Android开发Tips(5)

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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.

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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]

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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.

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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
                    }
                }
        );

參考和參考.

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4. Chrome的JsonView插件

加入插件之后, 能够格式化的显示Json数据.

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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}

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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.

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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.

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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);
    }
}

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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.

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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);

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OK, that’s all! Enjoy it!