[移动开发]Android 权限动态请求

在Android M版本以后，权限就没办法Manifest声明就万事了，还需要动态请求。

网上已经有不少例子，不过这里还是做一个简单的activity，把动态请求的方法，完整的实现一下，基本可以复制粘贴使用。

首先，manifest还是声明一下，兼容老版本。

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

然后，写一个WelcomeActivity，把权限拿到，再进入下一步。

import static android.Manifest.permission.READ_EXTERNAL_STORAGE;
import static android.Manifest.permission.WRITE_EXTERNAL_STORAGE;

import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import com.google.android.material.snackbar.Snackbar;

public class WelcomeActivity extends AppCompatActivity implements View.OnClickListener {
    private static final int PERMISSION_REQUEST_CODE = 200;
    private View view;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_welcome);
        Button check_permission = (Button) findViewById(R.id.check_permission);
        Button request_permission = (Button) findViewById(R.id.request_permission);
        check_permission.setOnClickListener(this);
        request_permission.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        view = v;
        int id = v.getId();
        switch (id) {
            case R.id.check_permission:
                if (checkPermission()) {
                    Snackbar.make(view, "Permission already granted.", Snackbar.LENGTH_LONG).show();
                } else {
                    Snackbar.make(view, "Please request permission.", Snackbar.LENGTH_LONG).show();
                }
                break;
            case R.id.request_permission:
                if (!checkPermission()) {
                    requestPermission();
                } else {
                    Snackbar.make(view, "Permission already granted.", Snackbar.LENGTH_LONG).show();
                    goNext();
                }
                break;
        }
    }

    private boolean checkPermission() {
        int result = ContextCompat.checkSelfPermission(getApplicationContext(), READ_EXTERNAL_STORAGE);
        int result1 = ContextCompat.checkSelfPermission(getApplicationContext(), WRITE_EXTERNAL_STORAGE);

        return result == PackageManager.PERMISSION_GRANTED && result1 == PackageManager.PERMISSION_GRANTED;
    }

    private void requestPermission() {
        ActivityCompat.requestPermissions(this, new String[]{READ_EXTERNAL_STORAGE, WRITE_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
    }

    private void goNext() {
        Intent intent = new Intent(this, MainActivity.class);
        startActivity(intent);
        finish();
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        switch (requestCode) {
            case PERMISSION_REQUEST_CODE:
                if (grantResults.length > 0) {
                    boolean readAccepted = grantResults[0] == PackageManager.PERMISSION_GRANTED;
                    boolean writeAccepted = grantResults[1] == PackageManager.PERMISSION_GRANTED;

                    if (readAccepted && writeAccepted) {
                        Snackbar.make(view, "Permission Granted", Snackbar.LENGTH_LONG).show();
                        goNext();
                    } else {
                        Snackbar.make(view, "Permission Denied", Snackbar.LENGTH_LONG).show();
                        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                            if (shouldShowRequestPermissionRationale(WRITE_EXTERNAL_STORAGE)) {
                                showMessageOKCancel("You need to allow access to both the permissions",
                                        new DialogInterface.OnClickListener() {
                                            @Override
                                            public void onClick(DialogInterface dialog, int which) {
                                                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                                                    requestPermissions(new String[]{READ_EXTERNAL_STORAGE, WRITE_EXTERNAL_STORAGE},
                                                            PERMISSION_REQUEST_CODE);
                                                }
                                            }
                                        });
                                return;
                            }
                        }
                    }
                }
                break;
        }
    }

    private void showMessageOKCancel(String message, DialogInterface.OnClickListener okListener) {
        new AlertDialog.Builder(this)
                .setMessage(message)
                .setPositiveButton("OK", okListener)
                .setNegativeButton("Cancel", null)
                .create()
                .show();
    }
}

上面的例子，提到了存储权限，这里就顺带说一个注意事项。
如果你的gradle的targetSDK > 29，则需要在manifest的application标签，加
android:requestLegacyExternalStorage = "true"
原因是，从Android Q开始，出于数据隐私问题，Android 希望禁止应用程序操作非沙箱内的数据（app私有存储目录，例如QQ的外部存储目录，/sdcard/Android/data/com.tencent.qq/，为沙箱数据，可以随意读写）。 但是为了过度，Android提供了requestLegacyExternalStorage机制，来帮助应用使用原来的机制继续读写存储卡。