Question

我在将OnclickListener分配给动态创建的按钮时出现了一些错误

当我调用getText函数时，它会收到最后创建的按钮的值（点击任何按钮）。
我想通过点击那些按钮开始一项新活动，但它提供了java.lang.nullpointerexception。

这是我的代码：

public void getTableList(LinearLayout layout, String s) {
    Log.e("in getTableList", "in getTableList");
    b = new Button(shuddhContext);
    b.setText(s);
    b.setTextSize(15);
    LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
            LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
    params.setMargins(5, 5, 5, 5);
    b.setBackgroundResource(R.drawable.class_button);
    b.setLayoutParams(params);
    b.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent myIntent = new Intent(
                "com.shuddhatm.attendencemonitor.STUDENTLIST");
            String className = b.getText().toString();

            myIntent.putExtra("className", className);
            try{
                startActivity(myIntent);
            }catch(Exception e){
                Toast.makeText(shuddhContext, e.toString() + "\n" + b.getText(), Toast.LENGTH_LONG).show();
            }
        }
    });
    layout.addView(b);
}

with try / catch block

04-13 23:32:38.561: D/memalloc(7243): ion: Unmapping buffer  base:0x5305a000 size:245760
04-13 23:32:38.561: D/memalloc(7243): ion: Unmapping buffer  base:0x50281000 size:4096
04-13 23:32:41.331: E/button Click(7243): step1
04-13 23:32:41.331: E/button Click(7243): step2
04-13 23:32:41.331: E/button Click(7243): step3
04-13 23:32:41.331: E/button Click(7243): step4
04-13 23:32:41.381: D/memalloc(7243): ion: Mapped buffer base:0x5305a000 size:245760 offset:0 fd:74
04-13 23:32:41.391: D/memalloc(7243): ion: Mapped buffer base:0x50281000 size:4096 offset:0 fd:76
04-13 23:32:42.931: E/button Click(7243): step1
04-13 23:32:42.931: E/button Click(7243): step2
04-13 23:32:42.931: E/button Click(7243): step3
04-13 23:32:42.931: E/button Click(7243): step4
04-13 23:32:44.881: D/memalloc(7243): ion: Unmapping buffer  base:0x5305a000 size:245760
04-13 23:32:44.881: D/memalloc(7243): ion: Unmapping buffer  base:0x50281000 size:4096
04-13 23:32:44.931: D/memalloc(7243): ion: Mapped buffer base:0x5305a000 size:245760 offset:0 fd:74
04-13 23:32:44.931: D/memalloc(7243): ion: Mapped buffer base:0x50281000 size:4096 offset:0 fd:76
04-13 23:32:48.371: D/memalloc(7243): ion: Unmapping buffer  base:0x5305a000 size:245760
04-13 23:32:48.371: D/memalloc(7243): ion: Unmapping buffer  base:0x50281000 size:4096

logcat（不带try / catch块）：

04-13 23:48:50.901: D/memalloc(8869): ion: Mapped buffer base:0x53ef4000 size:1536000 offset:0 fd:65
04-13 23:48:50.901: D/memalloc(8869): ion: Mapped buffer base:0x4006f000 size:4096 offset:0 fd:68
04-13 23:48:50.981: E/button Click(8869): step1
04-13 23:48:50.981: E/button Click(8869): step2
04-13 23:48:50.981: E/button Click(8869): step3
04-13 23:48:50.981: E/button Click(8869): step4
04-13 23:48:50.981: W/dalvikvm(8869): threadid=1: thread exiting with uncaught exception (group=0x41275540)
04-13 23:48:51.041: E/AndroidRuntime(8869): FATAL EXCEPTION: main
04-13 23:48:51.041: E/AndroidRuntime(8869): java.lang.NullPointerException
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.app.Activity.startActivityForResult(Activity.java:3409)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.app.Activity.startActivityForResult(Activity.java:3370)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.app.Activity.startActivity(Activity.java:3580)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.app.Activity.startActivity(Activity.java:3548)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at com.shuddhatm.attendancemonitor.AMData$1.onClick(AMData.java:142)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.view.View.performClick(View.java:4102)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.view.View$PerformClick.run(View.java:17085)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.os.Handler.handleCallback(Handler.java:615)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.os.Looper.loop(Looper.java:155)<br />
04-13 23:48:51.041: E/AndroidRuntime(8869):     at android.app.ActivityThread.main(ActivityThread.java:5520)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at java.lang.reflect.Method.invokeNative(Native Method)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at java.lang.reflect.Method.invoke(Method.java:511)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:796)
04-13 23:48:51.041: E/AndroidRuntime(8869):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

我认为这里的主要问题是尝试获取Button点击的文字，而b方法中的onClick变量无法访问它如果它不是final。为避免这种情况，您可以按如下方式检索单击的视图（因为此处为b == v）：

@Override
public void onClick(View v) {
    // b == v
    String className = v.getText().toString();
}

另一个问题可能是您的Intent声明：

Intent myIntent = new Intent("com.shuddhatm.attendencemonitor.STUDENTLIST");

我猜“ com.shuddhatm ... STUDENTLIST ”是新Activity，我建议您按照以下步骤操作：

Intent intent = new Intent(AMData.this, STUDENTLIST.class);

According to the documentation：

这里使用的构造函数有两个参数：
   - Context 作为其第一个参数（因为Activity类是Context的子类，所以使用它）
   - 系统应向其传递Intent的应用程序组件的类（在这种情况下，应该启动的活动）

然后，因为AMData和STUDENTLIST在同一个包中，您可以避免写出该类的全名。
最后，确保shuddhContext返回正确的上下文。如果没有，您应该使用AMData.this。你可以避免使用try/catch Intent方法，我认为这是没用的。

希望这有帮助。

创建从数据库中获取价值并分配onclick监听器的按钮

1 个答案: