android开发app怎么实现上传图片

在 Android 开发中，实现图片的上传可以通过以下步骤来完成：

一、获取权限

首先需要获取读取和写入存储空间的权限，以涵盖图片选择和保存。

Manifest.xml:

```xml

```

二、UI设计

通过布局文件制作上传图片的界面。该界面通常包括一个“选择图片”的按钮和一个显示所选图像的 ImageView。

activity_main.xml:

```xml

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:orientation="vertical" >

android:id="@+id/btn_select_image"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="选择图片" />

android:id="@+id/img_selected"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginTop="20dp"

android:src="@drawable/placeholder" />

```

三、选择图片

通过 startActivityForResult 和 Intent 调用图库或者拍照程序来实现图片选择的操作。在用户选择或拍摄照片后，处理结果。

MainActivity.java:

```java

public class MainActivity extends AppCompatActivity {

private static final int REQUEST_PICK_IMAGE = 101;

private ImageView imgSelected;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

Button btnSelectImage = (Button) findViewById(R.id.btn_select_image);

imgSelected = (ImageView) findViewById(R.id.img_selected);

btnSelectImage.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

Intent intent = new Intent(Intent.ACTION_GET_CONTENT);

intent.setType("image/*");

startActivityForResult(intent, REQUEST_PICK_IMAGE);

}

});

}

@Override

protected void onActivityResult(int requestCode, int resultCode, Intent data) {

super.onActivityResult(requestCode, resultCode, data);

if (requestCode == REQUEST_PICK_IMAGE && resultCode == RESULT_OK && data != null) {

Uri uri = data.getData();

try {

Bitmap bitmap = MediaStore.Images.Media.getBitmap(getContentResolver(), uri);

imgSelected.setImageBitmap(bitmap);

} catch (IOException e) {

e.printStackTrace();

}

}

}

}

```

四、上传图片

在图像已被选中后，发起网络请求将其上传到服务器。通常使用 OkHttp 库来实现 Post 请求。

build.gradle:

```gradle

dependencies {

implementation 'com.squareup.okhttp3:okhttp:3.12.3'

}

```

MainActivity.java:

```java

public class MainActivity extends AppCompatActivity {

private static final int REQUEST_PICK_IMAGE = 101;

private ImageView imgSelected;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

Button btnSelectImage = (Button) findViewById(R.id.btn_select_image);

imgSelected = (ImageView) findViewById(R.id.img_selected);

btnSelectImage.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

Intent intent = new Intent(Intent.ACTION_GET_CONTENT);

intent.setType("image/*");

startActivityForResult(intent, REQUEST_PICK_IMAGE);

}

});

}

@Override

protected void onActivityResult(int requestCode, int resultCode, Intent data) {

super.onActivityResult(requestCode, resultCode, data);

if (requestCode == REQUEST_PICK_IMAGE && resultCode == RESULT_OK && data != null) {

Uri uri = data.getData();

try {

Bitmap bitmap = MediaStore.Images.Media.getBitmap(getContentResolver(), uri);

imgSelected.setImageBitmap(bitmap);

String url = "http://yourserver.com/upload";

RequestBody requestBody = new MultipartBody.Builder()

.setType(MultipartBody.FORM)

.addFormDataPart("image", "image", RequestBody.create(MediaType.parse("image/*"), new File(getPathFromUri(uri))))

.build();

Request request = new Request.Builder()

.url(url)

.post(requestBody)

.build();

OkHttpClient client = new OkHttpClient();

client.newCall(request).enqueue(new Callback() {

@Override

public void onFailure(Call call, IOException e) {

Log.e("Upload", "Upload image error", e);

}

@Override

public void onResponse(Call call, Response response) throws IOException {

String result = response.body().string();

Log.i("Upload", "Upload image succeed: " + result);

}

});

} catch (IOException e) {

e.printStackTrace();

}

}

}

private String getPathFromUri(Uri uri) {

Cursor cursor = getContentResolver().query(uri, null, null, null, null);

String path = "";

if (cursor != null) {

cursor.moveToFirst();

String[] columns = cursor.getColumnNames();

for (String column : columns) {

Log.d("getColumnNames", column);

}

int columnIndex = cursor.getColumnIndex(MediaStore.Images.Media.DATA);

if (columnIndex != -1) {

path = cursor.getString(columnIndex);

} else {

String id = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media._ID));

path = MediaStore.Images.Media.EXTERNAL_CONTENT_URI.toString() + "/" + id;

}

cursor.close();

}

return path;

}

}

```

以上就是 Android 开发中上传图片的实现原理或者详细介绍，通过这些简单的步骤，就可以很容易地实现图片的上传功能。