[ Android 调试技巧 ] 为什么 content update 命令修改设置不生效？

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问题背景

开发以及定位问题的过程中，遇到 ContentProvider 相关的问题时，可以通过 adb shell content 的命令来进行调试。直接执行这个命令会在命令行打印它的用法（只截取了最常用的 update 和 query 的说明）：

> adb shell content
usage: adb shell content [subcommand] [options]

usage: adb shell content update --uri <URI> [--user <USER_ID>] [--where <WHERE>]
  <WHERE> is a SQL style where clause in quotes (You have to escape single quotes - see example below).
  Example:
  # Change "new_setting" secure setting to "newer_value".
  adb shell content update --uri content://settings/secure --bind value:s:newer_value --where "name='new_setting'"

usage: adb shell content query --uri <URI> [--user <USER_ID>] [--projection <PROJECTION>] [--where <WHERE>] [--sort <SORT_ORDER>]
  <PROJECTION> is a list of colon separated column names and is formatted:
  <COLUMN_NAME>[:<COLUMN_NAME>...]
  <SORT_ORDER> is the order in which rows in the result should be sorted.
  Example:
  # Select "name" and "value" columns from secure settings where "name" is equal to "new_setting" and sort the result by name in ascending order.
  adb shell content query --uri content://settings/secure --projection name:value --where "name='new_setting'" --sort "name ASC"

[ERROR] Unsupported operation: null

其中 query 用法很简单，直接对照实例说明修改一下就行了，比如查询屏幕超时时间：

XXX:/ # content query --uri content://settings/system --projection name:value --where "name='screen_off_timeout'"
Row: 0 name=screen_off_timeout, value=60000

但是执行 update 命令的时候遇到了麻烦，设置不生效：

XXX:/ # content update