android.com/tools”,常用的方式是声明整个URI以后用前缀 tools 来在XML文件里面使用。tools有关的所有属性不会影响应用的运行和应用的大小，所有的tools属性会被gradle 过滤掉的当编译打包的时候。

快速添加tools的步骤：

在XML的根里面添加，只要敲出 toolsNS 和 TAB (Android Studio)就会自动添加tools这个namespace的全URI.

tools使用方法：

Android Studio的XML里面现在还不提供对tools所有属性的自动补全，最简单的办法就是复制android:**，然后换一下namespace,把android 换成tools即可。

有时候为了开发方便而不影响用户的体验可以使用它，在XML里面声明一个TextView,但是为了预览更方便会设置android:text=“我是预览的文字，我一直在，不管是否编译”，这样就会预览到文字的效果，但是，如果只是在XML预览的时候能看到，编译运行以后就看不到，怎么实现呢？这时候就用到了tools这个神奇的工具，可以这样写tools:text="我是预览的文字，我不是一直在，编译我就消失啦” 来代替 android:text=“我是预览的文字，我一直在，不管是否编译”。

</LinearLayout>

同理，为了预览方便而编译以后不需要的时候任何场景都可以使用tools来实现。有时候为了预览的时候某些属性enable,但是运行的时候unenable。可以进行android namespace所有属性覆盖的，除了自定义View的属性。

</LinearLayout>

关于@TargetApi，在代码里面，经常会遇见的一个注解，用tools也是在XML里面可以实现的，比如：tools:targetApi,可以用integer 或者版本的名字来声明版本信息。

</LinearLayout>

当Lint检查 string resources是否正确的时候，经常会有警告信息，如果有强迫症并且应用没有走国际化，那么你可以这样来。

关于预览fragment或者自定义view。可以在一个布局文件里面这样写。下面是预览Booksfragment,不需要编译运行，也不需要模拟器就可以看到预览的效果啦。

</LinearLayout>

更复杂的多层级预览，也是可以达到的。比如预览一个Activity里面的一个fragment的一个ListView对应的每个Item，如果，不编译运行在模拟器或者自己的设备上，应该是看不到效果的，但是，有了tools，一切都变得简单了。

activity_main:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity">

</LinearLayout>

fragment_book:

（tools:listitem=“” tools:listheader，tools:listfooter，预览ListView是非常有用的，但是对于RecyclerView 没有header和footer）

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/list"
android:name="com.alexsimo.mastertoolsnamespace.BooksFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
app:layoutManager="LinearLayoutManager"
tools:context="com.alexsimo.mastertoolsnamespace.BooksFragment"
tools:listitem="@layout/fragment_book_list_item" />

fragment_book_list_item:

</LinearLayout>

这时候预览activity_main,如下：

关于预览layout 的 menus ,一般在Activity中定义 Activity.onCreateOptionsMenu()，为了预览可以用 tools:menu="comma separated menu IDs” ，设置Toolbar navigation mode,可以这样，tools:actionBarNavMode="standard|list|tabs”。

From: http://tools.android.com/tips/layout-designtime-attributes

Tip3:

关于软键盘的问题，常用的软键盘各种模式，比如，为了适应页面大小，可以android:windowSoftInputMode="adjustResize"

如果不喜欢XML配置，喜欢代码设置，那么你可以这样来：

activity.getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_ADJUST_RESIZE)

自定义View展示PDF文件，PDF文件可以编辑，那么view点击编辑状态，软键盘弹出，这时候设置adjustResize就无效了，因为这个页面是全屏的，关于Fullscreen mode,g官方解释是这样的：

If the window's layout parameter flags include FLAG_FULLSCREEN, this value for softInputMode will be ignored; the window will not resize, but will stay fullscreen.

