Android開發Tips(5)

---

1. 模擬系統回收Activity.

使用adb命令可以模擬Android系統自動回收Activity進程, 可以調試這個效果.
單進程

adb shell am force-stop [包名]

多進程

adb shell ps | grep [包名]
adb shell kill [PID]

---

2. Android庫動態權限建議

Android 6.0使用動態權限, 在創建第三方庫時, 需要充分考慮這一特性.
(1) 在自動Merge庫的AndroidManifest時, 需要提供危險權限的提示文檔.
(2) 當權限未獲取時, 用戶可以使用庫的某一部分, 並提示缺少權限.
(3) 需要提供在權限獲取失敗時, 庫使用方式的文檔.
(4) 確保所有權限都是必須的, 不含有未使用權限.

關於提示用戶獲取權限的解決方案, 可以參考.

---

3. RxJava處理Retry請求服務器

服務器經常會出現異常, 應用需要連續嘗試請求, RxJava可以非常簡單的實現.

模板

Observable 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>() {
            @Override
            public Observable call(Observable 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() {
            @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() {
            @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() {
                    @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.

---

4. Chrome的JsonView插件

添加插件之後, 可以格式化的顯示Json數據.

---

5. 顯示Activity棧的Shell命令

Shell命令

adb shell dumpsys activity | sed -n -e '/Stack #/p' -e '/Running activities/,/Run #0/p'

直接獲取Activity信息有些冗余, 我們只關注堆棧信息即可.
sed可以編輯顯示的文字.
-n, 從截取處開始連續處理.
-e, 多選參數.
'/Stack #/p', 輸出含有Stack #的行.
-e '/Running activities/,/Run #0/p', 輸出從Running activities至Run #0的所有行.

輸出結果

  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的區別

dp是Android頁面常用的度量單位, sp主要用於字體度量.
在標准情況下, dp等於sp. 然而, Android系統允許用戶設置字體大小, sp會隨著字體的大小而改變, 放大或是縮小.
設置位置(紅米): Android -> 設置 -> 字體大小 -> 標准(默認)或大小號.

---

7. AlertDialog獲取全部屏幕監聽

在Android 4.0以上, AlertDialog在觸摸對話框邊緣外部時, 對話框消失.
在AlertDialog.Builder.create(), 可以設置屬性獲取屏幕監聽.
方法一:

setCanceledOnTouchOutside(false);

調用這個方法時, 按對話框以外的地方不起作用. 按返回鍵仍起作用.

方法二:

setCancelable(false);

調用這個方法時, 按對話框以外的地方不起作用. 按返回鍵也不起作用.

---

8. getColor遺棄

最新版本的getColor被遺棄(deprecated), 使用時, 需要添加主題.
也可以使用兼容模式, 即

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

ContextCompat.getColor的源碼

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簡介

libarchive
Multi-format archive and compression library. 多格式存檔和壓縮庫.
Android的toolchain使用libArchive.
參考

expat
Expat is an XML parser library written in C. Expat是用C語言寫的XML解析庫.
Android的Platform的擴展.
參考

libarchive 2.8.4和expat 2.1.0會產生漏洞, 如需修復, 需要升級Android的編譯版本.

---

10. 網頁重定向

默認鏈接會跳轉其他鏈接, 根據鏈接內容, 進行相應操作, 如下載Apk等. 如果使用重定向, 則返回false; 如果非重定向, 則返回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!