Android WebView调用相机权限适配异常求助（Android 6升级后）

Hey there, let's dig into this issue and figure out what's going wrong, plus how to fix it!

Why this is happening on Android 6+ #

Android 6.0 (API 23) introduced runtime permission requests for "dangerous" permissions like camera and storage—something older Android versions handled automatically at install time. When you swapped the native <input> click behavior for a Java callback, you took on the responsibility of managing these permissions properly, and it sounds like that flow has a gap right now.

Common missteps that cause this issue:

• You're not fully completing the permission request flow (e.g., asking for permissions but not waiting for the user's response before trying to launch the camera/file picker)
• You're requesting the wrong permissions, or forgetting to declare them in your manifest
• After the user grants permissions, you're not re-triggering the original <input> click that launches the system's picker/camera
• Your WebView's WebChromeClient isn't properly handling the file chooser callback (required for Android 5+ WebView file selection)

Step-by-step fixes #

1. Declare required permissions in your AndroidManifest.xml

First, make sure you've listed the permissions your app needs:

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<!-- For Android 10+, add this if needed -->
<uses-permission android:name="android.permission.ACCESS_MEDIA_LOCATION" />

2. Fix the permission request flow in your Java code

Instead of replacing the <input> entirely, use your Java callback to handle permissions first, then trigger the original <input> click once permissions are granted. Here's a concrete example:

// Define a request code for permission checks
private static final int REQUEST_IMAGE_PERMISSIONS = 1001;
private WebView mWebView;

// This is the method your HTML click event calls via @JavascriptInterface
@JavascriptInterface
public void triggerImagePicker() {
    // Check if we already have the required permissions
    boolean hasCameraPerm = ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED;
    boolean hasStoragePerm = ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED;

    if (hasCameraPerm && hasStoragePerm) {
        // Permissions are good—trigger the hidden input's click
        mWebView.loadUrl("javascript:document.getElementById('InputImgFileDialog').click()");
    } else {
        // Request missing permissions
        String[] permissions = {Manifest.permission.CAMERA, Manifest.permission.READ_EXTERNAL_STORAGE};
        ActivityCompat.requestPermissions(this, permissions, REQUEST_IMAGE_PERMISSIONS);
    }
}

// Handle the permission request result
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if (requestCode == REQUEST_IMAGE_PERMISSIONS) {
        boolean allPermissionsGranted = true;
        for (int result : grantResults) {
            if (result != PackageManager.PERMISSION_GRANTED) {
                allPermissionsGranted = false;
                break;
            }
        }

        if (allPermissionsGranted) {
            // User said yes—launch the picker
            mWebView.loadUrl("javascript:document.getElementById('InputImgFileDialog').click()");
        } else {
            // User denied permissions—show a helpful message
            Toast.makeText(this, "We need camera and storage permissions to select photos", Toast.LENGTH_SHORT).show();
        }
    }
}

3. Ensure your WebChromeClient handles file selection

Android 5+ WebViews require you to implement onShowFileChooser in your WebChromeClient to properly handle file picker triggers. Add this to your WebView setup:

mWebView.setWebChromeClient(new WebChromeClient() {
    @Override
    public boolean onShowFileChooser(WebView webView, ValueCallback<Uri[]> filePathCallback, FileChooserParams fileChooserParams) {
        // If you're relying on the native <input> behavior, you can use the default implementation
        // Or customize it here if you need more control over the picker
        return super.onShowFileChooser(webView, filePathCallback, fileChooserParams);
    }
});

4. Test edge cases

• Make sure you handle the scenario where the user denies permissions and checks "Don't ask again"—you'll need to redirect them to app settings to enable permissions manually.
• Verify that the <input> tag's capture="camera" attribute still works as expected once permissions are granted (it should launch the camera directly if the device supports it).

Quick recap #

The core issue is that Android 6+ requires explicit runtime permission checks, which the native <input> handled automatically in older versions. By adding the permission request flow in your Java callback and re-triggering the original <input> click after approval, you'll restore the expected behavior while complying with Android's security rules.

内容的提问来源于stack exchange，提问作者Steve Brooker