总而言之和键盘的adjustResize冲突了，这时候键盘就出问题了。

这时候可以监听键盘，然后手动计算设置高度了。

// Threshold for minimal keyboard height.

final int MIN_KEYBOARD_HEIGHT_PX = 150;

// Top-level window decor view.

final View decorView = activity.getWindow().getDecorView();

// Register global layout listener.

decorView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {

private final Rect windowVisibleDisplayFrame = new Rect();

private int lastVisibleDecorViewHeight;

@Override

public void onGlobalLayout() {

// Retrieve visible rectangle inside window.

decorView.getWindowVisibleDisplayFrame(windowVisibleDisplayFrame);

final int visibleDecorViewHeight = windowVisibleDisplayFrame.height();

// Decide whether keyboard is visible from changing decor view height.

if (lastVisibleDecorViewHeight != 0) {

if (lastVisibleDecorViewHeight > visibleDecorViewHeight + MIN_KEYBOARD_HEIGHT_PX) {

// Calculate current keyboard height (this includes also navigation bar height when in fullscreen mode).

int currentKeyboardHeight = decorView.getHeight() - windowVisibleDisplayFrame.bottom;

// Notify listener about keyboard being shown.

listener.onKeyboardShown(currentKeyboardHeight);

} else if (lastVisibleDecorViewHeight + MIN_KEYBOARD_HEIGHT_PX < visibleDecorViewHeight) {

// Notify listener about keyboard being hidden.

listener.onKeyboardHidden();

}

// Save current decor view height for the next call.

lastVisibleDecorViewHeight = visibleDecorViewHeight;

}

});

From：https://pspdfkit.com/blog/2016/keyboard-handling-on-android/

Tip4: 关于遍历

在开发中，遍历集合，搜集信息，是最常见的代码块，遍历中，如果中间出现异常，是不是遍历就终止了，但是如果遍历出现异常还要能继续执行剩下的条目，怎么办呢，这时候就用到了异常处理机制，如下：

String routes = intent.getStringExtra(packageName + ".routes");

if (routes != null) {

String[] routeArray = routes.split(",");

for (int i = 0; i < routeArray.length; i++) {

String[] prefixAndMask = routeArray[i].split("/");

try {

InetAddress address = InetAddress.getByName(prefixAndMask[0]);

int prefixLength = Integer.parseInt(prefixAndMask[1]);

builder.addRoute(address, prefixLength);

} catch (UnknownHostException|NumberFormatException|

ArrayIndexOutOfBoundsException e) {

continue;

}

建议上面这种写法，catch捕获以后，continue；同时，关于异常的另外一个用处，当return用，可以直接返回，如下：

@Override

public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {

throw new RuntimeException("Operation not supported");

}

Tip5: 关于调用ShareCompat Intent，代码如下：

// Create share intent

Intent shareIntent = ShareCompat.IntentBuilder.from(this)

.setText(getShareText(coupon))

.setType("image/jpeg")

.setStream(coupon.mImageUri)

.setChooserTitle(getString(R.string.redeem_using))

.createChooserIntent();

startActivity(shareIntent);

关于格式化展示信息的时候，一般都是用String的format来进行，这里介绍另外一种：

if (TextUtils.isEmpty(SENDER_NAME)) {

return getString(R.string.message_format_without_sender,

coupon.mTitle, coupon.mSubtitle);

} else {

// Otherwise, use the other string template and pass in the {@link #SENDER_NAME} too

return getString(R.string.message_format_with_sender, SENDER_NAME,

coupon.mTitle, coupon.mSubtitle);

}

这里会调用Context里面的getString()方法来实现，前面的格式化的format如下，然后传入对于需要格式化的标题和子标题就OK了

<!--

Template string with coupon title, subtitle, and sender name for the text to use

when the coupon is shared with other apps. [CHAR LIMIT=NONE]

-->

<string name="message_format_without_sender">Excited to redeem my coupon! <xliff:g id="coupon_title">%s</xliff:g> - <xliff:g id="coupon_subtitle">%s</xliff:g> #justforus</string>

<!--

Template string with coupon title, subtitle, and sender name for the text to use

when the coupon is shared with other apps. [CHAR LIMIT=NONE] 写注释是个好习惯

-->

<string name="message_format_with_sender">Excited to redeem my coupon with <xliff:g id="coupon_title">%s</xliff:g>! <xliff:g id="coupon_title">%s</xliff:g> - <xliff:g id="coupon_subtitle">%s</xliff:g> #justforus</string>

</resources>

Tip5: 关于Adapter

/**

* Adapter for grid of coupons.

private static class CouponAdapter extends BaseAdapter {

private LayoutInflater mInflater;

private List<Coupon> mAllCoupons;

/**

* Constructs a new {@link CouponAdapter}.

