Kotlin中的Wiki答案：

1-在文件中创建顶级函数（例如，包含所有顶级函数的文件）：

fun Activity.hideKeyboard(){
    val imm = this.getSystemService(Activity.INPUT_METHOD_SERVICE) as InputMethodManager
    var view = currentFocus
    if (view == null) { view = View(this) }
    imm.hideSoftInputFromWindow(view.windowToken, 0)
}

2-然后在你需要的任何活动中调用它：

this.hideKeyboard()

在如此的搜索中，我找到了一个适合我的答案

// Show soft-keyboard:
InputMethodManager imm = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
imm.toggleSoftInput(InputMethodManager.SHOW_FORCED, 0);

// Hide soft-keyboard:
getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);

Kotlin版本

val imm: InputMethodManager = getSystemService(Activity.INPUT_METHOD_SERVICE) as InputMethodManager
//Hide:
imm.toggleSoftInput(InputMethodManager.HIDE_IMPLICIT_ONLY, 0);
//Show
imm.toggleSoftInput(InputMethodManager.SHOW_IMPLICIT, 0);

使用这个

this.getWindow().setSoftInputMode(
            WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);

可以为任何视图创建Extension函数

fun View.hideKeyboard() = this.let {
    val imm = context.getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
    imm.hideSoftInputFromWindow(windowToken, 0)
}

与活动一起使用的示例

window.decorView.hideKeyboard();

与视图一起使用的示例

etUsername.hideKeyboard();

快乐编码。。。

/** 
 *
 *   Hide I Said!!!
 *
 */
public static boolean hideSoftKeyboard(@NonNull Activity activity) {
    View currentFocus = activity.getCurrentFocus();
    if (currentFocus == null) {
        currentFocus = activity.getWindow().getDecorView();
        if (currentFocus != null) {
            return getSoftInput(activity).hideSoftInputFromWindow(currentFocus.getWindowToken(), 0, null);
        }
    }
    return false;
}

public static boolean hideSoftKeyboard(@NonNull Context context) {
   if(Activity.class.isAssignableFrom(context.getClass())){
       return hideSoftKeyboard((Activity)context);
   }
   return false;
}

public static InputMethodManager getSoftInput(@NonNull Context context) {
    return (InputMethodManager) context.getSystemService(Activity.INPUT_METHOD_SERVICE);
}