Great question! Let's break this down clearly based on Android's system constraints and practical workarounds:

一、无Root权限的情况 #

Unfortunately, you can't manually resize arbitrary third-party app windows without root access using standard Android APIs. Here's why:

• Android's native framework restricts third-party apps from modifying other apps' window parameters for security and system stability. Features like Samsung's floating window are custom extensions built into their ROM at the framework level—these aren't exposed to third-party developers via public APIs.
• The only exception is if you control the app's source code: you can adjust your own app's window size using WindowManager.LayoutParams within the app itself. For example:

  WindowManager.LayoutParams params = getWindow().getAttributes();
  params.width = 800; // 自定义宽度（像素）
  params.height = 600; // 自定义高度（像素）
  getWindow().setAttributes(params);
  

  But this only works for your own app, not other installed apps.
• Android's native split-screen mode is available, but it's user-initiated—third-party apps can't force other apps into split-screen or adjust their ratios programmatically, even if the target app supports split-screen.

二、有Root权限的情况 #

With root access, you can achieve this via Java code without modifying the system itself, by tapping into Android's internal window management APIs. Here's how:

• You can use reflection to access the system's WindowManagerService and modify the target app's window parameters. Alternatively, you can execute system commands via Runtime.getRuntime().exec() (using root privileges) to adjust window attributes.
• A high-level code outline would look like this:
  1. Request root access for your app.
  2. Identify the target app's package name and its active window ID (you can get this via system logs or using ActivityManager with root).
  3. Use reflection to retrieve the WindowManagerService instance, then locate the WindowState object corresponding to the target window.
  4. Modify the mFrame or LayoutParams fields of the WindowState to set your desired width and height.
  5. Trigger a window update to apply the changes.
• Important notes:
  • This relies on Android's internal, unpublicized APIs, which can change between Android versions (e.g., Android 10 vs. Android 14). Your code will need version-specific adaptations.
  • Mishandling window parameters can cause system UI glitches or app crashes, so thorough testing is essential.

内容的提问来源于stack exchange，提问作者miversen33