java.lang.ClassCastException for interface On android java

Question

我在下面有一个 Dialog 片段类，它的接口抛出以下异常：

**java.lang.ClassCastException: **

public class FolderPickerDialog extends DialogFragment {
    @Override
    public void onAttach(Context context) {
        this.listner=(FolderPickerDialog.FolderPickerListner)context;
        super.onAttach(context);
    }

    public interface FolderPickerListner {
        void onFolderSelected(String path)
    }
}

我已经在下面的类中实现了监听器：

public class SaveDialog extends DialogFragment implements FolderPickerDialog.FolderPickerListner {

    @Override
    public void onFolderSelected(String path) {
        ic_path.setText(path);
    }

}

我的原木猫

java.lang.ClassCastException: com.nanosoft.icstudio.activities.MainActivity cannot be cast to com.nanosoft.icstudio.Dialogs.FolderPickerDialog$FolderPickerListner
at com.nanosoft.icstudio.Dialogs.FolderPickerDialog.onAttach(FolderPickerDialog.java:43)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1231)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1528)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1595)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:758)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2363)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2149)
at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2103)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2013)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:710)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:207)
at android.app.ActivityThread.main(ActivityThread.java:5765)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:107)

Answer 1

错误说明的是这一行：

this.listner=(FolderPickerDialog.FolderPickerListner) context;

您尝试将context（即MainActivity 的上下文）转换为FolderPickerDialog.FolderPickerListner 对象，这是不可能的。

Answer 2

要通过生命周期事件将侦听器回调传递给FolderPickerDialog，您可以执行以下操作：

在FolderPickerDialog:

private FolderPickerListner listener;
...
@Override
    public void onAttach(Context context) {
        this.listener=(FolderPickerListner)context;
        super.onAttach(context);
    }

活动中：

public class MainActivity extends AppCompatActivity implements FolderPickerDialog.FolderPickerListner {

...


}