【发布时间】：2015-03-19 14:55:02
【问题描述】：
我有 2 个活动使用 putExtra 意图将一个字符串变量从一个转移到另一个。我在发送者活动的 onclick 方法中使用了两个按钮，一个按钮从另一个类的数组中检索一个单词并将其发送到接收活动。另一个按钮从 editText 字段发送字符串。但是，我收到一个错误，任何帮助表示赞赏。
发送类
public class TitleScreen extends Activity implements OnClickListener {
Button onePlayer, twoPlayer, play;
EditText inputWord;
String b;
WordDifficulties wordDiff = new WordDifficulties();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_title_screen);
onePlayer = (Button) findViewById(R.id.OnePlayer);
twoPlayer = (Button) findViewById(R.id.TwoPlayer);
play = (Button) findViewById(R.id.Continue);
inputWord = (EditText) findViewById(R.id.enterWord);
inputWord.setVisibility(View.GONE);
play.setVisibility(View.GONE);
onePlayer.setOnClickListener(this);
twoPlayer.setOnClickListener(this);
play.setOnClickListener(this);
}
@Override
public void onClick(View v) {
if (v.getId() == R.id.OnePlayer) {
Intent myIntent = new Intent(TitleScreen.this, MainActivity.class);
myIntent.putExtra("gameWord", wordDiff.getRandomWord());
startActivity(myIntent);
finish();
} else if (v.getId() == R.id.TwoPlayer) {
onePlayer.setVisibility(View.GONE);
twoPlayer.setVisibility(View.GONE);
inputWord.setVisibility(View.VISIBLE);
play.setVisibility(View.VISIBLE);
} else if (v.getId() == R.id.Continue){
// if no word is inputed then game will not start
if(inputWord.getText().toString().trim().length() == 0){
Toast.makeText(getApplicationContext(), "Enter a word",
Toast.LENGTH_SHORT).show();
} else{
Intent myIntent = new Intent(TitleScreen.this, MainActivity.class);
myIntent.putExtra("gameWord", inputWord.getText().toString());
startActivity(myIntent);
finish();
}
}
}
}
在 onCreate 方法中接收活动
Intent myIntent = getIntent();
secretWord = myIntent.getStringExtra("gameWord");
这里是 logCat
Shutting down VM
FATAL EXCEPTION: main
Process: com.example.hunglikeanandroid, PID: 3431
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.hunglikeanandroid/com.example.hunglikeanandroid.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
atandroid.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
at com.example.hunglikeanandroid.MainActivity.<init>(MainActivity.java:35)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1572)
at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
【问题讨论】：
-
你初始化inputWord了吗
-
.MainActivity.<init>(MainActivity.java:35) -
这种情况只发生在 TwoPlayer 点击？
-
是的，输入词只发生在 TwoPlayer 点击，OnePlayer 点击仍然崩溃
-
检查您的 MainActivity 或发布第 35 行，因为该类正在创建错误。