• 效果
  

• 源码实现

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

public final void showSafeModeOverlay() {
    View v = LayoutInflater.from(mContext).inflate(
            com.android.internal.R.layout.safe_mode, null);
    WindowManager.LayoutParams lp = new WindowManager.LayoutParams();
    lp.type = WindowManager.LayoutParams.TYPE_SECURE_SYSTEM_OVERLAY;
    lp.width = WindowManager.LayoutParams.WRAP_CONTENT;
    lp.height = WindowManager.LayoutParams.WRAP_CONTENT;
    //lp.gravity = Gravity.BOTTOM | Gravity.START;
    //修改为居中显示
    lp.gravity = Gravity.CENTER;
    lp.format = v.getBackground().getOpacity();
    lp.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
            | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
    lp.privateFlags |= WindowManager.LayoutParams.SYSTEM_FLAG_SHOW_FOR_ALL_USERS;
    ((WindowManager)mContext.getSystemService(
            Context.WINDOW_SERVICE)).addView(v, lp);
}

• 源码调用

frameworks/base/services/java/com/android/server/SystemServer.java

	//if(safeMode){//默认设置为安全模式
	  mActivityManagerService.showSafeModeOverlay();
	//}

• 布局

frameworks/base/core/res/res/layout/safe_mode.xml

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content" android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:gravity="center"
    android:padding="3dp"
    android:background="@drawable/safe_mode_background"
    android:textColor="@color/safe_mode_text"
    android:text="@string/safeModeTest"
/>

• 资源

frameworks/base/core/res/res/values/string.xml

<string name="safeModeTest">Debug version, cannot be used for external provision</string>

frameworks/base/core/res/res/values-zh-rCN/string.xml

<string name="safeModeTest">当前是调试版本，不可用于对外提供</string>