Question

我尝试制作一个Android应用程序，使用asynctask将文本发送到服务器。我成功运行并测试了一个按钮，现在我遇到了五个按钮和五个文本视图的问题。

我的activity_main布局：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/bckgrnd_2"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/button1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="@string/btn1"
        android:onClick="buttonClicked1" />

    <Button
        android:id="@+id/button2"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/button1"
        android:layout_below="@+id/button1"
        android:onClick="buttonClicked2"
        android:text="@string/btn2" />

    <Button
        android:id="@+id/button3"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/button2"
        android:layout_below="@+id/button2"
        android:text="@string/btn3"
        android:onClick="buttonClicked3" />

    <Button
        android:id="@+id/button4"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/button3"
        android:layout_below="@+id/button3"
        android:text="@string/btn4"
        android:onClick="buttonClicked4" />

    <Button
        android:id="@+id/button5"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/button4"
        android:layout_below="@+id/button4"
        android:onClick="buttonClicked5"
        android:text="@string/btn5" />

    <EditText
        android:id="@+id/editText1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/button5"
        android:text="play1" />

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/editText1"
        android:layout_below="@+id/editText2"
        android:text="play2" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/textView1"
        android:layout_below="@+id/editText3"
        android:text="play3" />

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView2"
        android:layout_below="@+id/editText4"
        android:text="play4" />

    <TextView
        android:id="@+id/textView4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView3"
        android:layout_below="@+id/editText5"
        android:text="play5" />

</RelativeLayout>

我的主要活动代码：

public class MainActivity extends Activity {

    private EditText textField;
    private EditText textField1;
    private EditText textField2;
    private EditText textField3;
    private EditText textField4;
    private Button button1;
    private Button button2;
    private Button button3;
    private Button button4;
    private Button button5;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textField =  (EditText) findViewById(R.id.editText1);
        textField1 = (EditText) findViewById(R.id.editText2);
        textField2 = (EditText) findViewById(R.id.editText3);
        textField3 = (EditText) findViewById(R.id.editText4);
        textField4 = (EditText) findViewById(R.id.editText5);

        button1 = (Button) findViewById(R.id.button1);
        button2 = (Button) findViewById(R.id.button2);
        button3 = (Button) findViewById(R.id.button3);
        button4 = (Button) findViewById(R.id.button4);
        button5 = (Button) findViewById(R.id.button5);

        textField.setVisibility(View.GONE);
        textField1.setVisibility(View.GONE);
        textField2.setVisibility(View.GONE);
        textField3.setVisibility(View.GONE);
        textField4.setVisibility(View.GONE);
    }

    public void buttonClicked1(View v){
        Toast.makeText(this, "Song Has Been Successfully Added!", Toast.LENGTH_SHORT).show();

        new asynctask().execute(textField);
    }

    public void buttonClicked2(View v) {
        Toast.makeText(this, "Song Has Been Successfully Added!", Toast.LENGTH_SHORT).show();

        new asynctask().execute(textField1);
    }

    public void buttonClicked3(View v) {
        Toast.makeText(this, "Song Has Been Successfully Added!", Toast.LENGTH_SHORT).show();

        new asynctask().execute(textField2);
    }

    public void buttonClicked4(View v) {
        Toast.makeText(this, "Song Has Been Successfully Added!", Toast.LENGTH_SHORT).show();

        new asynctask().execute(textField3);
    }

    public void buttonClicked5(View v) {
        Toast.makeText(this, "Song Has Been Successfully Added!", Toast.LENGTH_SHORT).show();

        new asynctask().execute(textField4);
    }
}

Asynctask代码：

public class asynctask extends AsyncTask<View, Integer, Socket>
{
    private static final String IP_ADDRESS = "192.168.1.106";
    private static final int DEST_PORT = 7777;

    private EditText mTextField;

    protected Socket doInBackground(View... params)
    {
        if (params.length != 1)
            throw new IllegalArgumentException();

        mTextField = (EditText) params[0];

        Socket client = null;

        try
        {
            client = new Socket(IP_ADDRESS, DEST_PORT);
        }
        catch (UnknownHostException e)
        {
            e.printStackTrace();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        return client;
    }


    protected void onPostExecute(Socket client)
    {
        try
        {
            PrintWriter printwriter;
            String messsage;

            messsage = mTextField.getText().toString();
            mTextField.setText("");

            printwriter = new PrintWriter(client.getOutputStream(), true);
            printwriter.write(messsage);

            printwriter.flush();
            printwriter.close();

            client.close();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }
}

这就是我的logcat所说的：

09-12 01:28:30.914: E/AndroidRuntime(560):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
09-12 01:28:30.914: E/AndroidRuntime(560):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
09-12 01:28:30.914: E/AndroidRuntime(560):     at dalvik.system.NativeStart.main(Native Method)
09-12 01:28:30.914: E/AndroidRuntime(560): Caused by: java.lang.NullPointerException
09-12 01:28:30.914: E/AndroidRuntime(560):     at com.timskie.dancingfountainv1.MainActivity.onCreate(MainActivity.java:46)
09-12 01:28:30.914: E/AndroidRuntime(560):     at android.app.Activity.performCreate(Activity.java:4465)
09-12 01:28:30.914: E/AndroidRuntime(560):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
09-12 01:28:30.914: E/AndroidRuntime(560):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
09-12 01:28:30.914: E/AndroidRuntime(560):     ... 11 more

Answer 1

ID不正确：

textField =  (EditText) findViewById(R.id.editText1); // ???
textField1 = (EditText) findViewById(R.id.textView1); // Here is text, but above is edit??
textField2 = (EditText) findViewById(R.id.textView2);
textField3 = (EditText) findViewById(R.id.textView3);
textField4 = (EditText) findViewById(R.id.textView4);

Answer 2

在您的Java代码中，您的ID不正确：

    textField1 = (EditText) findViewById(R.id.editText2);
    textField2 = (EditText) findViewById(R.id.editText3);
    textField3 = (EditText) findViewById(R.id.editText4);
    textField4 = (EditText) findViewById(R.id.editText5);

在XML中，它们是：

`android:id="@+id/textView2'

依旧......

此外，在XML中，它们是TextView，在Java中，它们是`EditText'。将Java中的ID更改为：

    textField1 = (EditText) findViewById(R.id.textView1);
    textField2 = (EditText) findViewById(R.id.textView2);
    textField3 = (EditText) findViewById(R.id.textView3);
    textField4 = (EditText) findViewById(R.id.textView4);

然后在Java中将它们全部更改为TextView，或者将它们全部更改为EditText。我假设你想要TextView。

初始化View时，您在

中输入的ID

findViewById(R.id.someId)  // This should be an id in your XML

应对应于您在XML文件中创建的id。由于它们是null，因此当您在此处调用方法时，您会获得NPE：

textField1.setVisibility(View.GONE);

我的Android应用无法启动

2 个答案: