Question

所以我检查了R.id.button（我的按钮ID的名称），以确保它是好的，但是每当我尝试运行点击按钮时，它就会吓坏了，Log Cat告诉我我已经得到一个空指针异常。任何帮助将不胜感激，代码如下。

    public class RSSReaderActivity extends Activity {
        RSSParser RSStext;
        public EditText url;
        Button feedButton;
        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);
            url = (EditText) findViewById(R.id.url_text);
            feedButton = (Button) findViewById(R.id.button);
            setContentView(R.layout.main);
        }

        public boolean onCreateOptionsMenu (Menu menu){
            MenuInflater inflater = getMenuInflater();
            inflater.inflate(R.menu.menu, menu);
            return true;//true makes visible
        }

        public boolean onOptionsItemSelected(MenuItem item){
            switch(item.getItemId()){
                case R.id.exit: this.finish();
            }
            return true;//true makes visible
        }

        public void parser(View view){//test code
            if(url.equals(null)){ //This is the line where my error is thrown according to log cat
                Toast toast = Toast.makeText(getApplicationContext(), "No URL entered!", 5);
                toast.show();
            }
            else{
                String temp = url.toString();
                RSStext = new RSSParser(temp);
            }
        }
    }

我的主要类的XML：

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center|top"
        android:orientation="vertical" xmlns:android="http://schemas.android.com/apk/res/android">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:text="@string/hello" />

        <EditText
            android:id="@+id/url_text"
            android:layout_width="fill_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:clickable="true"
            android:inputType="textUri"
            android:text="@string/default_url" />

        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:onClick="parser"
            android:text="@string/feed_button" />

    </LinearLayout>

Answer 1

您必须在获取EditText之前设置contentview

@Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        url = (EditText) findViewById(R.id.url_text);
        feedButton = (Button) findViewById(R.id.button);

    }

为按钮抛出空指针异常

1 个答案: