android - startActivityForResult中的空指针异常

我正在尝试从HTML5和JavaScript调用相机。我的代码如下。但是我得到了空指针异常。

主要活动：

 public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
            WebView webview=(WebView)findViewById(R.id.webkitWebView1);
            WebSettings settings = webview.getSettings();
            settings.setJavaScriptEnabled(true);
            //load html5 page
            webview.loadUrl("file:///android_asset/www/html/opencamera.html");

            openCamera=new OpenCamera();
            webview.addJavascriptInterface(openCamera,"camera");

        }

        @Override
        protected void onActivityResult(int requestCode, int resultCode, Intent data) {
            if (requestCode== 0 && resultCode == Activity.RESULT_OK){
                System.out.println("Done");
            }
        }

拍照电话：

public class OpenCamera extends Activity {

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    public void startCameraActivity(){
        Intent intent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE );
        startActivityForResult(intent,0);
    }

}

html页面：

 <!DOCTYPE HTML>
    <html>
    <head>
    <script type="text/javascript">
    function openCamera(){
        //alert("cameras");
        camera.startCameraActivity();
    }
    </script>


    <title>Welcome</title>
    </head>
    <body>
    Hello World!!!
    <br/>
    <button type="button" onclick="openCamera()">Capture Image</button>
    </body>
    </html>

清单中的权限：

<uses-feature android:name="android.hardware.camera" />
    <uses-permission android:name="android.permission.CAMERA" />
    <uses-feature android:name="android.hardware.camera.autofocus" />
    <uses-permission android:name="android.permission.INTERNET" />

Logcat：

11-16 08:56:07.133: ERROR/AndroidRuntime(539): java.lang.NullPointerException
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at android.app.Activity.startActivityForResult(Activity.java:2817)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at com.test.camera.OpenCamera.startCameraActivity(OpenCamera.java:17)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at android.webkit.WebViewCore.nativeTouchUp(Native Method)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at android.webkit.WebViewCore.nativeTouchUp(Native Method)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at android.webkit.WebViewCore.access$3300(WebViewCore.java:52)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at android.webkit.WebViewCore$EventHub$1.handleMessage(WebViewCore.java:1150)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at android.os.Looper.loop(Looper.java:123)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at android.webkit.WebViewCore$WebCoreThread.run(WebViewCore.java:621)
11-16 08:56:07.133: ERROR/AndroidRuntime(539):     at java.lang.Thread.run(Thread.java:1096)

最佳答案

您从尚未启动的Camera Activity活动（根据android启动OpenCamera的方式）开始Activity，所以OpenCamera活动的上下文为null，这就是为什么Context为null的原因当时导致NullPointerException。

解决方法：

将上下文传递给功能startCameraActivity()为

public void startCameraActivity(Context con){
        Intent intent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE );
        con.startActivityForResult(intent,0);
}

将上下文传递给WebView

webview.addJavascriptInterface(this,"context");

并在您的脚本中

<script type="text/javascript">
    function openCamera(){
        camera.startCameraActivity(context);
    }
</script>

OpenCamera不必是Activity

关于android - startActivityForResult中的空指针异常，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/8146539/