Android开发Tips(5)

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本文的合集已经编著成书，高级Android开发强化实战，欢迎各位读友的建议和指导。在京东即可购买：https://item.jd.com/12385680.html

1. 模拟系统回收Activity.

使用adb命令可以模拟Android系统自动回收Activity进程, 可以调试这个效果.
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, 需要充分考虑这一特性.
(1) 在自动Merge库的AndroidManifest时, 需要提供危险权限的提示文档.
(2) 当权限未获取时, 用户可以使用库的某一部分, 并提示缺少权限.
(3) 需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案, 可以参考.

3. RxJava处理Retry请求服务器

服务器经常会出现异常, 应用需要连续尝试请求, RxJava可以非常简单的实现.

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()")
    );

示例

/**
 * 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
                    }
                }
        );

参考和参考.

4. Chrome的JsonView插件

添加插件之后, 可以格式化的显示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, 我们只关注堆栈信息即可.
sed可以编辑显示的文字.
-n, 从截取处开始连续处理.
-e, 多选参数.
'/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的区别

dp是Android页面常用的度量单位, sp主要用于字体度量.
在标准情况下, dp等于sp. 然而, Android系统允许用户设置字体大小, 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获取全部屏幕监听

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(), 可以设置属性获取屏幕监听.
方法一:

setCanceledOnTouchOutside(false);

调用这个方法时, 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);

调用这个方法时, 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

最新版本的getColor被遗弃(deprecated), 使用时, 需要添加主题.
也可以使用兼容模式, 即

ContextCompat.getColor(context, R.color.your_color);

ContextCompat.getColor的源码

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简介

libarchive
Multi-format archive and compression library. 多格式存档和压缩库.
Android的toolchain使用libArchive.
参考

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.
参考

libarchive 2.8.4和expat 2.1.0会产生漏洞, 如需修复, 需要升级Android的编译版本.

10. 网页重定向

默认链接会跳转其他链接, 根据链接内容, 进行相应操作, 如下载Apk等. 如果使用重定向, 则返回false; 如果非重定向, 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!