Android：單擊時按鈕不顯示模擬器中的輸出文本

Question

更新：我已將活動代碼更改為我的最佳工作集。 我當前的問題是，單擊按鈕時，App強制在模擬器中關閉。 我的Logcat說，問題出在第38行，在switch語句中調用updateDate（），在第64行，設置當前日期的文本。

我創建了一個具有兩個按鈕的應用程序，當您在Android模擬器中打開並單擊時，它們會向您顯示當前日期和時間，按鈕下方沒有顯示應有的文本。 我正在按鈕下方使用TextView來顯示輸出。 這分別是我的main.xml和activity中的代碼。

main.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="top"
    android:orientation="vertical" >

    <Button
        android:id="@+id/dayOf"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/buttonDay"
        />

    <Button
        android:id="@+id/clock"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/buttonTime" 
        />

    <TextView
        android:id="@+id/info"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/output"
        android:textSize="72dip"
        />

</LinearLayout>

活動

package omaxwell.CS211D.TimeAndDate;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import java.util.Calendar;
import android.widget.TextView;
/*
 * This is the activity for my Android App that gives you the date and time 
 */
//*******************TimeAndDateActivity*******************
public class TimeAndDateActivity extends Activity implements View.OnClickListener
{
    Button dayOf;
    Button clock;
    @Override
    //*******************onCreate*******************
    public void onCreate(Bundle b)
    {
        super.onCreate(b);
        setContentView(R.layout.main);

        clock = (Button)this.findViewById(R.id.clock);   //Time Button
        clock.setOnClickListener(this);

        dayOf = (Button)this.findViewById(R.id.dayOf);   //Date Button
        dayOf.setOnClickListener(this);
    }
        //*******************onClick*******************
        public void onClick(View v) //Called when one of the buttons above is clicked
        {
            switch(v.getId())
            {
                case R.id.clock:
                    updateTime();
                    break;
                case R.id.dayOf:
                    updateDate();
                    break;
            }

        }
            //*******************updateTime*******************
            private void updateTime()
            {
                Calendar d = Calendar.getInstance();
                d.getTime();

                TextView tv = (TextView) findViewById(R.string.output);
                tv.setText(d.getTime().toString());
            }
            //*******************updateDay*******************
            private void updateDate()
            {
                Calendar c = Calendar.getInstance();

                int day = c.get(Calendar.DAY_OF_MONTH);
                int month = c.get(Calendar.MONTH);
                int year = c.get(Calendar.YEAR);

                String date = String.valueOf(day) + "-" + String.valueOf(month) + "-" +String.valueOf(year);

                TextView tv = (TextView) findViewById(R.string.output);
                tv.setText(date);
            }


}

提前致謝 ：）

Answer 1

創建textView之后，您也添加了它。

TextView tv = new TextView(this);
                tv.setText(date);

獲取內容查看並說，

contentLayout.addView(tv);

Answer 2

看起來您在updateDate（）中創建了一個新的Textview，但是您並未對其進行任何操作。 相反，只需更新您現有的Textview：

TextView txt = (TextView) findViewById(R.id.info);
txt.setText(date);

Answer 3

我認為您沒有將OnClickListener設置為button

public void onCreate(Bundle b)
        {
           super.onCreate(b);
           setContentView(R.layout.main);
           clock = (Button)this.findViewById(R.id.clock);   //Time Button
           dayOf = (Button)this.findViewById(R.id.dayOf);   //Date Button
           clock.setOnClickListener(this);
           dayOf.setOnClickListener(this);

        }

Answer 4

這應該工作：

package omaxwell.CS211D.TimeAndDate;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import java.util.Calendar;
import android.widget.TextView;
/*
 * This is the activity for my Android App that gives you the date and time 
 */
//*******************TimeAndDateActivity*******************
public class TimeAndDateActivity extends Activity implements View.OnClickListener
{
    Button dayOf;
    Button clock;
    TextView info;

    @Override
    //*******************onCreate*******************
    public void onCreate(Bundle b)
    {
        super.onCreate(b);

        this.setContentView(R.layout.main); // set content view firstly


        clock = (Button)this.findViewById(R.id.clock);   //Time Button
        dayOf = (Button)this.findViewById(R.id.dayOf);   //Date Button
        // set OnClickListener, you can also use the "android:click" attribute in the XML
        clock.setOnClickListener(this);
        dayOf.setOnClickListener(this);

        info = (TextView)this.findViewById(R.id.info);   //TextView
    }

        //*******************onClick*******************
        public void onClick(View v) //Called when one of the buttons above is clicked
        {
            switch(v.getId())
            {
                case R.id.clock:
                    updateTime();
                    break;  // don't forget break ! Otherwise, updateDate() will be execute

                case R.id.dayOf:
                    updateDate();
                    break;
            }

        }

            //*******************updateTime*******************
            private void updateTime()
            {
                Calendar d = Calendar.getInstance();
                d.getTime();

                // just update info
                info.setText(d.getTime().toString());

                // Following is wrong!
                //TextView tv = new TextView(this);
                //tv.setText(d.getTime().toString());
                //  setContentView(R.id.info);
            }

            //*******************updateDay*******************
            private void updateDate()
            {
                Calendar c = Calendar.getInstance();

                int day = c.get(Calendar.DAY_OF_MONTH);
                int month = c.get(Calendar.MONTH);
                int year = c.get(Calendar.YEAR);

                String date = String.valueOf(day) + "-" + String.valueOf(month) + "-" +String.valueOf(year);

                // just update info
                info.setText(d.getTime().toString());

                // Following is wrong!
                //TextView tv = new TextView(this);
                //tv.setText(date);
                // setContentView(R.id.info);
            }
}