android - 按返回按钮时出错

Question

在我的 android 应用程序中，当按下后退按钮时，在 logcat 中显示此错误:

09-01 14:07:42.995: E/AndroidRuntime(6279): FATAL EXCEPTION: main
09-01 14:07:42.995: E/AndroidRuntime(6279): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nabege/com.example.nabege.Edit_Collection_Activity}: java.lang.NullPointerException
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.os.Handler.dispatchMessage(Handler.java:99)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.os.Looper.loop(Looper.java:137)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.app.ActivityThread.main(ActivityThread.java:4424)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at java.lang.reflect.Method.invokeNative(Native Method)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at java.lang.reflect.Method.invoke(Method.java:511)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at dalvik.system.NativeStart.main(Native Method)
09-01 14:07:42.995: E/AndroidRuntime(6279): Caused by: java.lang.NullPointerException
09-01 14:07:42.995: E/AndroidRuntime(6279):     at com.example.nabege.Edit_Collection_Activity.onCreate(Edit_Collection_Activity.java:30)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.app.Activity.performCreate(Activity.java:4465)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
09-01 14:07:42.995: E/AndroidRuntime(6279):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
09-01 14:07:42.995: E/AndroidRuntime(6279):     ... 11 more

我的 Activity 代码是这样的:

public class Edit_Collection_Activity extends ActionBarActivity {
    private DB_Nabege_helper nabege_db = new DB_Nabege_helper(this);
    private EditText txt_update_collection;
    private Button btn_update_collection;
    private Button btn_cancel_update_collection;
    private int id_collection;
    private String name_collection;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_edit__collection);

        Bundle extra = getIntent().getExtras();

        id_collection = extra.getInt("id_collection");
        name_collection = extra.getString("name_collection");

        //
        txt_update_collection = (EditText) findViewById(R.id.editText_update_collection);
        txt_update_collection.setText(name_collection);
        // update collection
        btn_update_collection = (Button) findViewById(R.id.btn_update_collection);
        btn_update_collection.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                nabege_db.open();
                nabege_db.update_colletion(id_collection, txt_update_collection.getText().toString());
                nabege_db.close();
                Toast.makeText(getApplicationContext(), "تغییرات با موفقیت ثبت شد.", Toast.LENGTH_SHORT).show();
                //go To pre Activity
                goback();

            }
        });
        //go back
        btn_cancel_update_collection =(Button)findViewById(R.id.btn_update_collection_cancel);
        btn_cancel_update_collection.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                goback();
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.edit__collection_, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
        private void goback() {
    super.finish();
}
}

我在之前的 Activity 中通过以下代码运行 Activity 。在之前的 Activity 中是一个 ListView ，通过单击 ListView 项目显示对话框，然后按下此对话框中的按钮运行以下代码:

 edit_collection.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent goToEditCollectionActivity = new Intent(Collection_List_Activity.this, Edit_Collection_Activity.class);
            startActivity(goToEditCollectionActivity);
            goToEditCollectionActivity.putExtra("id_collection", id_tbl_collection[index_collection]);
            goToEditCollectionActivity.putExtra("name_collection", name_collection_tbl_collection[index_collection]);
            menu_collection_listDialog.cancel();
            startActivity(goToEditCollectionActivity);
        }
    });

请帮忙

Answer 1

你的包是空的，因为你在设置所有这些资源之前调用了 Activity

edit_collection.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
        Intent goToEditCollectionActivity = new Intent(Collection_List_Activity.this, Edit_Collection_Activity.class);
        goToEditCollectionActivity.putExtra("id_collection", id_tbl_collection[index_collection]);
        goToEditCollectionActivity.putExtra("name_collection", name_collection_tbl_collection[index_collection]);
        menu_collection_listDialog.cancel();
        startActivity(goToEditCollectionActivity);
    }
});

此外，每当您必须处理 bundle 时，请始终检查

Bundle extras=getIntent().getExtras();
if(extras!=null){
    //Do something
}else{
    finish();
}