介绍关于Android的一些有趣的小知识点. 本文是第五篇了, 差点儿一周一篇, 欢迎阅读.
其余第一篇, 第二篇, 第三篇, 第四篇.
1. 模拟系统回收Activity.
使用adb命令能够模拟Android系统自己主动回收Activity进程, 能够调试这个效果.
单进程
adb shell am force-stop [包名]多进程
adb shell ps | grep [包名]
adb shell kill [PID]2. Android库动态权限建议
Android 6.0使用动态权限, 在创建第三方库时, 须要充分考虑这一特性.
(1) 在自己主动Merge库的AndroidManifest时, 须要提供危急权限的提示文档.
(2) 当权限未获取时, 用户能够使用库的某一部分, 并提示缺少权限.
(3) 须要提供在权限获取失败时, 库使用方式的文档.
(4) 确保所有权限都是必须的, 不含有未使用权限.
关于提示用户获取权限的解决方式, 能够參考.
3. RxJava处理Retry请求服务器
服务器经常会出现异常, 应用须要连续尝试请求, RxJava能够很easy的实现.
模板
Observable<Boolean> source = ...; // Something that eventually emits true
source
.repeatWhen(completed -> completed.delay(1, TimeUnit.SECONDS))
.takeUntil(result -> result)
.filter(result -> result)
.subscribe(
res -> System.out.println("onNext(" + res + ")"),
err -> System.out.println("onError()"),
() -> System.out.println("onCompleted()")
);演示样例
/**
* This is a class that should be
* mapped on your json response from the server
*/
class ServerPollingResponse {
boolean isJobDone;
@Override
public String toString() {
return "isJobDone=" + isJobDone;
}
}
Subscription checkJobSubscription = mDataManager.pollServer(inputData)
.repeatWhen(new Func1<Observable<?
extends Void>, Observable<?>>() {
@Override
public Observable<?> call(Observable<?
extends Void> observable) {
Log.v(TAG, "repeatWhen, call");
/**
* This is called only once.
* 5 means each repeated call will be delayed by 5 seconds
*/
return observable.delay(5, TimeUnit.SECONDS);
}
})
.takeUntil(new Func1<ServerPollingResponse, Boolean>() {
@Override
public Boolean call(ServerPollingResponse response) {
/** Here we can check if the responce is correct and if we should
* finish polling
* We finish polling when job is done.
* In other words : "We stop taking when job is done"
*/
Log.v(TAG, "takeUntil, call response " + response);
return response.isJobDone;
}
})
.filter(new Func1<ServerPollingResponse, Boolean>() {
@Override
public Boolean call(ServerPollingResponse response) {
/**
* We are filtering results if we return "false".
* Filtering means that onNext() will not be called.
* But onComplete() will be delivered.
*/
Log.v(TAG, "filter, call response " + response);
return response.isJobDone;
}
})
.subscribe(
new Subscriber<ServerPollingResponse>() {
@Override
public void onCompleted() {
Log.v(TAG, "onCompleted ");
}
@Override
public void onError(Throwable e) {
Log.v(TAG, "onError ");
}
@Override
public void onNext(ServerPollingResponse response) {
Log.v(TAG, "onNext response " + response);
// Do whatever you need. Server polling has been finished
}
}
);4. Chrome的JsonView插件
加入插件之后, 能够格式化的显示Json数据.
5. 显示Activity栈的Shell命令
Shell命令
adb shell dumpsys activity | sed -n -e '/Stack #/p' -e '/Running activities/,/Run #0/p'直接获取Activity信息有些冗余, 我们仅仅关注堆栈信息就可以.
sed能够编辑显示的文字. -n, 从截取处開始连续处理. -e, 多选參数. '/Stack #/p', 输出含有Stack #的行. -e '/Running activities/,/Run #0/p', 输出从Running activities至Run #0的所有行.
输出结果
Stack #1:
Running activities (most recent first):
TaskRecord{299f41ea #2269 A=me.chunyu.spike.wcl_activity_launchmode_demo U=0 sz=6}
Run #5: ActivityRecord{33926043 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2269}
Run #4: ActivityRecord{3f181566 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2269}
Run #3: ActivityRecord{22737e45 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2269}
Run #2: ActivityRecord{ce0a990 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2269}
Run #1: ActivityRecord{3de8e378 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2269}
Run #0: ActivityRecord{1cb28ec4 u0 me.chunyu.spike.wcl_activity_launchmode_demo/.MainActivity t2269}
Stack #0:
Running activities (most recent first):
TaskRecord{bfee9cf #2241 A=com.miui.home U=0 sz=1}
Run #0: ActivityRecord{279bc098 u0 com.miui.home/.launcher.Launcher t2241}6. dp和sp的差别
dp是Android页面经常使用的度量单位, sp主要用于字体度量.
在标准情况下, dp等于sp. 然而, Android系统同意用户设置字体大小, sp会随着字体的大小而改变, 放大或是缩小.
设置位置(红米): Android -> 设置 -> 字体大小 -> 标准(默认)或大小号.
7. AlertDialog获取所有屏幕监听
在Android 4.0以上, AlertDialog在触摸对话框边缘外部时, 对话框消失.
在AlertDialog.Builder.create(), 能够设置属性获取屏幕监听.
方法一:
setCanceledOnTouchOutside(false);调用这种方法时, 按对话框以外的地方不起作用. 按返回键仍起作用.
方法二:
setCancelable(false);调用这种方法时, 按对话框以外的地方不起作用. 按返回键也不起作用.
8. getColor遗弃
最新版本号的getColor被遗弃(deprecated), 使用时, 须要加入主题.
也能够使用兼容模式, 即
ContextCompat.getColor(context, R.color.your_color);ContextCompat.getColor的源代码
public static final int getColor(Context context, int id) {
final int version = Build.VERSION.SDK_INT;
if (version >= 23) {
return ContextCompatApi23.getColor(context, id);
} else {
return context.getResources().getColor(id);
}
}9. libarchive和expat简单介绍
libarchive
Multi-format archive and compression library. 多格式存档和压缩库.
Android的toolchain使用libArchive.
參考
expat
Expat is an XML parser library written in C. Expat是用C语言写的XML解析库.
Android的Platform的扩展.
參考
libarchive 2.8.4和expat 2.1.0会产生漏洞, 如需修复, 须要升级Android的编译版本号.
10. 网页重定向
默认链接会跳转其它链接, 依据链接内容, 进行对应操作, 例如以下载Apk等. 假设使用重定向, 则返回false; 假设非重定向, 则返回true.
WebViewClient webClient = new WebViewClient() {
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
if (url.endsWith(".apk")) {
DownloadUtils.downloadFiles(url);
if (mStartDownloadAppListener != null) {
mStartDownloadAppListener.doAfter();
}
return true;
}
return false;
}
};
setWebViewClient(webClient);OK, that’s all! Enjoy it!