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我正在做一个谷歌地图应用程序。
我写了一个函数来查找地址。
当我在主要活动中编写代码时，它是工作。
但是当我在另一个活动中写作时。它总是强制关闭应用程序。

出了什么问题，我该如何解决？

这是我的日志：

11-24 08:56:52.659: E/AndroidRuntime(16334): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.zzzzzz/com.example.zzzzzz.Direction}: java.lang.NullPointerException

这是我的主要活动代码查找地址：

        // find address
    final Geocoder geocoder = new Geocoder(MainActivity.this);

    final EditText ed = (EditText) findViewById(R.id.edAddress);
    Button btAddress = (Button) findViewById(R.id.btAddress);
    btAddress.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {

            String Ten = ed.getText().toString();
            try {
                List<Address> l = geocoder.getFromLocationName(Ten, 5);
                if (l != null && l.size() > 0) {
                    int lat = (int) (l.get(0).getLatitude() * 1000000);
                    int lon = (int) (l.get(0).getLongitude() * 1000000);
                    GeoPoint pt = new GeoPoint(lat, lon);

                    p = pt;
                    MapOverlay mar = new MapOverlay();
                    listOfOverlays.add(mar);

                    mv.getController().setZoom(17);
                    mv.getController().setCenter(pt);

                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                Log.v("Loi: ", "Loi 1 cua tui ne");
            }
        }
    });

这是我的功能开始其他活动：

public boolean onOptionsItemSelected(MenuItem item) {
    switch(item.getItemId()) {
    case R.id.about:
        //about
        Intent about = new Intent("com.example.zzzzzz.About");
        startActivity(about);
        break;
    case R.id.setting:
        //setting
        Intent setting = new Intent("com.example.zzzzzz.Setting");
        startActivity(setting);
        break;
    case R.id.direction:
        //direction
        Intent direction = new Intent("com.example.zzzzzz.Direction");
        startActivity(direction);
        break;
    case R.id.MyLocation:
        //mylocation
        //Intent mylocation = new Intent("com.example.zzzzzz.MyLocation");
        //startActivity(mylocation);
        initLocationManagerV2();
        LocationManager locationManager;
        locationManager = (LocationManager)getSystemService (Context.LOCATION_SERVICE);
        Location location = locationManager.getLastKnownLocation (LocationManager.GPS_PROVIDER);
        double lat = location.getLatitude();
        double lng = location.getLongitude();
        GeoPoint find = new GeoPoint((int)(lat*1E6), (int)(lng*1E6));
        mv.getController().animateTo(find);
        mv.invalidate();
        break;
    }

    return false;
}

这是我的指导活动：

public class Direction extends Activity {

MainActivity maintest;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.direction);

    // find address
    final Geocoder geocoder = new Geocoder(maintest);

    final EditText edMylocation = (EditText) findViewById(R.id.edMylocation);
    final EditText edEndpoint = (EditText) findViewById(R.id.edEndpoint);
    Button btDirection = (Button) findViewById(R.id.btDirection);

    btDirection.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {
            String endpoint = edEndpoint.getText().toString();


            try {
                List<Address> l = geocoder.getFromLocationName(endpoint, 5);
                if (l != null && l.size() > 0) {
                    int lat = (int) (l.get(0).getLatitude() * 1000000);
                    int lon = (int) (l.get(0).getLongitude() * 1000000);
                    GeoPoint pt = new GeoPoint(lat, lon);

                    //p = pt;
                    //MapOverlay mar = new MapOverlay();
                    //listOfOverlays.add(mar);

                    maintest.mv.getController().setZoom(17);
                    //maintest.mv.getController().setCenter(pt);

                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                Log.v("Loi: ", "Loi 1 cua tui ne");
            }

        }
    });

}

}

////////////////////////////////这是我做的功能（AndylandDev）：

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == 1 && resultCode == RESULT_OK) {

        String endpoint = data.getStringExtra("endpoint");
        final Geocoder geocoder = new Geocoder(MainActivity.this);
        try {
            List<Address> l = geocoder.getFromLocationName(endpoint, 5);
            if (l != null && l.size() > 0) {
                int lat = (int) (l.get(0).getLatitude() * 1000000);
                int lon = (int) (l.get(0).getLongitude() * 1000000);
                GeoPoint pt = new GeoPoint(lat, lon);

                p = pt;
                //MapOverlay mar = new MapOverlay();
                //listOfOverlays.add(mar);

                mv.getController().setZoom(17);
                mv.getController().setCenter(pt);

            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            Log.v("Loi: ", "Loi 1 cua tui ne");
        }
    }
}
4

1 回答 1

1

所以

new Geocoder(maintest);

可能会抛出 NullPointerException 因为您的 maintest 变量为空。一般来说，活动不应该像这样直接访问彼此。这将是正确的方法：

当您开始方向活动时：

case R.id.direction:
    //direction
    Intent direction = new Intent("com.example.zzzzzz.Direction");
    startActivityForResult(direction, 1);
    break;

在Direction Activity的onCreate()中

...

btDirection.setOnClickListener(new OnClickListener() {

    public void onClick(View v) {
        Intent intent = new Intent();
        intent.putExtra("endpoint", edEndpoint.getText().toString());
        setResult(RESULT_OK, intent);
        finish();
});

...

然后将此方法添加到 MainActivity

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

if (requestCode == 1 && resultCode == RESULT_OK) {

    String endpoint = data.getStringExtra("endpoint");
    //do whatever with it
}
于 2012-11-24T04:26:11.217 回答