我无法更新进度条

Question

我正在尝试使用AsyncTasks 功能制作一个简单的应用程序。问题出在onProgressUpdate()。每当尝试运行我的应用程序时，我都会收到 java.lang.NullPointerException。我已经检查了LogCat。但是我找不到错误的来源。

这是第 94 行。Eclipse 说它为空。

progress_bar.setProgress(values[0]);

这是输出

 05-19 05:43:07.895: E/AndroidRuntime(2038): FATAL EXCEPTION: main
    05-19 05:43:07.895: E/AndroidRuntime(2038): Process: com.example.ssdsd, PID: 2038
    05-19 05:43:07.895: E/AndroidRuntime(2038): java.lang.NullPointerException
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at com.example.ssdsd.MainActivity$MyAsyn.onProgressUpdate(MainActivity.java:94)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at com.example.ssdsd.MainActivity$MyAsyn.onProgressUpdate(MainActivity.java:1)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:648)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at android.os.Handler.dispatchMessage(Handler.java:102)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at android.os.Looper.loop(Looper.java:137)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at android.app.ActivityThread.main(ActivityThread.java:4998)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at java.lang.reflect.Method.invokeNative(Native Method)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at java.lang.reflect.Method.invoke(Method.java:515)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
    05-19 05:43:07.895: E/AndroidRuntime(2038):     at dalvik.system.NativeStart.main(Native Method)

这是我的代码

public class MainActivity extends Activity {
    static final int SLEEP_TIME=(15*1000)/100;
    Dialog dialog;
    ProgressBar progress_bar;
    TextView tvper;
    Button btnstart;
    MyAsyn asynClass;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnstart=(Button)findViewById(R.id.start);
        btnstart.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                asynClass=new MyAsyn();
                asynClass.execute();

            }
        });
    }



    public class MyAsyn extends AsyncTask<Void, Integer, Void>{


        @Override
        protected void onPreExecute() {
            // TODO Auto-generated method stub
            super.onPreExecute();
            dialog=new Dialog(MainActivity.this);

            dialog.setContentView(R.layout.progress_view);
            progress_bar=(ProgressBar)findViewById(R.id.pgbar);
            tvper=(TextView)findViewById(R.id.tvper);


            dialog.show();

        }
        @Override
        protected Void doInBackground(Void... params) {

            for (int i = 0; i < 100; i++) {
                if(isCancelled()){

                    break;
                }
                else {
                    try {
                        publishProgress(i);
                        Thread.sleep(SLEEP_TIME);
                    } catch (Exception e) {
                        // TODO: handle exception
                    }
                }
            }       


            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);

            dialog.dismiss();
        }



        @Override
        protected void onProgressUpdate(Integer... values) {
            // TODO Auto-generated method stub
            super.onProgressUpdate(values);
            try {
                progress_bar.setProgress(values[0]);

            } catch (Exception e) {
                e.printStackTrace();
            }
        //  tvper.setText("Loading "+values[0]+"%");

        }

Answer 1

您的 progress_bar 为空。使用前需要使用 findViewById(R.id.xyz) 找到它。