* @param inflater to create new views

* @param allCoupons for list of all coupons to be displayed

public CouponAdapter(LayoutInflater inflater, List<Coupon> allCoupons) {

if (allCoupons == null) {

throw new IllegalStateException("Can't have null list of coupons");

}

mAllCoupons = allCoupons;

mInflater = inflater;

}

@Override

public int getCount() {

return mAllCoupons.size();

}

@Override

public Coupon getItem(int position) {

return mAllCoupons.get(position);

}

@Override

public long getItemId(int position) {

return position;

}

@Override

public View getView(int position, View convertView, ViewGroup parent) {

//缓存策略的另外一种写法

View result = convertView;

if (result == null) {

//注意mInflater的来源，是在Activity的setContextView中这样写的：

// Fetch the {@link LayoutInflater} service so that new views can be created

// LayoutInflater inflater = (LayoutInflater) getSystemService(

// Context.LAYOUT_INFLATER_SERVICE);

result = mInflater.inflate(R.layout.grid_item, parent, false);

}

// Try to get view cache or create a new one if needed

ViewCache viewCache = (ViewCache) result.getTag();

if (viewCache == null) {

viewCache = new ViewCache(result);

result.setTag(viewCache);

}

// Fetch item

Coupon coupon = getItem(position);

// Bind the data

viewCache.mTitleView.setText(coupon.mTitle);

viewCache.mSubtitleView.setText(coupon.mSubtitle);

viewCache.mImageView.setImageURI(coupon.mImageUri);

return result;

}

/**

* Cache of views in the grid item view to make recycling of views quicker. This avoids

* additional {@link View#findViewById(int)} calls after the {@link ViewCache} is first

* created for a view. See

* {@link CouponAdapter#getView(int position, View convertView, ViewGroup parent)}.

private static class ViewCache {

/** View that displays the title of the coupon */

private final TextView mTitleView;

/** View that displays the subtitle of the coupon */

private final TextView mSubtitleView;

/** View that displays the image associated with the coupon */

private final ImageView mImageView;

/**

* Constructs a new {@link ViewCache}.

* @param view which contains children views that should be cached.

private ViewCache(View view) {

mTitleView = (TextView) view.findViewById(R.id.title);

mSubtitleView = (TextView) view.findViewById(R.id.subtitle);

mImageView = (ImageView) view.findViewById(R.id.image);

}

/**

* 关于适配器里面数据bean对象问题，如果只是纯粹展示，而不需要改变bean对象的属性，那么推荐下面这种方式，如果需要改变

* bean对象的属性，那么还是用常见的get set方法实现.

private static class Coupon {

/** Title of the coupon. */

private final String mTitle;

/** Description of the coupon. */

private final String mSubtitle;

/** Content URI of the image for the coupon. */

private final Uri mImageUri;

/**

* Constructs a new {@link Coupon}.

* @param titleString is the title

* @param subtitleString is the description

* @param imageAssetFilePath is the file path from the application's assets folder for

* the image associated with this coupon

private Coupon(String titleString, String subtitleString, String imageAssetFilePath) {

mTitle = titleString;

mSubtitle = subtitleString;

mImageUri = Uri.parse("content://" + AssetProvider.CONTENT_URI + "/" +

imageAssetFilePath);

}

Tip6: 关于应用的全局常量

package com.example.android.apprestrictionenforcer;

public interface Constants {

/**

* Package name of the AppRestrictionSchema sample.

public static final String PACKAGE_NAME_APP_RESTRICTION_SCHEMA

= "com.example.android.apprestrictionschema";

}

为什么以接口的形式定义，而不用class定义呢，这里要说明一下用接口的好处，因为Java语言中要求，接口中定义的变量默认是public static final型，且必须给其初始值，所以实现类中不能重新定义，也不能改变其值，如果用到全局常量的定义的时候，这时候定义Constants，就限制了常量的类型，static final，多了一步校验。

