安卓不能使用前置摄像头

plus.camera.getCamera(); 设置了参数为2 ，还是不能使用前置摄像头

var cmr = plus.camera.getCamera(2);
var res = cmr.supportedImageResolutions[0];
var fmt = cmr.supportedImageFormats[0];
console.log("Resolution: "+res+", Format: "+fmt);
cmr.captureImage( function( path ){
console.log(res);

                    },  
                    function( error ) {  
                        alert( "Capture image failed: " + error.message );  
                    },  
                );