Android调用系统相机拍照，从图库中选择照片，调用系统摄像机录像

最近在Android Studio上折腾代码，昨天编译器又很不给面子的报错了:

Error type 3Error: Activity class {com.example.myapplication/com.example.myapplication.MainActivity} does not exist.

程序都安装不起来，并不是忘了注册类名，在stackoverflow按照大神们的解决方法试了，没有效果。接下来所有新建的工程都报这个错误，搞得我都怀疑喵生了。。。都准备重装新版本了，1.5版本已出。
今天过来一看，好了，得出结论，重启是万能的：重启了电脑和手机。
先上布局：
这里用了一个ImageView,拍照和图库都用这个显示。显示录像的控件使用的是VideoView。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    >    <Button        android:text="拍照"        android:onClick="takePhoto"        android:layout_width="wrap_content"        android:layout_height="wrap_content" />    <Button        android:text="从手机相册中选择"        android:onClick="choosePhoto"        android:layout_width="wrap_content"        android:layout_height="wrap_content" />    <ImageView        android:id="@+id/iv"        android:layout_width="150dp"        android:layout_height="200dp"        android:layout_gravity="center"        android:background="#ff00ff"        android:scaleType="fitXY"/>    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="录制视频"        android:onClick="takeVideo"/>    <VideoView        android:id="@+id/vv"        android:layout_width="300dp"        android:layout_height="400dp"        android:layout_gravity="center"/></LinearLayout>

import android.content.Context;import android.content.Intent;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.media.MediaPlayer;import android.net.Uri;import android.os.Environment;import android.provider.MediaStore;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import android.view.View;import android.widget.ImageView;import android.widget.MediaController;import android.widget.VideoView;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;public class MainActivity extends AppCompatActivity {    private Context context;    public static final String TAG="MyLog";    private static final  int REQUEST_CAMERA_CAPTURE=1;    private static final  int REQUEST_IMAGE_CAPTURE=2;    private static final  int REQUEST_VIDEO_CAPTURE=3;    private File imagePath,videoPath;    private ImageView mImageView;    private VideoView mVideoView;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        context=this;        mImageView=(ImageView)findViewById(R.id.iv);        mVideoView=(VideoView)findViewById(R.id.vv);    }    public void takePhoto(View view){        takePhoto();    }    public void choosePhoto(View view){        choosePhoto();    }    public void myCamera(View view){myCamera();}    public void takeVideo(View view){        takeVideo();    }    private void takeVideo(){        if(hasSdcard()) {            videoPath = Environment.getExternalStoragePublicDirectory(            Environment.DIRECTORY_MOVIES);            if (!videoPath.exists()) {                videoPath.mkdirs();            }            videoPath = new File(videoPath.getPath() + "/" + "test.mp4");//        直接调用已经存在的录像并播放//        Uri uri=Uri.fromFile(videoPath);//        Intent intent = new Intent(Intent.ACTION_VIEW);//        Log.d(TAG,uri+"");//        intent.setDataAndType(uri, "video/mp4");//        startActivity(intent);            Intent intent = new Intent(MediaStore.ACTION_VIDEO_CAPTURE);            if (intent.resolveActivity(getPackageManager()) != null) {                intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(videoPath));                startActivityForResult(intent, REQUEST_VIDEO_CAPTURE);            }        }    }    private void takePhoto(){        if(hasSdcard()) {Environment.DIRECTORY_PICTURES);            if (!imagePath.exists()) {                imagePath.mkdirs();            }            imagePath = new File(imagePath.getPath() + "/" + "temp.png");            Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);            if (intent.resolveActivity(getPackageManager()) != null) {                intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(imagePath));                startActivityForResult(intent, REQUEST_CAMERA_CAPTURE);            }        }    }    private void choosePhoto(){        Intent intent = new Intent(Intent.ACTION_GET_CONTENT);        intent.setType("image/*");        if (intent.resolveActivity(getPackageManager()) != null) {            startActivityForResult(intent, REQUEST_IMAGE_CAPTURE);        }    }    @Override    protected void onActivityResult(int requestCode, int resultCode, Intent data) {        super.onActivityResult(requestCode, resultCode, data);        if(requestCode==REQUEST_CAMERA_CAPTURE&&resultCode==RESULT_OK){            FileInputStream fis = null;            try {                fis=new FileInputStream(imagePath);                Bitmap bitmap= BitmapFactory.decodeStream(fis);                mImageView.setImageBitmap(bitmap);            } catch (FileNotFoundException e) {                e.printStackTrace();            }finally {                try {                    fis.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }else if(requestCode==REQUEST_IMAGE_CAPTURE&&resultCode==RESULT_OK){            Uri uri=data.getData();            mImageView.setImageURI(uri);        }else if(requestCode==REQUEST_VIDEO_CAPTURE&&resultCode==RESULT_OK){            Uri uri=Uri.fromFile(videoPath);            Log.d(TAG,uri+"");            mVideoView.setVideoURI(uri);            mVideoView.setMediaController(new MediaController(this));            mVideoView.start();            mVideoView.requestFocus();            mVideoView.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {                @Override                public void onCompletion(MediaPlayer mp) {                    Log.d(TAG, "完成");                }            });            mVideoView.setOnErrorListener(new MediaPlayer.OnErrorListener() {                @Override                public boolean onError(MediaPlayer mp, int what, int extra) {                    Log.d(TAG, "播放中出现错误");                    return false;                }            });        }    }private boolean hasSdcard(){        if(Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())){            return true;        }else{            return false;        }    }}

官方说明：
注意在调用startActivityForResult()方法之前，先调用resolveActivity()，这个方法会返回能处理该Intent的第一个Activity（译注：即检查有没有能处理这个Intent的Activity）。执行这个检查非常重要，因为如果在调用startActivityForResult()时，没有应用能处理你的Intent，应用将会崩溃。所以只要返回结果不为null，使用该Intent就是安全的。
最后不要忘了加权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/><uses-permission android:name="android.permission.CAMERA"/>