Question

我正在尝试将值从1个活动传递到另一个，该值来自intent方法..但是在将值传递给第二个intent时我得到一个空指针异常..所以我做错了什么？？在main方法中（url在那里有一个值）

public void passStringToIntent(String url) {

        final Intent intent = new Intent(Question_Point_Main.this, AccessPdf.class);
        intent.putExtra("URL", url);
        startActivity(intent);
      }

第二种方法中的

（访问值）

Intent intent = getIntent();
String url = intent.getStringExtra("URL");

我的日志猫如下

E/AndroidRuntime(1892): FATAL EXCEPTION: main
E/AndroidRuntime(1892): Process: com.example.testqstn, PID: 1892
E/AndroidRuntime(1892): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.testqstn/com.questionpoint.pdf.AccessPdf}: java.lang.NullPointerException
E/AndroidRuntime(1892):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
E/AndroidRuntime(1892):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
E/AndroidRuntime(1892):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
E/AndroidRuntime(1892):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
E/AndroidRuntime(1892):     at android.os.Handler.dispatchMessage(Handler.java:102)
E/AndroidRuntime(1892):     at android.os.Looper.loop(Looper.java:136)
E/AndroidRuntime(1892):     at android.app.ActivityThread.main(ActivityThread.java:5017)
E/AndroidRuntime(1892):     at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(1892):     at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime(1892):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
E/AndroidRuntime(1892):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
E/AndroidRuntime(1892):     at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(1892): Caused by: java.lang.NullPointerException
E/AndroidRuntime(1892):     at com.questionpoint.pdf.AccessPdf.<init>(AccessPdf.java:22)
E/AndroidRuntime(1892):     at java.lang.Class.newInstanceImpl(Native Method)
E/AndroidRuntime(1892):     at java.lang.Class.newInstance(Class.java:1208)
E/AndroidRuntime(1892):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
E/AndroidRuntime(1892):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
E/AndroidRuntime(1892):     ... 11 more

访问pdf .java / 2nd活动

    public class AccessPdf  extends Activity {

    Intent intent = getIntent();
    String url = intent.getStringExtra("URL"); <--- line 22
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        AssetManager assetManager = getAssets();

        InputStream in = null;
        OutputStream out = null;
        File file = new File(getFilesDir(), url);
        try
        {
            in = assetManager.open(url);
            out = openFileOutput(file.getName(), Context.MODE_WORLD_READABLE);

            copyFile(in, out);
            in.close();
            in = null;
            out.flush();
            out.close();
            out = null;
        } catch (Exception e)
        {
            Log.e("tag", e.getMessage());
        }

        Intent intent = new Intent(this, Pdf.class);
        intent.putExtra(PdfViewerActivity.EXTRA_PDFFILENAME, getFilesDir()+"/"+url);
        startActivity(intent);
        /* 
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(
                Uri.parse("file://" + getFilesDir() + "/ABC.pdf"),
                "application/pdf");

        startActivity(intent);*/
    }

    private void copyFile(InputStream in, OutputStream out) throws IOException
    {
        byte[] buffer = new byte[1024];
        int read;
        while ((read = in.read(buffer)) != -1)
        {
            out.write(buffer, 0, read);
        }
    }

Answer 1

此

Intent intent = getIntent();
String url = intent.getStringExtra("URL");<--- line 22

应该进入onCreate。

 @Override
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    String url = getIntent().getStringExtra("URL");
    ...// rest of the code

无法使用java.lang.nullpointerexception实例化活动componentinfo

1 个答案: