1.先在

MainActivity建一个方法

public void sendMessage(View view) {
    // Do something in response to button
    System.out.println("点击文字");
}

2.在下图添加点击事件

3.连机，点击文字后，调用方法。后台打印文字

 主类：Case23.java

package com.example.myapplication;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import androidx.core.content.FileProvider;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;

public class Case23 extends AppCompatActivity {
    public static final int TAKE_PHOTO = 1;//声明一个请求码，用于识别返回的结果
    private ImageView picture;
    private Uri imageUri;
    private final String filePath = Environment.getExternalStorageDirectory() + File.separator + "output_image.jpg";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_case23);

        //点击事件进行拍照
        Button takephoto = findViewById(R.id.take_photo);
        picture = findViewById(R.id.picture);
        takephoto.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                //动态请求相机权限
                requestPermission();  //在其中若用户给予权限则请求相机拍照
            }
        });
        //设置默认图片
        setDefualtImage();
    }

    //动态请求权限
    private void requestPermission() {

        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            //请求权限
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.CAMERA}, 1);
        } else {
            //调用
            requestCamera();
        }
    }


    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (grantResults != null && grantResults.length != 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            switch (requestCode) {
                case 1: {
                    requestCamera();
                }
                break;
            }
        }
    }


    private void requestCamera() {
        File outputImage = new File(filePath);
                /*
                创建一个File文件对象，用于存放摄像头拍下的图片，我们把这个图片命名为output_image.jpg
                并把它存放在应用关联缓存目录下，调用getExternalCacheDir()可以得到这个目录，为什么要
                用关联缓存目录呢？由于android6.0开始，读写sd卡列为了危险权限，使用的时候必须要有权限，
                应用关联目录则可以跳过这一步
                 */
        try//判断图片是否存在，存在则删除在创建，不存在则直接创建
        {
            if (!outputImage.getParentFile().exists()) {
                outputImage.getParentFile().mkdirs();
            }
            if (outputImage.exists()) {
                outputImage.delete();
            }

            outputImage.createNewFile();

            if (Build.VERSION.SDK_INT >= 24) {
                imageUri = FileProvider.getUriForFile(this,
                        "com.example.mydemo.fileprovider", outputImage);
            } else {
                imageUri = Uri.fromFile(outputImage);
            }
            //使用隐示的Intent，系统会找到与它对应的活动，即调用摄像头，并把它存储
            Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
            intent.putExtra(MediaStore.EXTRA_OUTPUT, imageUri);
            startActivityForResult(intent, TAKE_PHOTO);
            //调用会返回结果的开启方式，返回成功的话，则把它显示出来
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    //处理返回结果的函数，下面是隐示Intent的返回结果的处理方式，具体见以前我所发的intent讲解
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode) {
            case TAKE_PHOTO:
                if (resultCode == RESULT_OK) {
                    try {
                        Bitmap bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(imageUri));
                        picture.setImageBitmap(bitmap);
                        //将图片解析成Bitmap对象，并把它显现出来
                    } catch (FileNotFoundException e) {
                        e.printStackTrace();
                    }
                }
                break;
            default:
                break;
        }
    }

    //设置保存拍照图片——>再次关闭app重新打开显示为上次拍照照片
    private void setDefualtImage() {
        File outputImage = new File(filePath);
        if (!outputImage.exists()) {
            return;
        }
        picture.setImageBitmap(BitmapFactory.decodeFile(filePath));
    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.myapplication">
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:requestLegacyExternalStorage="true"
        android:theme="@style/Theme.MyApplication">
        <provider
            android:name="androidx.core.content.FileProvider"
            android:authorities="com.example.mydemo.fileprovider"
            android:exported="false"
            android:grantUriPermissions="true"
            tools:ignore="WrongManifestParent">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/file_paths" />
        </provider>
        <activity
            android:name=".Case23"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

布局项目：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.myapplication.Case23"
    tools:ignore="MissingConstraints">

    <Button
        android:id="@+id/take_photo"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="调用摄像头拍照"
        android:textSize="20sp" />

    <ImageView
        android:id="@+id/picture"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>