我正在尝试构建一个应用程序并且有一些问题。
Android监视器：
08-31 07:41:59.705 10118-10118/com.example.user.rotateit E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.rotateit/com.example.user.rotateit.HasilActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.user.rotateit.HasilActivity.onCreate(HasilActivity.java:24)
at android.app.Activity.performCreate(Activity.java:5008)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
HasilActivity.Java：
public class HasilActivity extends MainActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_hasil);
int choice = 0;
final Random random = new Random();
choice = random.nextInt(2)+0;
EditText et_black = (EditText) findViewById(R.id.et_black);
EditText et_white = (EditText) findViewById(R.id.et_white);
TextView tv_result = (TextView) findViewById(R.id.tv_result);
String et_blackText = et_black.getText().toString();
String et_whiteText = et_white.getText().toString();
if (choice == 0) {
tv_result.setText(et_blackText);
}
if (choice == 1) {
tv_result.setText(et_whiteText);
}
}
}
XML（activity_hasil）：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.user.rotateit.HasilActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text=""
android:id="@+id/tv_result"/>
</LinearLayout>
MainActivity.Java
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ImageView btn_start = (ImageView) findViewById(R.id.btn_start);
btn_start.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent i = new Intent(MainActivity.this, HasilActivity.class);
startActivity(i);
}
});
}
}
XML（activity_main）：
<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#42079D"
tools:context="com.example.user.rotateit.MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<EditText
android:id="@+id/et_black"
style="@style/EditText1"
android:background="#0B0503"
android:textColor="#FEFCFB"
/>
<EditText
android:id="@+id/et_white"
style="@style/EditText1"
android:background="#FEFCFB"
android:textColor="#0B0503"
/>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@mipmap/ic_start"
android:id="@+id/btn_start"
android:layout_gravity="center"/>
</LinearLayout>
</ScrollView>
的Manifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.user.rotateit">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".HasilActivity"></activity>
</application>
</manifest>
运行程序时，应用程序始终停止工作。 这是整个计划。我很确定问题出现在editText中。
基本上，我希望程序本身能够随机显示用户输入的内容。因此，有两个EditTexts，et_black和et_white。用户将输入editText中的任何文本，而程序将显示et_black或et_white。
刚开始学习android studio。
答案 0 :(得分：0)
您必须使用et_black String对象中的文本创建TextEdit。之后，您可以将此字符串分配给tv_result TextView
String et_blackText = et_black.getText().toString();
if (choice == 0 || choice == 1) {
tv_result.setText(et_blackText);
}
此外，您必须在XML中创建以下对象
EditText et_black = (EditText) findViewById(R.id.et_black);
EditText et_white = (EditText) findViewById(R.id.et_white);
TextView tv_result = (TextView) findViewById(R.id.tv_result);
R.id.et_black，R.id.et_white，R.id.tv_result
答案 1 :(得分：0)
您正在尝试将EditText et_black作为TextView的文本。 我不会说别的，只是......仔细查看你的代码!!
PS发布manifest.xml