Electronic device and controlling method thereof

An electronic device, comprising:

• a screen;
• a distance sensor, configured to transmit an acknowledgement signal, and receive a feedback signal responding to the acknowledgement signal;
• a memory, configured to store at least one program instruction, a first threshold value, a second threshold value, and a predetermined value, wherein the first threshold value is less than the second threshold value;
• and
• a processor, electrically connected to the distance sensor and the memory, and loading the at least one program instruction to perform the following steps:
• receiving the feedback signal from the distance sensor;
• determining a signal strength value of the feedback signal;
• obtaining the first threshold value and the second threshold value from the memory;
• and
• comparing the signal strength value with the first threshold value and the second threshold value;
• wherein the processor controls the screen to operate in a first mode when the signal strength value is greater than the first threshold and the second threshold value;
• and the processor compares the signal strength value with the predetermined value to determine whether any foreign matter is adhered on the screen or the distance sensor when the signal strength value is greater than the first threshold value but not greater than the second threshold value;
• and the processor adjusts the first threshold value to be the signal strength value to control the screen to operate in a second mode when the signal strength value is greater than the predetermined value, wherein the second mode is different from the first mode.