题外话：接口更多的是在系统架构设计方法发挥作用，主要用于定义模块化之间的通信契约。（符合这种理念）

而抽象类在代码实现方面发挥作用，可以实现代码的重用。

Tip7: 关于网络

检查网络状态代码片：

/**

* Check whether the device is connected, and if so, whether the connection

* is wifi or mobile (it could be something else).

private void checkNetworkConnection() {

// BEGIN_INCLUDE(connect)

ConnectivityManager connMgr =

(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

NetworkInfo activeInfo = connMgr.getActiveNetworkInfo();

if (activeInfo != null && activeInfo.isConnected()) {

wifiConnected = activeInfo.getType() == ConnectivityManager.TYPE_WIFI;

mobileConnected = activeInfo.getType() == ConnectivityManager.TYPE_MOBILE;

if(wifiConnected) {

Log.i(TAG, getString(R.string.wifi_connection));

} else if (mobileConnected){

Log.i(TAG, getString(R.string.mobile_connection));

}

} else {

Log.i(TAG, getString(R.string.no_wifi_or_mobile));

}

// END_INCLUDE(connect)

}

获取屏幕的一切信息，来自这个类：

getResources().getDisplayMetrics() 得到

DisplayMetrics 这个类，就可以获取到一切有关设备屏幕大小，密度等信息了...

// eg: Calculate radiuses in px from dp based on screen density
float density = getResources().getDisplayMetrics().density;

关于自定义View中随机颜色的写法：

定义十六进制的颜色

public final int[] COLORS = {
0xFF33B5E5, 0xFFAA66CC, 0xFF99CC00, 0xFFFFBB33, 0xFFFF4444,
0xFF0099CC, 0xFF9933CC, 0xFF669900, 0xFFFF8800, 0xFFCC0000

};

这样就可以根据id动态获取到颜色了

int color = COLORS[id % COLORS.length];

设置背景

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN)
setBackground(states);
else
setBackgroundDrawable(states);

Tip7: 关于Build

apply plugin: 'com.android.application'

def getGitVersion() {
try {
return 'git rev-parse --short HEAD'.execute().text.trim()
} catch (Throwable th) {
return "";
}
}

android {
compileSdkVersion 23
buildToolsVersion buildToolsVer
useLibrary 'org.apache.http.legacy'

defaultConfig {
minSdkVersion 9
targetSdkVersion 23
buildConfigField "String", "GIT_REVISION", "\"${getGitVersion()}\""
buildConfigField "String", "BUILD_DATE", "\"${new Date().toLocaleString()}\"";
}

signingConfigs {
debug { storeFile file("debug.keystore") }

release {
storeFile file('release.keystore')
storePassword 'thisiskeystorepassword'
keyAlias 'nim_demo'
keyPassword 'thisiskeypassword'
}
}

buildTypes {
debug {
signingConfig signingConfigs.debug
manifestPlaceholders = [ AMAP_KEY:"09fd4efd3e28e9bf1f449ecec7d34bfe" ]
}

release {
minifyEnabled true
zipAlignEnabled true
proguardFile('proguard.cfg')
signingConfig signingConfigs.release
manifestPlaceholders = [ AMAP_KEY:"ee20324fba1c7f4ad7a4a207e7f08e8d" ]
}
}
sourceSets {
main {
manifest.srcFile 'AndroidManifest.xml'
java.srcDirs = ['src']
resources.srcDirs = ['src']
aidl.srcDirs = ['src']
renderscript.srcDirs = ['src']
res.srcDirs = ['res', 'res-avchat', 'res-chatroom']
assets.srcDirs = ['assets']
jniLibs.srcDirs = ['libs', 'libs-sdk']

}

lintOptions {
checkReleaseBuilds false
abortOnError false
}
dexOptions {
incremental true
preDexLibraries false
jumboMode true
}
packagingOptions {
exclude 'META-INF/LICENSE.txt'
exclude 'META-INF/NOTICE.txt'
}

}

dependencies {
compile fileTree(dir: 'libs', include: '*.jar', exclude: ['android-support-*.jar'])
compile project(path: ':uikit')
}

在Activity中引用build中定义的变量：

在AndroidMainfest.xml中引用配置的key:

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