2022-11-3学习内容

标签：11 chapter06 java 学习 2022 import path android public

1.在存储卡上读写图片文件

1.1activity_image_write.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/btn_save"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="保存"/>

    <Button
        android:id="@+id/btn_read"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="读取"/>

    <ImageView
        android:id="@+id/iv_content"
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:scaleType="fitCenter" />

</LinearLayout>

1.2ImageWriteActivity.java

package com.example.chapter06;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;

import com.example.chapter06.util.FileUtil;
import com.example.chapter06.util.ToastUtil;

import java.io.File;

public class ImageWriteActivity extends AppCompatActivity implements View.OnClickListener{

    private String path;
    private ImageView iv_content;

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

        iv_content = findViewById(R.id.iv_content);

        findViewById(R.id.btn_save).setOnClickListener(this);
        findViewById(R.id.btn_read).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch(v.getId()) {
            case R.id.btn_save:
                String fileName = System.currentTimeMillis() + ".jpeg";
                // 内部存储私有空间
                path = getFilesDir().toString() + File.separatorChar + fileName;
                Log.d("ning", path);
                // 从指定的资源文件中获取位图对象
                Bitmap b1 = BitmapFactory.decodeResource(getResources(), R.drawable.ting1);
                // 把位图对象保存为图片文件
                FileUtil.saveImage(path, b1);
                ToastUtil.show(this, "保存成功");
                break;

            case R.id.btn_read:
//                Bitmap b2 = FileUtil.openImage(path);
//                iv_content.setImageBitmap(b2);

//                Bitmap b2 = BitmapFactory.decodeFile(path);
//                iv_content.setImageBitmap(b2);

                // 直接调用setImageURI方法，设置图像视图的路径对象
                iv_content.setImageURI(Uri.parse(path));
                break;
        }
    }
}

1.3FileUtil.java

package com.example.chapter06.util;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class FileUtil {

    // 把字符串保存到指定路径的文本文件
    public static void saveText(String path, String txt) {
        BufferedWriter os = null;
        try {
            os = new BufferedWriter(new FileWriter(path));
            os.write(txt);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (os != null) {
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    // 从指定路径的文本文件中公读取内容字符串
    public static String openText(String path) {
        BufferedReader is = null;
        StringBuilder sb = new StringBuilder();
        try {
            is = new BufferedReader(new FileReader(path));
            String line = null;
            while((line = is.readLine()) != null) {
                sb.append(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return sb.toString();
    }

    // 把位图数据保存到指定路径的图片文件
    public static void saveImage(String path, Bitmap bitmap) {
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(path);
            // 把位图数据压缩到文件输出流中
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    // 从指定路径的图片文件中读取位图数据
    public static Bitmap openImage(String path) {
        Bitmap bitmap = null;
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(path);
            bitmap = BitmapFactory.decodeStream(fis);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return bitmap;
    }
}

1.4效果：

点击“保存”：

 

 控制台输出：

D/ning: /data/user/0/com.example.chapter06/files/1667433855229.jpeg

验证：

 

 

 

 点击“读取”：

 

 “读取”按钮点击事件里，注释掉的两种方法，与上图效果相同，已验证，就不截图了。

2.Application生命周期

2.1MyApplication.java

package com.example.chapter06;

import android.app.Application;
import android.content.res.Configuration;
import android.util.Log;

import androidx.annotation.NonNull;

public class MyApplication extends Application {

    // 在APP启动时调用
    @Override
    public void onCreate() {
        super.onCreate();
        Log.d("ning", "MyApplication onCreate");
    }

    // 在APP终止时调用
    @Override
    public void onTerminate() {
        super.onTerminate();
        Log.d("ning", "onTerminate");
    }

    // 在配置改变时调用，例如从竖屏变为横屏
    @Override
    public void onConfigurationChanged(@NonNull Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        Log.d("ning", "onConfigurationChanged");
    }
}

2.2MainActivity.java

package com.example.chapter06;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d("ning", "MainActivity onCreate");
    }
}

2.3AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.chapter06">

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

    <application
        android:name=".MyApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:requestLegacyExternalStorage="true"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.MyApplication">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

2.4效果：

启动APP后控制台输出：

2022-11-03 19:05:51.491 3361-3361/com.example.chapter06 D/ning: MyApplication onCreate
2022-11-03 19:05:52.786 3361-3361/com.example.chapter06 D/ning: MainActivity onCreate

旋转手机后，控制台输出：

2022-11-03 19:09:33.808 3361-3361/com.example.chapter06 D/ning: onConfigurationChanged
2022-11-03 19:09:33.999 3361-3361/com.example.chapter06 D/ning: onConfigurationChanged
2022-11-03 19:09:34.475 3361-3361/com.example.chapter06 D/ning: MainActivity onCreate

屏幕：

 

标签：11,chapter06,java,学习,2022,import,path,android,public
From： https://www.cnblogs.com/pingfanliliang/p/16853150.html