手机dp和px的转换
1dp 0.75px ----> 320*240
1dp 1px ----->480*320
1dp 1.5px ----->800*480 4英寸屏
1dp 2px ----->1280*720 5英寸屏左右
1dp 3px ----> 1920*1280 5英寸屏左右
zengsf 懒惰、高效、实用
1dp 0.75px ----> 320*240
1dp 1px ----->480*320
1dp 1.5px ----->800*480 4英寸屏
1dp 2px ----->1280*720 5英寸屏左右
1dp 3px ----> 1920*1280 5英寸屏左右