使用EditText设置按钮文本

Question

下面是更新后的版本: Main xml：

<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: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="com.example.names.MainActivity$PlaceholderFragment" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="23dp"
        android:onClick="nextScreen"
        android:text="@string/Next" />

    <EditText
        android:id="@+id/editText2"
        android:hint="Player B"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editText1"
        android:layout_marginTop="31dp"
        android:ems="10" />

    <EditText
        android:id="@+id/editText1"
        android:hint="Player A"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/editText2"
        android:layout_below="@+id/button1"
        android:layout_marginTop="46dp"
        android:ems="10" />

</RelativeLayout>

Next-按钮在main中调用方法nextScreen：

public void nextScreen (View view)
{
    EditText ed1 = (EditText)findViewById(R.id.editText1);
    EditText ed2 = (EditText)findViewById(R.id.editText2);

    Intent intent = new Intent (this, ButtonsActivity.class);
    intent.putExtra("string_A", ed1.getText());
    intent.putExtra("string_B", ed2.getText());
    startActivity(intent);
}

和第二个练习中的onCreate：

protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_buttons);

    Button btn1 = (Button)findViewById(R.id.player_A);
    Button btn2 = (Button)findViewById(R.id.player_B);

    btn1.setText((CharSequence) getIntent().getExtras().get("string_A"));
    btn2.setText((CharSequence) getIntent().getExtras().get("string_B"));

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment()).commit();
    }
}

当我在EditTexts中输入一些文本时，我按下next按钮，应用程序崩溃。Logcat-

05-04 15:21:54.922: E/AndroidRuntime(2025): FATAL EXCEPTION: main
05-04 15:21:54.922: E/AndroidRuntime(2025): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.names/com.example.names.ButtonsActivity}: java.lang.NullPointerException
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2092)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2117)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.app.ActivityThread.access$700(ActivityThread.java:134)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1218)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.os.Looper.loop(Looper.java:137)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.app.ActivityThread.main(ActivityThread.java:4867)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at java.lang.reflect.Method.invokeNative(Native Method)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at java.lang.reflect.Method.invoke(Method.java:511)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1007)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:774)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at dalvik.system.NativeStart.main(Native Method)
05-04 15:21:54.922: E/AndroidRuntime(2025): Caused by: java.lang.NullPointerException
05-04 15:21:54.922: E/AndroidRuntime(2025):     at com.example.names.ButtonsActivity.onCreate(ButtonsActivity.java:24)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.app.Activity.performCreate(Activity.java:5047)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
05-04 15:21:54.922: E/AndroidRuntime(2025):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2056)
05-04 15:21:54.922: E/AndroidRuntime(2025):     ... 11 more

Answer 1

您不能从未设置为上下文视图的布局文件中按id获取视图。在调用第二个活动时，您应该将想要在按钮上显示的字符串设置为Intent的附加字符串

Intent intent = new Intent(this, SecondActivity.class);
intent.putExtra("Str1", ed1.getText().toString());
intent.putExtra("Str2", ed2.getText().toString());
startActivity(intent);

在你的第二个练习中：

btn1.setText(getIntent().getExtras().get("Str1"));
btn2.setTextgetIntent().getExtras().get("Str2"));

这是在活动之间共享数据的最佳方式。

Answer 2

像这样做

Intent intent = new Intent(this, SecondActivity.class);
intent.putExtra("string_A", ed1.getText().toString()); //see .toString();
intent.putExtra("string_B", ed2.getText().toString());

得到这样的结果。

getIntent().getStringExtra("string_A");